Acids,Bases and Salts

BASIC CONCEPTS:

We are familiar with the utility and important of acids, bases and salts in

our daily life. For example

The sour taste of vinegar is due to acetic acid (CH3COOH).

Sodium hydroxide (NaOH) is a base, which is used in the

preparation of soaps.

Sodium Chloride (NaCl) is common salt, which is useful as food

ingredient.

It may not be possible to identify all the salts by their taste as in case of

acids and bases. They have their own characteristics which help in their

identification. Apart from common salt (NaCl0, washing soda, baking

soda, copper sulphate etc. are some of the well known salts we came

across quite often. In general, salts, are formed by the chemical

combination of acids and bases.

In this chapter, we will discuss all the three types of compounds : acids,

bases and salts. In order to know whether a substance is an acid or a base

we should first know the meaning of the term acid-base indicator or just

indicator.

1. Indicators: It is ‘dye’ that changes color when it is put into acid or

a base. It gives different colors in acid and base. The three

2. common indicators to test for acids and bases are : Litmus, Methyl

orange and phenophthalein.

The most common indicator used testing acids and bases

in the laboratory is litmus, which can be used in the form

of litmus solution or in the form of litmus paper. It is of

two types : blue litmus and red litmus. Litmus is a natural

indicator, whose neutral colour is purple.

IMPORTANT FACTS:

1. An acid turns blue litmus to red.

2. A base (or alkali) turns red litmus to blue.

The methyl orange is a synthetic indicator whose neutral colour is orange.

(i) Methyl orange indicator gives pink colour in acid solution.

(ii) Methyl orange indicator gives yellow in basic solution.

The phenolphthalein is a synthetic whose neutral colour is

‘colourless’.

IMPORTANT FACTS:

(i) Phenolphthalein indicator is colourless in acid solution.

(ii) Phenolphthalein indicator gives pink colour in basic solution.

Olfactory indicators: The ‘olfactory’ means relating to

the sense of smell. Those substances whose smell changes

in acetic or basic solutions are called olfactory indicators.

IMPORTANT FACTS:

Onion has characteristics smell. When a basic solution like sodium

hydroxide solution is added to a cloth stripe treated with onions, then

onion smell cannot be detected. An acetic solution like hydrochloric acid,

however, does not destroy smell of onions. Thus can be used as a test for

acids and bases.

2. General Characteristics Properties of Acids:

Sour Taste: Almost all acidic substances have a sour taste.

Action on Litmus Paper: Acids turns blue litmus to red.

Action on Methyl Orange: Methyl orange turns pink

when its solutions are added the solution of an acidic

substances.

Corrosive Nature: Most of the acids are corrosive in

nature. They produce a burning sensation on the skin and

holes in the clothes on which they fall.

Reaction with Metals: Acids react with active metals like zinc,

magnesium etc. generally with the evolution of hydrogen gas. The

reactions may be represented as follows:

Zn(s) + dil. H2SO4(aq) ZnSO4(aq) + H2(g)

Zn(s) + 2HCl(aq) ZnCl2(aq) + 2HCl(aq)

It is a displacement reaction. In this reaction hydrogen of H2SO4 is

displayed by zinc. This proves that sulphuric acid contains

replacable hydrogen.

Tips for students:

The metal in the above reactions displaces hydrogen from the acids. This is seen as

hydrogen gas. The metal combines with remaining part of the acids and forms a

compound called a salt.

The reaction of a metal with an acid can be summarized as:

Acid + Metal Salt + Hydrogen gas

Reaction with Metal Carbonates:

Acids decomposes metal carbonates to liberate carbon dioxide and to form

corresponding salts and water.

Metal carbonate + Acid Salt + Water + Carbon dioxide

(i) When sodium carbonate is treated with dilute hydrochloric acid the carbon

dioxide is liberated and sodium chloride and water are formed.

Na2CO3(s) + 2HCl(aq) 2NaCl(aq) + H2O + CO2(g)

(ii) When calcium carbonate is treated with dilute hydrochloric acid then carbon

dioxide is liberated and calcium chlorine and water are formed.

CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + CO2(g)

Reaction with Metal Hydrogen Carbonates:

Acids react with metal bicarbonates to give out carbon dioxide with

effervescence and forming the corresponding salt and water.

NaHCO3(aq) + HCl(aq) NaCl(aq) + H2O(l) + CO2(g)

Reaction with Bases: When an acid reacts with a base, it forms

salt and water. As a result the acidic properties of the acid

disappear. The process is called neutralization.

Or

The reaction between an acid and a base to give a salt and water is known as

a neutralization reaction.

Example : NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)

Reaction with Metallic Oxides: Metallic oxides like quick time i.e.,

calcium oxide (CaO), Copper (II) oxide (CuO), magnesium oxide (MgO)

etc. react with acids to form salt and water.

CaO(s) + 2HCl(aq) CaCl2(aq) + H2O

(salt) (water)

CuO(s) + 2HCl(aq) CuCl2(aq) + H2O

(salt) (water)

3. General Characteristics Properties of Bases:

Bases have Bitter Taste: Bases possess a bitter taste.

Slipper or Soapy Touch: They possess a slippery touch like soaps.

Action on Litmus Paper: They turn red litmus blue.

Action on Phenolphthalein: They turn phenolphthalein solution pink.

Corrosive Nature : Some bases like caustic soda (sodium hydroxide),

caustic potash (potassium hydroxise) etc. produce a burning sensation on

the skin.

Reaction with Bases: The reaction between an acid and a base is called

neutralization reaction. This reaction gives a salt and water.

NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)

Reaction with Metals: Some bases like sodium hydroxide and potassium

hydroxide react with active metals like zinc and aluminium to liberate

hydrogen gas with formation of salt.

2 NaOH + Zn Na2ZnO2 + H2

(sodium hydroxide) (zinc) (sodium zincate) (hydrogen)

2 NaOH + 2 Al + H2O 2NaAlO2 + 3H2

(sodium hydroxide) (aluminium) (water) (sodium aluminate)

Reaction with Non Metallic Oxides: When carbon dioxide (CO2) which is

a non metallic oxide passed through lime water that is Ca(OH)2 which is a

base, they react to produce salt (CaCO3) and water.

Ca(OH)2(aq) + CO2(g) CaCO3(s) + H2O(l)

(lime water) (white precipitate)

KNOWLEDGE BOOSTER

All bases react with acids to form salt and water, this shows that non-metallic oxides

are acidic in nature.

4. What Happens to a Base in a Water Solution?

When bases are dissolved in water, they produce hydroxide ions in the

solution. For example,

NaOH + Water Na+ + OH-

NH4OH + Water NH4+ + OH-

KOH + Water K+ + OH-

Mg(OH)2 + Water Mg2+ + 2OH-

Thus, a base is defined as follows:

A base is a substance which when dissolved in water gives (OH-) ions in the

solution.

KNOWLEDGE BOOSTER

(i) The compound C2H5OH contains –OH group but it does not ionize in the

aqueous solution to gives OH-ions. Hence,it is not a base.

(ii) All bases do not dissolve in water. An alkali is a base that dissolves in

water. They are soapy to touch,bitter and corrosive as they may cause

harm.

(iii) Never taste or touch them as they may cause harm.

5. What Happens to an Acid or a Base in a Water Solution?

When acids are dissolved in water.They give free hydronium ions (H3O+ or H+)

Examples:

HCl(g)+H2O(l) H3O+(aq)+Cl-(aq)

H2so-(aq)+ H2O(l) 2 H3O

+(aq)+SO42-(aq)

CH3COOH(aq) +H2O(l) H3O+(aq)+ CH3COO-(aq)

Thus, an acid is defined as follows:

An acid is a substance which when dissolved in water, gives hydronium ions (H3O+ or

H+) in the solution.

6. Mixing of Bases or Acids with Water –An Exothermic Process:

The process of mixing bases or acids in water is a highly exothermic reaction. If

we dissolve bases like sodium hydroxide or potassium hydroxide in water, the

solution is found to be hotter. This shows that dissolution of bases in water is an

exothermic process.

KNOWLEDGE BOOSTER

The acid must always be added slowly to water with constant stirring. If

water is added to a concentrated acid, the heat generated may cause the

mixture to splash out and cause burns.

7. Effect of Dilution on Hydroxide (OH-)Ions and Hydronium(H+) ions and

Concentration of Acids and Bases: Mixing an acid or base with water

results in decrease in the concentration of ions( H3O+/ OH-)per volume such a

process is called dilution and the acid or the base is said to be diluted.

8. Strong and Weak Acids:The acids which are almost completely ionized

when dissolved in water are called strong acids.

Hydrochloric acids(HCl),Nitric acids(HNO3) and sulphuric acids (H2SO4)are

strong acids because they give large around of H+ ions in the solution. Such

acids are called strong acids. Their dissociation is represented by putting a

single arrow () towards the ions produced showing their complete

dissociation or ionization.

HCl + water H+(aq) + Cl-(aq)

HNO3 + Water H+(aq) + NO3-(aq)

H2SO4 + Water 2H+(aq) + SO42-(aq)

On the other hand, acids like acetic acid (CH3COOH), formic acid (HCOOH).

Carbonic acid (H2CO3).Phosphoric acid (H3PO4) etc. when dissolved in water

dissociate only partially in the solution. As a result the amount of H+ ions

produced in small. Such acids are called weak acids.

Thus, the acids which are partially ionized when dissolved in water are called

weak acids.

CH3COOH + Water CH3COO-(aq) + H+(aq)

acetic ion

H2CO3 + Water 2H+(aq) + CO32-(aq)

Hydrogen ion

HCOOH + Water HCOO-(aq) + H+(aq)

Formate ion

9. Strong and weak bases: Bases which are almost completely dissociated

ionized in their solution are called strong bases.

Bases like sodium hydroxide (NaOH) and potassium hydroxide (KOH) when

dissolved in water dissociate completely into ions. As a result, they give large

amount of OH- ions. Their dissociation is represented by putting a single

arrow () towards the ions produced. Thus

NaOH + Water Na+(aq) + OH-(aq)

KOH + Water K+(aq) + OH-(aq)

On the other hand, bases like ammonium hydroxide (NH4OH). Calcium

hydroxide, Ca(OH)2 etc. when dissolved in water dissociate only partially to

give hydroxide ions. As a result the amount of OH- ions produced in the

solution is small.

Thus, the bases which are partially dissociated/ionized in their aqueous

solution are called weak bases.

10. How Strong Are Acid or Base Solution: The strength of any solution of an

acid or base can be determined from the concentration of H+(aq) or OH-(aq) in

the solution.

We can do this by making use of universal indicator, which is a mixture of

several indicators. The universal indicators show different colours of mixtures

at different concentrations of hydrogen ions in a solution.

A Danish Biochemist S.P.Sorensen (1909) proposed that strength of acidity of

a solution be expressed in terms of parameter called pH. The p in pH stands

for ’poting’ in Germans meaning power. On the pH scale we can measure pH

from O (very acidic) to 14 (very alkaline). Higher the hydronium ion

concentration, lower is pH value. The pH of a neutral solution is 7 to 14, it

represents an increase in OH- ion concentration in the solution, that increase in

the strength of alkali.

KNOWLEDGE BOOSTER:

[H+] = [OH-], then the solution to be neutral.

[H+] > [OH-], then the solution is said to be acidic.

[H+] < [OH-], then the solution is said to be alkaline or basic.

Relationship between pH values and the acidic or basic nature of any aqueous

solution at 298K is shown below:

Fig.2.1. The pH values and the acidic or basic nature of any aqueous solution at 298K

(-250C).

The pH values of some common solutions are given below:

pH values of some common solution:

Solution pH

Blood

Saliva

Urine

Gastric juice

Coffee

Beer

Tomato juice

Wine

Lemon juice

Vinegar

HCl (1M)

7.36 – 7.42

6.5 – 7.5

6.7 – 7.5

1.0 – 2.0

4.5 – 5.5

4.0 – 5.0

4.0 – 44

2.8 – 3.8

2.2 – 24

2.5 – 3.5

0

NaOH (1M)

NH4OH (1M)

Mg(OH)2 (saturated)

Battery acid (40% H2SO4)

14

11.6

10.5

0.5

11. Importance of pH in Everyday Life:

In biological Systems (i.e., Plants and Animals): Our body works within

the range of 7.0 to 7.8. The pH plays an important role in the survival of

animals, including human beings. Living organisms can survive only in

narrow range of pH change.

When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into

the rivers, it lowers the pH of the river water. The survival of aquatic life in such

rivers becomes difficult.

Most of the plants grow best pH of the soil is close to 7. If the soil is too acidic or too

basic, the plants grow badly or do not grow at all. The soil may be acidic or basic

naturally. The soil pH is also affected by the use of chemical fertilizers in the field.

The pH of acidic soil can reach as low as 4 and that of the basic soil can go upto 8.3.

Chemicals can be added to soil to adjust its pH and make if suitable for growing

plants.

In Digestive System: pH a vital role in the digestion of food and other

biochemical reaction inside the human/animal body. Our stomach produces

hydrochloric acid which helps in the digestion of food without harming the

stomach. During indigestion the stomach produces two much acid and this

cause pain and irritation. The problem is called ‘acidity’. It is cured by

medicines called ‘Antacid’. The most common used antacid contains

magnesium hydroxide which is a weak base and neutralizes the excess

acid.

Tooth Decay Caused by Acids: Tooth decay starts when the pH of the

mouth is lower than 5.5. Tooth enamel made up of calcium phosphate is

the hardest substance in the body. It does not dissolve in water but is

corroded when the pH in the mouth is below 5.5. Bacteria present in the

mouth produce acids by degradation of sugar and food particles remaining

in the mouth after eating. The amount of acid produced is high when we

eat sweets or sugary food. The saliva produced in the mouth by the

salivary glands is alkaline and partially neutralizes the acids produced in

the mouth. However, the excess acid has to be removed by cleaning the

teeth with a good quality tooth paste. These tooth pastes are alkaline in

nature and neutralize the excess acid present in the mouth and prevent

tooth decay.

Self Defence Animals and Plants through Chemicals Warfare: When we

are stung by an honey bee or yellow ant we feel pain or irritation. This is

due to the acid (formic acid i.e.methanoic acid), injected into our skin by

the bee or the ant. To get the relief, we apply the solution of mild base like

baking soda. Similarly, nettle plants have leaves with stinging hairs. If

these are touched accidently they cause a lot of pain again due to formic

acid injected by these leaves into the skin.

Nettle is a herbaceous plant which grows in the wild. Its leaves have stinging hair,

which cause painful stings when touched accidently. This is due to the methanoic acid

secreted by them. A traditional remedy is rubbing the area with the leaf of the duck

plant, which often grows beside the nettle in the wild.

Given below is the table of some naturally occurring acids:

Natural Source Acid Natural Source Acid

Vinegar

Orange

Tamarind

Tomato

Acetic acid

Citric acid

Tartaric acid

Oxalic acid

Sour milk (curd)

Lemon

Anti sting

Nettle sting

Lactic acid

Citric acid

Methanoic acid

Methanoic acid

12. Salts: Salts are the ionic compounds consisting of two parts, one part

carrying a positive charge and the other carrying a negative charge. Salt as a

whole is electrically neutral because the number of positive and negative ions

present in the salt are equal.

Or

Salt is a product of neutralization reaction between an acid and a base.

Example:

NaOH + HCl NaCl + H2O

(base) (acid) (salt) (water)

NH4OH + HCl NH4Cl + H2O

(base) (acid) (salt) (water)

KOH + HNO3 KNO3 + H2O

(base) (acid) (salt) (water)

MgO + H2SO4 MgSO4 + H2O

(base) (acid) (salt) (water)

Some common salts and their formulae:

Table 2.1: Some Common Salts and Their Formulae

Salt Formulae Positive ion Negative ion

Sodium chloride

Sodium sulphate

Sodium nitrate

Potassium nitrate

Copper sulphate

Zinc sulphate

Calcium carbonate

Sodium carbonate

Calcium chloride

Aliminium sulphate

Ammonium chloride

NaCl

Na2SO4

NaNO3

KNO3

CuSO4

ZnSO4

CuCO3

Na2CO3

CaCl2

Al2(SO4)3

NH4Cl

Na+

2Na+

Na+

K+

Cu2+

Zn2+

Ca2+

2Na+

Ca2+

2Al3+

NH4+

Cl

SO42-

NO3-

NO3-

So42-

So42-

CO32-

CO32-

2Cl-

3SO42-

Cl-

Family of Salts: The salts are classified into different families either on the basis of

the acid or on the basis of the base from which they have been obtained.

The parent acids and bases of some salts are identifies as follows:

Table 2.2: Writing the Names of Some Salts:

Formula of the Salt Parent Name of the Salt

Acid Base

1. Na2CO3

2. CaCO3

3. CaSO4

4. Ca3(PO)4)2

5. CuSO4

6. CH3COONa

H2CO3

Carbonic

acid

H2CO3

Carbonic

acid

H2SO4

Sulphuric

acid

H3PO4

Phosphoric

acid

H2SO4

Sulphuric

acid

CH3COOH

Acetic acid

NaOH

Sodium

hydroxide

Ca(OH)2

Calcium

hydroxide

Ca(OH)2

Calcium

hydroxide

Ca(OH)2

Calcium

hydroxide

Cu(OH)2

Copper

hydroxide

NaOH

Sodium

hydroxide

Sodium carbonate

Calcium carbonate

Calcium sulphate

Calcium phosphate

Copper sulphate

Sodium acetate

pH of Salts : A salt is formed by the reaction between an acid and a base, so we

should expect that the solution of a salt in water will be neutral towards litmus.

Though the aqueous solutions of many salts are neutral (having pH of 7). Some salts

produce acidic or basic solution when dissolved in water. The pH values of some of

the salt solutions are given below:

Salt Solution pH Nature

Sodium chloride solution

Ammonium chloride solution

Sodium carbonate solution

7

6

9

Neutral

Acidic

Basic

Depending upon the nature of the acid and base reacting to form the salt,the salts can

be classified in to the following four types:

1. Salts of strong acid an strong base : A few examples are given

below:NaCl,NaNO3,KCl,K2SO4,KNO3. These salts on dissolving in water

produce strong acid and strong base.

Example:

NaCl + H2O NaOH + HCl

Strong base Strong acid

Hence, the acid and the base produce neutralize each other completely. As a result the

solution is neutral with pH=7.

2. Salts of weak acid and strong base: A few examples are given below:

Na2CO3, NaHCO3, CH3COONa

These salts on dissolving in water produce a strong base and weak acid,

Example:

Na2CO3 + 2H2O 2NaOH + H2CO3

Strong base Weak Acid

The strong base produced dominates over the weak acid. Hence,the solution is basic

with pH>7.

3. Salts of strong acid and weak base: A few examples are given below:

NH4Cl ,CuSO4,AlCl3,ZnSO4 etc.

These salts on dissolving in water produce a strong acid and weak base.

example:

CuSO4 + 2H2O Cu(OH)2 + H2SO4

Copper(II)Sulphate Copper(II)hydroxide Sulphuric acid

(weak base) (Strong acid)

The strong base produces dominates over the weak base. Hence, the solution is acidic

with pH<7.

4. Salts of weak acid and weak base.

Example: CH3COONH4

(Ammonium Aceatate)

When this salt is dissolved in water, it produces weak acid and weak base. Hence, the

solution is almost neutral.

13. Chemical from Common Salt: Chemically common salt is sodium

chloride.Its simples formula is NaCl. This is the Salt that you use in food.

The main source of common salt is the sea water. Sea water contains about 3.5%

of soluble salts, the most common of which is sodium chloride (2.7 to 2.9%)

Common salt is also found in the form of solid deposits in several ports of the world.

Due to the presence of impurities, it is often brown in color and is called rock salt.

Beds of rock salt were formed, when seas/lakes dried up the past.

Common Salt – A Raw Material for Chemicals: We can obtain many useful

substances/chemicals from common salt. Thus, the common salt is the raw material

for many chemicals.

These chemicals are:

Sodium hydroxide(NaOH)

Bleaching powder (CaOCl2)

Sodium hydrogen carbonate (NaHCO3)

Sodium Carbonate(Na2CO3)

14. Sodium Hydroxide: NaOH commercially, sodium hydroxide is also called

caustic soda. It is a strong base.

Manufacture of Sodium Hydroxide by Common Salt : Sodium hydroxide is

manufactured by electrolysis of an aqueous solution of sodium chloride(called

brine).This process is called chloralkali process because of the products formed chlor

for chlorine and alkali for sodium hydroxide.When electricity is passed through

brine(aqueous solution of sodium chloride),the following reactions take place.

2NaCl(aq)+2H2O(l) 2NaOH(aq)+Cl2(g)+H2(g)

During the electrolysis, chlorine gas is produced at the anode (positive electrode)and

hydrogen gas is produced at the cathode(negative electrode) sodium hydroxide

solution is formed near the cathode.

i.e. At cathode: H+ + e- H

H + H H2

At anode: Cl- Cl + e-

Cl + Cl Cl2

Uses: The three useful products obtained by the electrolysis of an aqueous solution of

sodium chloride are: (1) Hydrogen ,(2) Chlorine and (3) Sodium hydroxide.

1. Uses sodium hydroxide:

For degreasing sheets/rods etc.

For manufacturing soaps and detergents.

For manufacturing paper.

For making artificial textile fibres.

2. Uses of Chlorine : It is used :

As germicide and disinfectant for sterilization of water in the

swimming pool.

In the manufacture of bleaching powder,chloroform,hydrochloric acid,

explosives like DDT etc.

In the manufacturing of hydrochloric acid.

In the manufacturing of poly vinyl chloride (PVC), pesticides,

chlorofluoro carbons (CFC’s), chloroform. Carbon tetrachloride,

paints dye-stuffs.

3. Uses of Hydrogen : It is used :

In the hydrogenation of oils to obtain solid fats.

In the production of hydrochloric acid.

To make ammonia for fertilizers.

To make methanol

15. Bleaching Powder: Chemically it is a calcium oxychloride, CaOCl2 or

Ca(OCl)Cl. It is also called chloride of lime.

Preparation: Bleaching powder is produced by the action of chlorine on dry

slaked lime [Ca(OH)2].

Ca(OH)2(s) + Cl2(g) CaOCl2(s) + H2O(l)

(slaked lime) (bleaching powder)

Properties: Some of the important properties of bleaching powder are given

below :

Colour and Odour: It is a yellowish-white powder which strongly

smells of chlorine.

Solubility in water: It is soluble in cold water. The unreacted lime

present in it however remains undissolved

Exposure to air: When bleaching powder is exposed to air, it reacts with

atmospheric CO2 to give chlorine gas.

CaOCl2(s) + CO2(g) CaCO3(s) + Cl2(g)

Reaction with acids: Bleaching powder reacts with HCl and H2SO4 to

give off Cl2 gas.

CaOCl2 + 2HCl(dil.) CaCl2(aq) + H2O(l) + Cl2(g)

CaOCl2 + H2SO4(dil.) CaSO4(s) + H2O(l) + Cl2(g)

Uses : Bleaching powder is used :

For bleaching cotton and linen in the textile industry.

For bleaching wood pulp in paper factories and for bleaching washed

clothes in laundry.

As an oxidizing agent in many chemical industries.

For disinfecting drinking water to make it free of germs.

16. Baking Soda: The chemical name of baking soda is sodium hydrogen

carbonate. The formula of baking soda is NaHCO3. Sometimes it is added for

faster cooking.

Manufacturing : It is manufactured by reacting a cold solution of sodium

chloride with carbon dioxide and ammonia.

NaCl + NH3 + H2O + CO2 NaHCO3 + NH4Cl

(sodium hydrogen (ammonium

Carbonate) chloride)

Properties: Some of the \important properties of baking soda are given

below :

State and Solubility: It is white crystalline substance, which is sparingly

soluble in water.

Action of heat: On heating, it decomposes to give sodium carbonate,

and CO2 is liberated.

2NaHCO3 Na2CO3 + CO2 + H2o

(baking soda)

Uses : Some important uses of baking soda are given below :

For making baking powder : Baking powder is a mixture of baking soda

(sodium hydrogen carbonate) and a mild edible acid such as tartaric acid.

When baking powder is heated or mixed in water, the following reaction takes

place :

NaHCO3(aq) + H+(aq) CO2(g) + H2O(l) + Sodium salt of acid

(baking soda) (from tartaric acid)

Carbon dioxide produced during the reaction causes bread or cake to rise

making them soft and spongy.

Baking sodium is also an ingredient in antacids. Being alkaline, it neutralizes

excess acid in the stomach and provides relief.

It is also used in soda-acid fire extinguishers.

IMPORTANT FACTS:

Soda-acid fire extinguishers contain a solution of sodium hydrogen carbonate (baking

soda) and sulphuric acid. When the extinguisher is inverted, sulphuric acid spill and

reacts, with sodium hydrogen carbonate. The reaction produces a large quantity of

carbon dioxide and water. H2SO4 + 2NaHCO3 Na2CO3 + CO2 + H2O

The high pressure of the gas produces a stream of effervescent liquid through the

nozzle. The effervescencing liquid is a mixture of carbon dioxide and water. When the

mixture is direct towards fire, carbon dioxide surrounds the burning. The burning

objects which cuts off the supply of air and put off the fire.

17. Washing Soda: Washing soda is sodium carbonate containing 10 molecules of

water of crystallization i.e., it is sodium carbonate decahydrate. Thus, its

molecular formula is Na2CO3.10H2O.

Anhydrous sodium carbonate (Na2CO3) is generally called soda ash.

Manufacturing: Washing soda is produced from sodium chloride in the

following steps :

(i) A cold and concentrated solution of sodium chloride (brine) is reacted

with ammonia and carbon dioxide to obtain sodium hydrogen

carbonate.

NaCl + NH3 + H2O + CO2 NaHCO3 + NH4Cl

Sodium hydrogen carbonate formed is slightly soluble in water, so it

precipitates out as solid.

(ii) Sodium hydrogen carbonate is separated by filteration, dried and heated.

On heating sodium hydrogen carbonate decomposes to form sodium

carbonate.

2NaHCO3 Na2CO3 + CO2 + H2O

(iii) Anhydrous sodium carbonate is dissolved in water and recrystallised to

get washing soda crystals containing 10 molecules of water of

crystallysation

Na2CO3 + 10H2O Na2CO3.10H2O

(soda ash) (washing soda)

Uses : Some important uses of washing soda are given below :

It is used in glass, soap and paper industries.

It is used in the manufacture of sodium compounds such as borax.

Sodium carbonate can be used as a cleaning agent for domestic purposes.

It is used for removing permanent hardness of water.

KNOWLEDGE BOOSTER:

When washing soda is kept open in the air, the crystals of washing soda lose nine

molecules of water of crystallization to form a monohydrate which is a white powder.

This process is called efflorescence.

Na2CO3.10H2O(s) Na2CO3.H2O(l) + 9H2O(g)

(white powder)

18. Plaster of Paris : It is calcium sulphate hemihydrates. Its molecular formula

CaSO4. ½ H2O.

Preperation : It is prepared by heating gypsum (CaSO4.2H2O) at 373K.

CaSO4.2H2O(s) CaSO4. ½ H2O(s) + 1 ½ H2O

During the preparation of plaster of paris, temperature should be controlled

carefully. Otherwise, anhydrous calcium sulphate (CaSO4) will be formed.

Properties : Some important properties of plaster of paris are given below.

Colour : It is white odourless powder.

Reaction with water : When plaster of paris is mixed with water it

forms a hard mass, and changes to GYPSUM.

CaSO4. ½ H2O + 1 ½ H2O CaSO4.2H2O

Uses :

It is used for setting fractured bones in the right position and in making casts

in dentistry.

It is used in making the surface smooth e.g that of walls, ceiling etc.

In making decorative designs on the ceiling, pillars etc.

In making chalks for writing on the black board.

KNOWLEDGE BOOSTER:

I. Plaster of Paris should be stored in a moisture proof container because the presence

of moisture can cause slow setting of Plaster of Paris by bringing about its hydration.

II. Plaster of Paris is used in hospitals for setting fractured bones in the right position

to ensure correct heating. It keeps the fractures bone straight. This use is based on the

fact that when Plaster of Paris is mixed with water and applied around the fractured

bones and limbs, it sets into hard mass, which keeps the bone joins in a fixed position

19. Are the Crystalline Salts Really Dry?

The water molecules which form part of the structure of a crystal are called

water of crystallization.The salts which contains water of crystallisation are

called hydrated salts. Water of crystallization is the fixed number of water

molecules present in one formula unit of salt.

(i) Copper Sulphate crystals contain 5 molecules of water of crystallisation

in one formula unit and it is written as CuSO4.5H2O.

(ii) Sodium Carbonate crystals contain 10 molecules of water of

crystallisation in one formula unit and it is written as Na2CO3.10H2O.

(iii) Calcium Sulphate crystals contains 2 molecules of water of

crystallisation in one formula unit and is written as Na2CO3.10H2O.

STRUCTURAL QUESTIONS AND ANSWERS

Q.1.You have been provided with three test tubes.One of them contains distilled

water and the other two contain an acidic solution and basic solution,

respectively. If you are given only red litmus paper how will you identify the

contents of each test tube?

Answer: (a) Put the given red litmus paper in all the test tubes, turn by turn. The

solution which turns red litmus to blue, will be a basic solution.

(b) Now put the blue litmus paper obtained above in the remaining two test tubes

one by one. The solution which turns blue litmus paper to red, will be the acidic

solution.

(c) The solution which now effect on any litmus paper will be neutral and hence it

will be distilled water.

Q.2. Why should curd and sour substances not be kept in brass and copper

vessles?

Answer : When acidic substances like curd or other sour substances are kept in

copper or brass vessels, they react to form toxic compounds and make the food stuff

not fit for consumption. So, these substances should not be kept in brass and copper

vessels.

Q.3. Which gas is usually liberated when an acid react with a meta ? illustrate

with an example. How will you test for the presence of this gas?

Answer: Usually hydrogen gas is liberated when a metal reacts with an acid. E.g.

Zn + H2SO4 ZnSO4 + H2

(zinc) (sulphuric (zinc (hydrogen)

Acid) sulphate)

Presence of hydrogen gas can be tested by passing the gas through soap solution and

then bringing a burning candle near the soap bubble filled with the gas. The soap

bubbles bursts and the hydrogen gas burns with a pop sound.

Q.4.) A metal compound reacts with dilute hydrochloric acid to produce

effervescence. The gas evolved extinguish a burning candle. Write a balanced

equation for the reaction if one of the compounds formed is calcium chloride.

Answer. The gas evolved carbon dioxide. Metal compound is calcium carbonate

CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)

(Compoud A) (hydrochloric (calcium (carbon

Acid) chloride) dioxide)

Q.5. Why do HCl, HNO3 etc. show acidic characteristics in aqueous solution

while solutions of compounds like alcohol and glucose do not show acidic

character?

Answer.The acidic character of a substance is due to the presence of hydrogen ions

[H+(aq) ions] in its aqueous solution. HCl, HNO3 etc. show acidic properties because

they produce hydrogen ions when dissolved in water. The solutions of compounds

like glucose and alcohol do not show acidic character because they do not ionize in

water to produce hydrogen ions.

Q.6. Why does an aqueous solution of an acid conduct electricity?

Answer. The aqueous solution of an acid conducts electricity due to the presence of

charged particles called ions in it. For example when hydrochloric acid (HCl) is

dissolved in water, then its aqueous solution contains hydrogen ions [H+(aq)] and

chloride ions [Cl-(aq)]. These ions carry electric current. Therefore, due to the

presence of H+ (aq) ions and Cl-(aq) ions, a water solution of hydrochloric acid

conducts electricity.

Q.7. Why does dry HCl gas not change the colour of the dry litmus paper?

Answer. Dry HCl does not contain H+ ions. That is why it does not change the colour

of dry litmus paper.

Q.8. While diluting an acid why is it recommended that the acid should be added

to water and not water to the acid?

Answer. The process of mixing water to concentrated acid is highly exothermic in

which a large amount of heat is evolved.

(i) When the concentrated acid is added to the water, then the heat is evolved

gradually and easily absorbed by the large amount of water.

(ii) If water is added to concentrated acid then a large amount of heat is evolved

at once. This heat changes some of the water to steam explosively which

can splash the acid on our face or clothes and cause acid burns.

Q.9. How is the concentration of hydronium ions (H3O+) affected when a solution

of an acid is diluted?

Answer. On dilution of an acid solution, the concentration of hydronium ions (H3O+)

per unit volume decreases.

Q.10. How is the concentration of hydroxide ions (OH-) affected when excess

base is dissolved in a solution of sodium hydroxide?

Answer. Concentration of OH- ions per unit volume in the solution increases.

Q.11. You have two solutions, A and B. The pH of the solution A is 6 and pH of

the solution B is 8. Which solution has more hydrogen ion concentration? Which

of these is acidic and which one is base?

Answer. (a) Solution A of lower pH value of 6 has more hydrogen ion concentration.

(b) Solution A oh pH value 6 is acidic and the solution B of pH value 8 is basic.

Q.12. What effect does the concentration of H+(aq) ions have on the nature of the

solution?

Answer. Higher the concentration of H+ ions in a solution, more acidic is the solution.

Q.13. Do basic solution have H+(aq) ions? If yes, then why are these basic?

Answer. Even the basic solutions have hydrogen ions [H+(aq) ions] in them which

come from the ionization of water in which the base is dissolved. They are basic

because the concentration hydroxide ions [OH- ions] in them is much more than the

concentration of hydrogen ions.

Q.14. Under what soil condition do you think a farmer would spread or treat the

soil of his fields with quick lime (calcium oxide) or slaked lime (calcium

hydroxide) or chalk (calcium carbonate)?

Answer. A farmer would treat the soil of his fields with quick (calcium oxide) or

slaked lime (calcium hydroxide) or slaked lime (calcium hydroxide) or chalk (calcium

carbonate) if the soil is too acidic, having a low pH value. All these materials are

bases and hence react with the excess present in the soil and reduce its acidity.

Q.15. What is the common name of the compound CaOCl2.

Answer. Bleaching powder.

Q.16. Name the substance which on treatment with chlorine yields bleaching

powder?

Answer. Calcium Hydroxide [Ca(OH)2].

Q.17. Name the sodium compound which is used for softening hard water.

Answer. Sodium carbonate (washing soda).

Q.18. What will happen if a solution of sodium hydrogen carbonate is heated?

Answer. Sodium carbonate is formed.

Q.19. Write an equation to show the reaction between plaster of paris and water?

Answer. CaSO4. ½ H2O(s) + 1½ H2O(l) CaSO4.2H2O(s)

Q.20. A solution turns red litmus blue, its pH is likely to be

(a) 1

(b) 4

(c) 5

(d) 10

Answer. The solution which turns red litmus blue is basic. Hence its pH should be

greater than 7. Therefore (d) is the correct option.

Q.21. A solution reacts with crushed eggshells to give a gas that turns lime water

milky. The solution contains

(a) NaCl

(b) HCl

(c) LiCl

(d) KCl

Answer. The eggshells are made of calcium carbonate and the gas which turns lime

water milky is carbon dioxide. Carbon dioxide gas can be formed by action of an acid

solution on calcium carbonate (or eggshells). So, the solution contains HCl.

Q.22. 10ml of solution of NaOH is found to be completely neutralized by 8 mL of

a given solution of HCl. If we take 20 mL of the same solution of NaOH, the

amount of HCl solution (the same solution as before) required to neutralize it

will be

(a) 4 mL

(b) 8 mL

(c) 12 mL

(d) 16 mL

Answer: In this case the amount of the same HCl solution required to neutralize,it is

also double. So, the correct option is (d).

Q.23. Which one of the following types of medicines is used for treating

indigestion?

(a) Antibiotic

(b) Analgesic

(c) Antacid

(d) Antiseptic

Answer. ( c) Antacid

Q.24. Write word equations and then balanced equations for the reactions taking

place when

(a) dilute sulphuric acid reacts with zinc granules.

(b) dilute hydrochloric acid reacts with magnesium ribbon.

(c) dilute sulphuric reacts with aluminium powder.

(d) dilute hydrochloric acid reacts with cross fillings.

Answer. (a) The word equation is:

Zinc + Sulphuric acid Zinc sulphate + Hydrogen

The balanced equation will be :

Zn + H2SO4 ZnSO4 + H2

(b) the word equation is :

Magnesium + Hydrochloric acid Magnesium Chloride + Hygrogen

The balanced equation will be:

Mg + 2HCl MgCl2 + H2

(c) The word equation is :

Aluminium + Sulphuric acid Aluminium Sulphate + Hydrogen

The balanced equation will be :

2Al + 3H2SO4 Al2(SO4)3 + 3H2

(d) the word equation is :

Iron + Hydrochloric acid Iron(II) + Chloride + Hydrogen

The balanced equation will be :

Fe + 2HCl FeCl2 + H2

Q. 25.Compunds such as alcohols and glucose also contain hydrogen but are not

categorised asacids. Describe an activity to prove it.

Answer. Only those substances containing hydrogen are considered to be acids which

dissolve in water to produce hydrogen ion [H+(aq) ions]. The hydrogen containing

compounds such as glucose and alcohol are not categorised as acids because they do

not produce hydrogen ions [ H+(aq) ions] when dissolved in water.

Activity: Take 100 mL beaker and place cork in which two nails are fixed, in the

beaker . Now connect the nails to the two terminals of 6 volt battery. Then pour some

glucose in the beaker and switch on.

The bulb does not glow and ammeter does not show any deflection. This shows that

glucose solution do not conduct electricity. So, they are categorised as acids.

Q.26.Why does distilled water not conduct electricity,whereas rainwater does

Answer: Distilled water does not conduct electricity because it does not contain any

ion compounds(like acids,bases or salts) dissolve in it. When rain water falls to the

earth through the atmosphere,is dissolves an acidic gas CO from the air and forms

some carbone acid(H2CO3). Carbonic acid provides some H+(aq)ions and CO32-(aq)

ions to rain water. Due to the presence of these ions,rain water conducts electricity.

Q.27.Why do acids not show acidic behavior in the absence of water ?

Answer. In case of acid water helps in the disssociation to give hydronium ions

(H3O+). In absence of water hydronium ions are not produced. That’s why the acid

show acidic behaviour only in the presence of water.

Q.28. Five solutions A, B, C, D and E when tested with universal indicator

showed pH of 4, 1, 11, 7 and 9 respectively. Which solution is

(i) Neutral

(ii) Strongly alkaline

(iii) Strongly acidic

(iv) Weakly acidic

(v) Weakly alkaline?

Arrange the pH in the increasing order of hydrogen ion concentration.

Answer. (i) Neutral : D(pH = 7)

(iii) Strongly alkaline : C(pH = 11)

(iv) Strongly acidic : B(pH = 1)

(v) Weakly acidic : A(pH = 4)

(vi) Weakly alkaline : E(pH = 9)

Increasing order of hydrogen ion concentration

C(11) < E(9) < D(7) < A(4) < B(1)

Q.29. Equal length of magnesium ribbons are taken in test tubes A and B.

Hydrochloric acid (HCl) is added to test tube A while acetic acid (CH3COOH) is

added to test tube B. In which test tube will the fizzing occur more vigorously

and why?

Answer: Fizzing occurs due to the evolution of hydrogen gas produced by the action

of acid on magnesium ribbon. Fizzing will occur more vigorously in test tube A

because hydrochloric acid is a strong acid containing more hydrogen ions [H+(aq)

ions]. Acetic is a weak acid containing less amount of hydrogen ions and hence

produces slow fizzing.

Q.30. Fresh milk has pH of 6. How do you think the pH will change as it turns

into curd? Explain your answer.

Answer. When the milk turns into curd, its pH will fall below 6 i.e., will become

more acidic. This is because an acid (lactic acid) is produced when milk turns into

curd.

Q.31. A milk man adds a very small amount of baking soda to a fresh milk.

(a) why does shift the pH of the fresh milk from 6 to slightly alkaline

(b) why does milk take a long time to set as curd

Answer. (a) Fresh milk is made slightly alkaline by adding a little of baking soda so

that it may not get sour easily due to the formation of lactic acid in it.

(b) the slightly alkaline milk takes a longer time to set into curd because the lactic

acid being formed during curdling has to first neutralize the alkali present in it.

Q.32. Plaster of paris should be stored in a moisture proof container. Explain

why?

Answer. Plaster f paris absorbs water and set into a hard mass, which makes the

plaster of paris unusable.

Q.33. What is neutralization reaction? Give two examples

Answer. When an acid reacts with a base to form salt and water it is called

neutralization reaction. For example

(i) NaOH + HCl NaCl + H2O

Sodium Hydrochloric sodium water

Hydroxide acid chloride

(base) (acid)

(ii) KOH + HNO3 KNO3 + H2O

Potassium nitric potassium water

Hydroxide acid nitrate

(base) (acid)

Q.34. Write two important uses of washing soda and baking soda?

Answer. Washing soda:

(i) It is used for washing clothes (laundry purposes)

(ii) It is used for softening water.

Baking soda:

(i) It used for preparing baking powder.

(ii) It is used as an antacid.

IMPORTANT NCERT ACTIVITIES

Activity 2.1

AIM : To tst the given samples with the help of red litmus solution, blue litmus

solution, phenolphathalein and methyl orange indicators.

MATERIAL REQUIRED : Samples of hydrochloric acid (HCl), sulphuric acid

(H2SO4), nitric acid (HNO3), acetic acid (CH3COOH), sodium hydroxide (NaOH),

calcium hydroxide [Ca(OH)2], potassium hydroxide (KOH), magnesium hydroxide

[Mg(OH)2] and ammonium hydroxide (NH4OH)

PROCEDURE:

1. Take each of the above solutions in separate test tubes.

2. Test the nature of these solutions by adding a drop of red litmus solution, blue

litmus solution, phenolphathalein and methyl orange indicators. Observe the change

in Colour and Record your Observations:

Sample

solution

Red litmus

solution

Blue litmus

solution

Phenalphathalein

solution

indicators

Methyl

orange

indicator

HCl

H2SO4

HNO3

CH3COOH

NaOH

Ca(OH)2

KOH

Mg(OH)2

NH4OH

No Change

No Change

No Change

No Change

Blue

Blue

Blue

Blue

Blue

Red.

Red

Red

Red

No Change

No Change

No Change

No Change

No change

(Colourless

after

sometime)

Colourless

Colourless

Colourles

Colourless

Pink

Pink

Pink

Pink

Pink

Pink

Pink

Pink

Pink

Yellow

Yellow

Yellow

Yellow

Yellow

(Colourless

after

sometime)

OBSERVATION :

Acidic substances turn blue litmus red. Basic substances turn red litmus blue.

Phenolphthalein remains colourless in acidic substances whereas it becomes pink in

basic substances. Methyl orange becomes pink in acidic substances and yellow in

basic substances.

CONCLUSIONS :

HCl , H2SO4, HNO3 and CH3COOH are acidic in nature while NaOH , Ca(OH)2,

KOH, Mg(OH)2 and NH4OH are basic in nature.

ACTIVITY 2.2

AIM : To test the given samples with help of olfactory indicators, (onion extract).

MATERIAL REQUIRED :

Take finely chopped onions in a plastic bag aloing with some strips of clean cloth,

dilute HCl solution, dilute NaOH solution.

PROCEDURE :

1. Tie up the bag tightly and leave overnight in the fridge.

2. Take two of the cloth strips (which are used for acids and bases) and check their

odour.

3. Keep the cloth stirps on a clean surface and put a few drops of dilute HCl solution

on one strip and a few drops of dilute NaOH solution on the other.

4. Rinse both cloths strips with water and again ckeck their odour.

5. Note your observations.

OBSERVATIONS :

Onion has a characteristics smell. When basix solution, like sodium hydroxide

solution is added to cloth strip treated with onions, then the onion smell cannot be

detected. An acidic solution like hydrochloric acid, however does not destroy the

smell of onions.

CONCLUSIONS :

HCl is acedic in nature and NaOH is basic in nature.

ACTIVITY 2.3

AIM: To test the given samples with the help of olfactory indicators (vanilla

extract).

MATERIAL REQUIRED:

Dilute vanilla essence, dilute HCl, dilute NaOH, two test tubes.

PROCEDURE:

1. Take some dilute HCl solution in one test tube and dilute NaOH solution in another.

2. Add a few drops of dilute vanilla essence to both test tubes and shake well.

3. Shake the test tubes.

4. Note your observations.

OBSERVATION:

Vanilla extract has a characteristic pleasant smell. If a basic is added to vanilla extract,

then we cannot detect the characteristic smell of vanilla extract. An acid substance

however, does not destroy the smell of vanilla extract.

CONCLUSION:

Dilute HCl solution is acidic in nature and dilute NaOH is basic in nature.

ACTIVITY 2.4

AIM: To show that acid reacts with metals to liberate hydrogen gas.

MATERIAL REQUIRED:

Dil.H2SO4 test tube, zinc granules, match stick, candle, delivery tube, stand etc.

PROCEDURE (Case A):

1. Take about 5ml of dilute sulphuric acid in a test tube and add a few tube and ad a

few pieces of zinc granules to it.

2. Note your observation.

OBSERVATION:

It is observed that a brisk reaction takes place at the surface of zinc granules.

CONCLUSION:

This shows that reaction is taking place with the evolution of gas.

PROCEDURE (Case B):

1. Pass the gas being evolved through the soap solution.

OBSERVATION:

The soap bubbles filled with the gas rise up.

CONCLUSION:

This shows that the gas is lighter than soap solution.

PROCEDURE (Case C):

1. Take burning candle near a gas filled bubble.

OBSERVATION:

The bubble bursts and the gas present in it catches fire with pop sound.

CONCLUSION:

This shows that gas is hydrogen.

ACTICVITY 2.5

AIM: To show the reaction of metal with alkali.

MATERIAL REQUIRED:

Granulated zinc metal, test tube, sodium hydroxide.

PROCEDURE:

1. Place few pieces of granulated zinc in the test tube.

2. Add 2ml of sodium hydroxide solution and warm the contents of the test tube.

3. Record the observation.

OBSERVATION:

Zinc metal dissolves in sodium hydroxide and form sodium zincate (Na2ZnO2) and

hydrogen gas (H2).

ACTIVITY 2.6

AIM: To show acid reacts with metal carbonate to liberate carbon dioxide.

MATERIAL REQUIRED:

Two test tubes, label them as A and B, 0.5gm sodium carbonate, 0.5gm sodium

hydrogen carbonate, dilute HCl, lime water [Ca(OH)2].

PROCEDURE:

1. Take two test tubes.

2. Label test tube as A and B.

3. Take about 0.5gm of sodium carbonate (Na2CO3) in test tube A and about 0.5gm of

sodium hydrogen carbonate (NaHCO3) in test tube B.

4. Add about 2mL of dilute HCl to both the test tube.

5. Note your observation.

OBSERVATION:

Acid reacts with metal carbonate and metal hydrogen carbonate to give salt, carbon

dioxide and water.

CHEMICAL REACTION:

Test tube A:

Na2CO3(s) + 2HCl(aq) 2NaCl(aq) + H2O(l) + CO2(g)

Test tube B:

NaHCO3(s) + HCl(aq) NaCl(aq) + H2O(l) + CO2(l)

PROCEDURE:

1. Pass the gas produced in each case through lime water [Ca(OH)2].

2. Note your observation.

OBSERVATION:

We observe that the lime water turns milky.

CONCLUSION:

Lime water turns milky, showing that the gas evolved is carbon dioxide, and it is due

to the formation of white precipitate of calcium carbonate.

Ca(OH)2(aq) + Co2(g) CaCO3(s) + H2O(l)

(Lime water ) (White ppt)

If excess of carbon dioxide gas is passed through lime water, then the white

precipitate formed first dissolves due to the formation of a soluble salt called

hydrogen carbonate, and the solution becomes clear again.

CaCO3(s) + Co2(g) + H2O(l) Ca(HCO3)2(aq)

(white ppt) (Soluble in water)

ACTIVITY 2.7

AIM: To demonstrate neutralization reaction between acid and base.

MATERIAL REQUIRED:

2mL of dilute NaOH, one test tube, two drops of phenolphthalein solution.

PROCEDURE (A) :

1. Take about 2mL of dilute NaOH solution in a test tube

2. Add 2 or 3 drops of phenolphthalein solution and observe the colour of the solution.

OBSERVATION:

The colour of the solution will turn pink.

CONCLUSION:

The solution will turn pink, which shows that it is basic in nature.

PROCEDURE (B) :

1. Add dilute HCl to the above solution drop by drop.

2. Observe the colour change for the reaction mixture.

OBSERVATION:

The pink colour of the solution in the test tubes just disappears. The solution becomes

colourless.

CHEMICAL REACTION:

NaOH + HCl NaCl + H2O

CONCLUSION:

All the sodium hydroxide base taken in the test tube has been completely neutralized

by hydrochloric acid. The colour of the phenolphthalein indicator changes from pink

to colourless because no more sodium hydroxide base is left unreacted in the test tube.

The reaction mixture has become neutral. It is an example of neutralization reaction.

ACTIVITY 2.8

AIM: To study the reaction of metallic oxide with acids.

MATERIAL REQUIRED:

Small amount of copper oxide, a beaker and dilute hydrochloric acid.

PROCEDURE:

1. Take a small amount of copper oxide in a beaker.

2. Observe its colour.

3. Add dilute hydrochloric acid.

4. Observe the change in colour.

OBSERVATION:

The black copper oxide changes to blue-green coloured copper sulphate solution.

CHEMICAL REACTION:

CuO(s) + 2HCl(dil.) CuCl2(aq) + H2O(l)

Black copper blue-green

oxide

CONCLUSION:

Bases react with acids to form salt.

ACTIVITY 2.9

AIM: To show that solution of an acid can conduct electricity.

MATERIAL REQUIRED:

Hydrochloric acid, two nails, cork, 100mL beaker, 6 volt battery, bulb and switch.

PROCEDURE:

1. Fix two nails on the cork.

2. Connect the nails to the two terminals of a 6 volt battery through a bulb and a

switch

3. Place the cork in a 100mL beaker.

4. Now pour some dilute HCl in the beaker.

5. Switch in the current.

6. Note your observation.

OBSERVATION:

The bulb will start glowing.

CONCLUSION:

Solution of acid can conduct electricity.

ACTIVITY 2.10

AIM: To show that glucose and alcohol solutions do not conduct electricity.

MATERIAL REQUIRED:

Solutions of glucose or alcohols, two nails on a cork, 100mL beaker, 6V volt battery, a

bulb and a switch.

PROCEDURE:

1. Fix two nails on a cork and place the cork in a 100mL beaker.

2. Connect the nails to the terminals of a 6V battery through a bulb and a switch as

shown in figure.

3. Now pour some glucose or alcohol solutions, in a beaker.

4. Switch on the current.

5. Not your observation.

OBSERVATION:

Bulb does not glow.

CONCLUSIONS:

Glucose or alcohol solutions do not conduct electricity.

ACTIVITY 2.11

AIM: To show acids do not show acidic behavior in the absence of water.

MATERIAL REQUIRED:

1gm solid NaCl, the dry test tubes, conical flasks, delivery tube, cork, delivery tube,

dry and wet blue litmus paper, concentrated sulphuric acid.

PROCEDURE:

1. Take about 18m solid NaCl in a clean and dry test tube.

2. Add some concentrated sulphuric acid to the test tube.

3. Note the observations.

OBSERVATION:

Concentrated sulphuric acid reacts with sodium chloride to form hydrogen chloride

gas.

PROCEDURE:

1. Test the gas evolved (HCl) successively with dry and wet blue litmus paper.

OBSERVATION:

1. There is no change in the colour of ‘dry’ blue litmus paper.

2. There is change in the colour of ‘moist’ blue litmus paper.

CONCLUSION:

1. Hydrogen chloride does not behave as an acid in the absence of water.

2. Hydro gen chloride gas shows acidic behavior in the presence of water.

ACTIVITY 2.12

AIM: To show mixing of acid in water is an exothermic reaction.

MATERIAL REQUIRED:

One beaker, 10mL water, few drops of concentrated H2SO4.

PROCEDURE:

1. Take 10mL water in a beaker.

2. Add few drops of concentrated H2SO4.

3. Swirl the beaker slowly.

4. Touch the base of the beaker.

5. Note the observation.

OBSERVATION:

There is a rise in temperature.

CONCLUSION:

Dissolution of acid in water is an exothermic reaction.

ACTIVITY 2.13

AIM: To determine the pH of various substances with the help oh pH paper.

MATERIALS REQUIRED:

Saliva (before meal), saliva (after meal), Lemon juice, colourless aerated drink, carrot

juice, coffee, tomato juice, tap water, 1M NaOH, 1M HCl, pH paper.

PROCEDURE:

1. Take pH paper.

2. Add 2-3 drops of various substances on pH paper.

3. Observe the change in colour.

OBSERVATION:

If pH of solution is less than 7 it is acidic and the colour of solution is red for strongly

acidic, light yellow for weakly acidic. If pH = 7, the colour of pH is greenish and if

the colour of pH is greenish blue it is weakly basic. If colour of pH is violet, solution

is strongly basic.

ACTIVITY 2.14

AIM: To determine pH of a various types of sails using paper.

MATERIAL REQUIRED:

One test tube, 5mL water, 2gm soil and pH paper.

PROCEDURE:

1. Put about 2gm soil in a test tube.

2. Add 5mL water to test tube.

3. Shake the contents of the test tube.

4. Filter the contents and collect the filterate in a test tube.

5. Check th pH of this filterate with the help of universal indicator paper

6. Note the observation.

OBSERAVATION:

The pH paper shows different colours in different types of soils.

CONCLUSION:

If pH of soil is less than 7, soil is acidic, equal to 7, soil is neutral and more than 7,

soil is basic.

ACTIVITY 2.15

AIM : To show crystalline salts contain water of crystallization.

MATERIALS REQUIRED:

Crystals of copper sulphate(CuSO4.5H2O), dry boiling tube, Test tube holder, Burner.

PROCEDURE:

1. Take 2gm of CuSO4.5H2O in a dry boiling tube.

2. Heat the crystals.

3. Observe the colour.

OBSERVATION:

1. When copper sulphate crystal is heated , the water is removed and the salt

turns white.

PROCEDURE :

1. Add 2-3 drops of water on the sample of copper sulphate obtained after

heating.

2. Observe the colour.

OBSERVATION :

1. If we moisten the crystals again with water, the blue colour of the crystals

reappears.

CHEMICAL REACTION :

CuSO4.5H2O CuSO4 +5H2O

CONCLUSION :

Crystalline substances have water of crystallization which are lost on heating.

VERY SHORT ANSWER TYPEQUESTIONS

Q.1. What happens chemically when quicklime is added to water?

Ans. Slaked time Ca(OH)2 is formed

CaO(s)+H2O(l) Ca(OH)2(aq)

Q.2. How does the flow of acid rain water in to a river make the survival of

aquatic like in the river difficult ?

Ans . Because releasing of oxygen become difficult.

Q.3. How is the pH of a solution of an acid influenced when it is diluted ?

Ans. The concentration of H+(aq) per unit volume decreases. But over all the pH

of the solution of the acid remains same.

Q.4. Two solutions A and B have pH values of 5 and 8 respectively. Which

solution will be basic in nature ?

Ans. Solution B will be basic in nature .

Q.5. Why does an aqueous solution of an acid conduct electricity ?

]

Ans. The aqueous solution of an acid conducts electricity due to the presence of

charged particles [H+(aq)] in it.

Q.6. How does the concentration of a hydronium ions (H3O+) change when a

solution of an acid is diluted?

Ans . The concentration of a hydronium ions (H3O+)per unit volume decreases when a

solution of an acid is diluted.

Q.7. Which has a higher pH value, a concentrated or dilute solution of

hydrochloric acid ?

Ans .A dilute solution of the hydrochloric acid has a higher pH value than a

concentration solution.

Q.8. What is the colour of Phenol phthalein in acidic solution ?

Ans . Colourless.

Q.9. What is indicator?

Ans . An indicator is a ‘dye’ that changes colour when it is put into an acid or a

base.

Q.10. Name two common indicator.

Ans . Litmus, methyl orange

Q.11. When dilute sulphuric acid is added to metal A gramules, then a gas B is

evolved. When gas B is passed through a soap solution, bubbles are formed .

When a match stick is applied to these soap bubbles, the gas in them burns with

a pop sound .Name the metal A and gas B.

Ans. Metal A; Zinc

Gas B; Hydrogen.

Q.12. What is an olfactory indicator ?

Ans . Those substances whose smell (odour) changes in acidic or basic solutions

are called olfactory indicators.

Q.13. Name two olfactory indicators ?

Ans . Onion extract, vanilla extract.

Q.14. What is the name given to the indicators giving different odours in acidic

and basic medium ?

Ans . Olfactory indicators.

Q. 15. Which gas is evolved when an acid reacts with a metal ?

Ans . H2.

Q.16. Which acid is produced in the stomach ?

Ans . HCl.

Q.17. Is dilution of a concentrated acid or base exothermic or endothermic?

Ans . Exothermic .

Q.18. How is the concentration of hydroxide ions(OH-) affected when excess of

base is dissolved in a solution of sodium hydroxide ?

Ans. On dissolving more sodium hydroxide in the same solution, the concentration

of hydroxide ions(OH-) increases.

Q.19. Three solutions A,B and C have pH values of 5,2 and 11 respectively.

Which of the solution is highly acids ?

Ans . Solution B of pH 2 is highly acidic.

Q.20. Give the equation for the reaction of zinc with sodium hydroxide ?

Ans . 2NaOH +Zn Na2ZnO2 + H2

Sodium zincate

Q.21. Define neutralisation reaction .

Ans . The reaction between an acid and a base to form salt is called neutralization.

Q.22. Two solution A and B have pH values of 9.0 and 3.5 respectively. Which

of these solutions will turn litmus from blue to red and which will turn

phenolphthalein from colourless to pink ?

Ans. (i) Solution B of pH 3.5 will turn litmus from blue to red

(ii) Solution A of pH 9.0 will turn phenolphthalein from colourless to pink.

Q.23. Four solutions A,B,C and D have pH valves of 2,6,8 and 11 respectively.

(a) Which solution is the most acidic ?

(B) Which solution is the most alkaline ?

Ans. (a) Solution A of pH 2 is the most acidic.

(b) Solution D of pH 11 is the most alkaline.

Q.24. Define the term pH.

Ans. It is the defined as the negative logarithm of the hydrogen ion concentration

in the solution.

Q.25. What is universal indicator?

Ans.It is a mixture of a number of indicators which shows different colours at

different pH values.

Q.26. Which acid is injected into our body by a bee sting that causes pain ?

Ans. Methanoic acid

Q.27. As the pH of a solution increases from 7 to 14.

(a) What happens is the OH- ions concentration?

(b) What happens to the H+ ions concentration?

Ans. (a) OH- ions concentration increases.

(b) H+ ions concentration descreases.

Q.28. Solution A gives pink colour when a drop OF Phenolphthalein indicator is

added to it. Solution of B gives red colour when a drop of methyl orange is added

to it. What are types of solution A and B and what type of pH would they have.

Ans. Solution A is basic i.e pH>7.

Solution B is acidic i.e., pH < 7.

Q.29. Write the chemical formula of washing soda.

Ans. Na2CO3.10H2O

Q.30. State whether an aqueous solution of washing soda is acidic or alkaline .

Ans. Alkaline.

Q.31. Write the chemical name of baking soda .

Ans. Sodium hydrogen carbonate.

Q.32. Write the chemical formula of baking soda .

Ans. NaHCO3.

Q.33. Write the chemical name of washing soda.

Ans. Sodium carbonate decahydrate

Q.34. Write the chemical name of Plaster of Paris.

Ans. Calcium sulphate hemihydrates.

Q.35. Write the chemical formula of Plaster of Paris.

Ans. CaSO4. ½ H2O

Q.36 A white chemical compound becomes hard on mixing with proper

quantity of water. It is also used in surgery to maintain joints in a fixed position .

Name the chemical compound .

Ans. Plaster of Paris

Q.37. A compound which is prepared from gypsum has the property of

hardening when mixed with proper quantity of water. Identify the compound.

Ans. Plaster of Paris

Q.38. Write two uses of bleaching powder.

Ans. (i) It is used for disinfecting drinking water to make it free for germs.

(ii) It is used as an oxidizing agent in chemical industries.

Q.39. Write two uses of Plaster of Paris

Ans. (i) It is used for sealing gaps.

(ii) It is used for making casts for statues.

Q.40. Write the chemical name for common salt.

Ans. Sodium Chloride.

Q.41. Write the chemical formula for common salt.

Ans. NaCl

Q.42. Give one example of a salt which equal gives an aqueous solution having

pH equal gives to 7.

Ans. Sodium chloride (NaCl)

Q.43 Give one example each of a salt which equal gives an aqueous solution

having

(a) pH less than 7

(b) pH more than 7

Ans. (a) Ammonium vhloride (NH4Cl)

(b) Sodium carbonate (Na2CO3)

Q.44. Write one important source of common salt.

Ans. Sea water.

Q.45 Write two important uses of common salt.

Ans. (i) It is used for important component of food.

(ii) It is used for the manufacturing of hydrochloric acid.

Q.46. Name two salts that contain water of crystallization.

Ans. (i) CuSO4.5H2O,

(ii)Na2CO3.10H2O.

Q.47. What happens when chlorine is passed through slaked lime ?

Ans. Ca(OH)2 + Cl2 CaOCl2 +H2O.

Q.48. Which compound of calcium is used for sterilization of drinking water ?

Ans. Bleaching powder (CaOCl2)

Q.49. What is the common name of sodium hydrogen carbonate ?

Ans. Baking Soda

Q.50. Name the ingredients of baking powder.

Ans. (i) Sodium hydrogen carbonate.

(ii) Citric acid

Q.51. Which sodium compound is used as an antacid in medicines ?

Ans. Sodium hydrogen carbonate(NaHCO3)

Q.52. What is the commercial name of the compound. Calcium sulphate

hemihydrates ?

Ans. Plaster of Paris.

Q.53. What is the action of hydro – chloride acid on marble ?

Ans. CaCo3(s) +2HCl CaCl2 + H2O + CO2

Q.54. Name the chemicals used in making free-extinguisher.

Ans. Sodium hydrogen carbonate and suphuric acid.

Q.55 What is the range of pH on which out body works ?

Ans. 7.0 to 7.8

Q.56. What is the range od pH of the mouth when tooth decay starts ?

Ans. Below 5.5

Q.57 P and Q are the aqueous solution of sodium carbonate and sodium chloride

respectively. Which of these will turn red litmus blue?

Ans. Aqueous solution of P (sodium carbonate)

Q.58. In addition to sodium hydrogen carbonate, baking powders contain

substance X.Name the substance X.

Ans . substance X. is tartaric acid

Q.59. Name the acid present in sour milk(curd)

Ans. Lactic acid

Q.60. Name the raw material used for the preparation of Plaster of Paris?

Ans. Gypsum, CaSO4.2H2O.

Q.61.How does the flow of acid rain water into a river make the survival aquatic

life in the river difficult?

Ans. When pH of rain water falls below 5.it is called acid rain when this acid rain

flow into the river , the pH of river water falls and survival of aquatic life becomes

difficult.

Q.62. Mention the name of one basic soda.

Ans. Washing Soda(Na2CO3.10H2O)

Q.63.Name the chemical which used for bleaching cotton and linen in the textile

industry.

Ans. Bleaching powder (CaOCl2)

Q.64.Name the chemical which is used for making materials for decoration for

making surfaces smooth.

Ans. Plaster of Paris (CaSO4.½ H2O)

Q.65.The pH of an aqueous solution decreases from 3 to 2 . What will happen to

the nature of the solution?

Ans . The acidic character of the solution will further increase.

Q.66. What is water of crystallization?

Ans. Water of crystallization is the fixed number of water molecules present in one

formula unit of a salt.

Q.67.Name any two chemicals made from common salt (or sodium chloride).

Ans.(i) Sodium hydroxide (Caustic soda)

(ii) Sodium carbonate (Washing Soa).

Q.68.Write and balance the reaction between copper oxide and hydrochloric

acid .

Ans . CuO+2HCl CuCl2 +H2O

Q.69. Write the equation for reaction between sodium hydroxide and zinc.

Ans. 2NaOH + Zn Na2ZnO2 + H2

Q.70. Why is sodium hydrogen carbonate (baking soda) used as an antacid?

Ans.Being basic, sodium hydrogen carbonate(baking soda) neutralizes excess acid in

the stomach and provides relief.

Q.71.How many molecules of water of crystallization (per formula unit) are

present in:

(a) copper sulphate crystals ?

(b) washing soda crystals ?

Ans. (a) 5, (b) 10.

Q.72.Write the name and formula of one salt each which contains:

(a) two molecules of water of crystallization.

(b) five molecules of water of crystallization

Ans. (a) Gypsum, CaSO4.2H2O

(b) Copper sulphate , CuSo4.5H2O.

Q.73.During summer season, a milkman usually adds a very small amount of

baking soda to fresh milk. Give one reason.

Ans.Milk is made slightly alkaline so that it may not get sour easily due to the

formation of lactic acid in it.

Q.74.What conclusion do you get from the fact that metallic oxides react with

acids to give salts and water?

Ans. Metallic oxides are basis in nature.

Q.75.Bases react with non metallic oxide to form salts and water. What does this

tell us about the nature of non-metallic oxide?

Ans. Non-metallic oxides are acidic in nature

SHORT ANSWER TYPE QUESTIONS

Q.1.Name the gas evolved when dilute HCl reacts with sodium hydrogen

carbonate. How is it recognized?

]

Ans.Carbon dioxide gas is evolved when dilute HCl reacts with sodium hydrogen

carbonate. The carbon dioxide gas turns the lime water, milky due is the formation of

a white precipitate of calcium carbonate.

Ca(OH)2(aq) + CO2(g) CaCO3 + H2O(l)

Lime water White ppt.

Q.2.With the help of a chemical equation explain how a soda acid fire

extinguisher helps in putting out a fire.

Answer:In soda-acid fire extinguisher , sodium hydrogen carbonate solution is made

to react with dilute sulphuric acid. The following reaction takes place :

2NaHCO3 + H2SO4 Na2SO4 + 2H2O + 2CO2

Sodium Sulphuric Sodium water carbon

hydrogen acid sulphate dioxide

carbonate

The carbon dioxide gas produced, being behavior then air and non-supporter

of combustion, surround the fire. Hence supply of air is cut off and fire is

extinguished

Q.3.Write the chemical formula for washing soda? How many it be obtained

from baking soda? Name an industrial use of washing soda other than washing

clothes.

Answer: (i) Na2CO3.10H2O

(ii) Step 1. Thermal decomposition of sodium hydrogen carbonate . The dry

crystals of sodium hydrogen carbonate are heated strongly (calcined) when it

decomposes to from anhydrous sodium carbonate (sods ash ) is

2NaHCO3(s) Na2CO3(s) + CO2(g) + H2O (g)

Sodium Anhdrous sodium Carbon water

Hydrogen carbonate

vapour

Carbonatedioxide

Step 2.Recrystallisation of sodium carbonate. The anhydrous sodium carbonate

obtained is step 2 is dissolved in water and then subjected to recrystallisation. As a

result, crystals of washing soda (sodium carbonate dehydrate) are obtained.

Na2CO3(s) 10H2O(l) Na2Ca2.10H2O(s)

(iii)It is used in the manufacture of number of useful products like glass, soap,

paper, borax, caustic soda etc.

Q.4.A baker found that the cake prepared by him is hard and small in size.

Which ingredient has he forgotten to add that would have made the cake fluffy ?

Give reason.

Answer: (i) He has fotgotten to add baking powder.

(ii) During the preparation of cake/bread, sodium bicarbonate liberates CO2

on heating , which makes the cake/bread fluffy.

Q.5. A tarnished copper vessel begins to shine again when rubbed with lemon.

Why?

Answer: Copper vessel is tarnished due to copper oxide layer formed on its surface.

Copper oxide is basic in nature. Lemon is acidic. Hence, when we rub the tarnished

copper vessel with lemon, the basic copper oxide reacts with the acid (citric acid)

present in the lemon to form a salt which is washed with water.

Q.6. How is soda ash obtained from washing soda crystals? Support your answer

by a chemical equation.

Answer: When washing soda crystals are heated strongly, they give up their water of

crystallization. A white powder substance anhydrous sodium carbonate is left behind,

which is called soda ash.

Na2CO3.10H2O Na2CO3 + 10H2O

Q.7. Why is an aqueous solution of sodium carbonate alkaline in nature?

Answer: When sodium is dissolved in water, it undergoes hydrolysis to form a strong

alkali (NaOH) and a weak acid (carbonic acid). In the solution, hydrogen-ion

concentration becomes less than the hydroxide ion concentration. Hence the aqueous

solution of sodium carbonate behaves alkaline.

Na2CO3 + H2O 2NaOH + H2CO3

Q.8. A given compound of sodium is used to remove hardness of water and also

as a reagent in the laboratory. Identify the compound and mention two of its

uses.

Answer. The compound is sodium carbonate Na2CO3.10H2O.

Uses:

(i) In the manufacture of glass.

(ii) In laundries as washing soda.

Q.9. Write the chemical formula for bleaching powder. How is bleaching powder

prepared? For what purpose is it used in paper factories?

Answer.

(i) CaOCl2

(ii) Bleaching powder is prepared by the action of chlorine on dry slaked line at

313K.

Ca(OH)2(s) + Cl2(g) Ca(OCl)Cl(s) + H2O(l)

(iii) It is used as a bleaching agent in paper factories.

Q.10. Describe with chemical equation what happens when

CO2 gas is passed into ammoniacal burette in the solvary process of

manufacturing washing soda.

Answer.

Sodium bicarbonate is formed which being sparingly soluble, separate out the

solution.

NaCl + H2O + NH3 + CO2 NH4Cl + NaHCO3

SUMMARY AND KEY POINTS

1.) Indicators: It is ‘dye’ that changes color when it is put into acid or

a base. It gives different colors in acid and base. The three

2.) Common indicators to test for acids and bases are: Litmus, Methyl

orange and phenophthalein.

The most common indicator used testing acids and bases

in the laboratory is litmus, which can be used in the form

of litmus solution or in the form of litmus paper. It is of

two types : blue litmus and red litmus. Litmus is a natural

indicator, whose neutral colour is purple.

3.) An acid turns blue litmus to red.

4.) A base (or alkali) turns red litmus to blue.

5.) The methyl orange is a synthetic indicator whose neutral colour is

orange.

Methyl orange indicator gives pink color in acid solution.

Methyl orange indicator gives yellow in basic solution.

6.) The phenolphthalein is a synthetic whose neutral colour is

‘colourless’.

Phenolphthalein indicator is colourless in acid solution.

Phenolphthalein indicator gives pink colour in basic solution.

7.) Olfactory indicators: The ‘olfactory’ means relating to the sense

of smell. Those substances whose smell changes in acetic or basic

solutions are called olfactory indicators.

8.) Acids decomposes metal carbonates to liberate carbon dioxide and to form

corresponding salts and water.

Metal carbonate + Acid Salt + Water + Carbon dioxide

9.) Acids react with metal bicarbonates to give out carbon dioxide with

effervescence and forming the corresponding salt and water.

NaHCO3(aq) + HCl(aq) NaCl(aq) + H2O(l) + CO2(g)

10.) When an acid reacts with a base, it forms salt and water. As a

result the acidic properties of the acid disappear. The process is

called neutralization.

The reaction between an acid and a base to give a salt and water is known as

a neutralization reaction.

Example: NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)

11.) Metallic oxides like quick time i.e., calcium oxide (CaO), Copper (II) oxide

(CuO), magnesium oxide (MgO) etc. react with acids to form salt and water.

CaO(s) + 2HCl(aq) CaCl2(aq) + H2O

(salt) (water)

CuO(s) + 2HCl(aq) CuCl2(aq) + H2O

(salt) (water)

12.) General Characteristics Properties of Bases:

13.) Bases have Bitter Taste: Bases possess a bitter taste.

14.) Slipper or Soapy Touch: They possess a slippery touch like soaps.

15.) Action on Litmus Paper: They turn red litmus blue.

16.) Action on Phenolphthalein: They turn phenolphthalein solution pink.

17.) Corrosive Nature: Some bases like caustic soda (sodium hydroxide), caustic

potash (potassium hydroxise) etc. produce a burning sensation on the skin.

18.) Some bases like sodium hydroxide and potassium hydroxide react with active

metals like zinc and aluminium to liberate hydrogen gas with formation of

salt.

2 NaOH + Zn Na2ZnO2 + H2

(sodium hydroxide) (zinc) (sodium zincate) (hydrogen)

2 NaOH + 2 Al + H2O 2NaAlO2 + 3H2

(sodium hydroxide) (aluminium) (water) (sodium aluminate)

19.) When carbon dioxide (CO2) which is a non metallic oxide passed through

lime water that is Ca(OH)2 which is a base, they react to produce salt (CaCO3)

and water.

Ca(OH)2(aq) + CO2(g) CaCO3(s) + H2O(l)

(lime water) (white precipitate)

All bases react with acids to form salt and water, this shows that non-metallic oxides

are acidic in nature.

KEY POINTS:

The acid must always be added slowly to water with constant stirring. If

water is added to a concentrated acid, the heat generated may cause the

mixture to splash out and cause burns.

20.) Acids which are almost completely ionized when dissolved in water are

called strong acids.

Hydrochloric acids(HCl),Nitric acids(HNO3) and sulphuric acids (H2SO4)are

strong acids because they give large around of H+ ions in the solution.

21.) Acids like acetic acid (CH3COOH), formic acid (HCOOH). Carbonic acid

(H2CO3).Phosphoric acid (H3PO4) etc. when dissolved in water dissociate only

partially in the solution. As a result the amount of H+ ions produced in small.

Such acids are called weak acids.

22.) Bases which are almost completely dissociated ionized in their solution are

called strong bases.

Bases like sodium hydroxide (NaOH) and potassium hydroxide (KOH) when

dissolved in water dissociate completely into ions.

23.) Bases like ammonium hydroxide (NH4OH). Calcium hydroxide, Ca(OH)2 etc.

when dissolved in water dissociate only partially to give hydroxide ions. As a

result the amount of OH- ions produced in the solution is small.

Thus, the bases which are partially dissociated/ionized in their aqueous

solution are called weak bases.

24.) Salts: Salts are the ionic compounds consisting of two parts, one part

carrying a positive charge and the other carrying a negative charge. Salt as a

whole is electrically neutral because the number of positive and negative ions

present in the salt are equal.

Or

Salt is a product of neutralization reaction between an acid and a base.

25.) pH of Salts : A salt is formed by the reaction between an acid and a base, so

we should expect that the solution of a salt in water will be neutral towards

litmus. Though the aqueous solutions of many salts are neutral (having pH of

7). Some salts produce acidic or basic solution when dissolved in water. The

pH values of some of the salt solutions are given below:

26.) Depending upon the nature of the acid and base reacting to form the salt,the

salts can be classified in to the following types:

i)Salts of strong acid an strong base

ii.) Salts of weak acid and strong base:

iii.) Salts of strong acid and weak base:

27.) Baking Soda: The chemical name of baking soda is sodium hydrogen

carbonate. The formula of baking soda is NaHCO3. Sometimes it is added for

faster cooking.

KEY POINTS:

Soda-acid fire extinguishers contain a solution of sodium hydrogen carbonate (baking

soda) and sulphuric acid. When the extinguisher is inverted, sulphuric acid spill and

reacts, with sodium hydrogen carbonate. The reaction produces a large quantity of

carbon dioxide and water. H2SO4 + 2NaHCO3 Na2CO3 + CO2 + H2O

The high pressure of the gas produces a stream of effervescent liquid through the

nozzle. The effervescencing liquid is a mixture of carbon dioxide and water. When the

mixture is direct towards fire, carbon dioxide surrounds the burning. The burning

objects which cuts off the supply of air and put off the fire.

28.) Washing Soda: Washing soda is sodium carbonate containing 10 molecules

of water of crystallization i.e., it is sodium carbonate decahydrate. Thus, its

molecular formula is Na2CO3.10H2O.

Anhydrous sodium carbonate (Na2CO3) is generally called soda ash.

KEY POINTS:

When washing soda is kept open in the air, the crystals of washing soda lose nine

molecules of water of crystallization to form a monohydrate which is a white powder.

This process is called efflorescence.

Na2CO3.10H2O(s) Na2CO3.H2O(l) + 9H2O(g)

(white powder)