What do all these acids have in common:

Strong Acids The Formula

Sulphuric acidHydrochloric acidHydrobromic acidHydroiodic acidNitric acidPerchloric acid

H2SO4

HClHBrHIHNO3

HClO4

Acetic acid (vinegar) HC2H3O2

Carbonic acid HCO3

Weak Acid The Formula

Acid:

A substance that ionises (breaks down into ions) and releases H+ ions in an aqueous solution

“aqueous” means: water

Characteristics of Acids: Acids have a sour taste

Acids react with metals (to produce hydrogen gas)

Acids have a pH of 1-6

Acids turn universal indicator yellow, orange or red

Acids turn litmus red

Many are corrosive or poisonous

YOU NEED TO KNOW THREE ACIDS

• Sulfuric acid

• H2SO4

• hydrochloric acid• HCl• Nitric acid

• HNO3

All are Strong AcidsIonise (break down into ions) completely to give off many H+ ions

Weak Acids(only partially breaks down (ionise), gives less H+)

Strong Bases The Formulae

Lithium hydroxideSodium hydroxidePotassium hydroxideRubidium hydroxideCaesium hydroxideBarium hydroxideCalcium hydroxideStrontium hydroxide

LiOHNaOHKOHRbOHCsOHBa(OH)2

Ca(OH)2

Sr(OH)2

What do these bases have in common:

Base:A substance that ionises and releases OH- ions in an aqueous solution

Alkali:

A base that dissolves in water

Characteristics of Bases: Bases usually taste bitter

Bases feel slippery

Bases have a pH of 8 – 14

Bases turn universal indicator blue or purple

Bases turn litmus blue

OH-

BUT AREN’T METAL OXIDES BASES?

• Yes!!!!!!• Metal oxide + water metal hydroxide

• Metal oxides release hydroxide ions in solution

Some bases (VERY FEW) don’t have or produce OH-

Examples include: ammonia NH3

Carbonates (CO3 and HCO3)

***Any chemical which neutralizes an acid can be considered a base

IndicatorsAn indicator is a compound that will change color in the presence of an acid or base

Universal indicator (pH paper) Used for the full pH range

Red Litmus-Turns blue in baseBlue Litmus-Turns red in acid

Phenolphthalein-Turns pink in base

pHpH stands for “potential of Hydrogen” and is a measure of how many H+ ions there are in solution.

The MORE H+ there are, the LOWER the pH will be.

pH ScaleShows the range of H+

concentrations

High H+ concentration Low H+ concentration

Reactions between acids and bases

When an acid and a base react with each other , the characteristic properties of both are destroyed. This is called neutralisation.

This happens because equal amounts of the two substances cancel each others properties and produce two neutral substances (water and a salt).

NOT JUST NaCl !!

Reactions between acids and bases

General formula for acid base reaction:

Acid + Base → Water+ Salt“Salt” means any ionic compound formed from an acid/base reaction

Neutralisation

HCl + NaOH → H2O + NaCl acid base water salt

NeutralisationAnother Example

HCl + KOH → H2O + KCl

H OHKCl

acid base water salt

COMPLETE AND INCOMPLETE NEUTRALISATION

• Any time an acid and base react neutralisation will occur. However, whether the solutions are fully neutralised depends on several factors:

• The pH of both reactants• The concentration of both reactants• The quantity of both reactants

• If any of these factors occur then neutralisation will be incomplete. This means in the solution there will be a metal salt, water and an acid or base.

NAME THE FOLLOWING COMPOUNDS

• CaO• NaOH

• Na2S

• PbCO3

• CuHCO3

• Ag2O

• PbCl2• CuSO4

GENERAL EQUATIONS

• These are all extensions of the acid + base equations

• Acid + metal oxide metal salt + water• Acid + metal hydroxide Metal salt + water

• Acid + Metal carbonate metal salt+ water + carbon dioxide

• Acid + metal hydrogen carbonate metal salt + water+ carbon dioxide

WHAT SALT IS FORMED DEPENDS ON WHAT ACID IS USED

•Hydrochloric acid makes a chloride salt

•Sulfuric acid makes a sulfate salt

•Nitric acid makes a nitrate salt

PREDICT WHAT ACID THESE SALTS WERE MADE FROM

• NaNO3

• CaSO4

• PbCl2• CuCl2• Fe2(SO4)3

• Fe(NO3)2

COMPLETE THE FOLLOWING AS WORD EQUATIONS ONLY

• Hydrochloric acid + Calcium hydroxide

• Sulphuric acid + Lead oxide

• Nitric acid + sodium bi-carbonate

• Silver oxide + sulphuric acid

• Copper carbonate + nitric acid

2. BALANCING WORD EQUATIONS

• Calcium oxide + Hydrochloric acid Calcium chloride + water

• Nitric acid + copper carbonate copper nitrate + water + carbon dioxide

• Hydrochloric acid + lead hydroxide lead chloride + water

• Copper oxide + sulphuric acid copper sulphate + water

• Sodium hydrogen carbonate + nitric acid sodium nitrate + water + carbon dioxide

NCEA 2009

• A student carried out an experiment to neutralise sulfuric acid by adding sodium hydroxide to it.

• Discuss how the student could have determined when the sulfuric acid had been neutralised and what effect adding the sodium hydroxide has on the pH of the solution.

• In your answer include:• • an explanation of neutralisation in terms of an acid-base reaction• • the name of the indicator used• • observations that the student would make as the sodium hydroxide is

added to the acid• • a word and balanced chemical equation for the reaction.

FOUR TWO correct statements (2 a) Eg: Neutralisation is when a base cancels an acid / products are neither acid or base OR Neutralisation is when the solution reaches pH of 7. OR NaOH / base increases the pH. OR NaOH / base neutralises or cancels out the acid. OR Use Universal Indicator / blue and red litmus to detect neutralisation. OR Universal Indicator / blue and red litmus paper will change colour. OR Acid + base salt +water OR Correct word equation. Sodium hydroxide + sulfuric acid sodium sulfate + water

ONE correct simple explanation. (m) Eg: Neutralisation is when the products (salt and water) of the reaction form at pH 7. OR [H+] = [OH–] / H+ + OH- H2O OR At the beginning the solution is red / orange due to the H2SO4 and U.I. At neutralisation the solution turns yellow-green / green. AND equation (m) Correct word equation. Sodium hydroxide + sulfuric acid sodium sulfate + water OR Unbalanced symbol equation. NaOH + H2SO4 Na2SO4 + H2O

Correctly balanced chemical equation. (e) 2NaOH + H2SO4 Na2SO4 + 2H2O AND Correct thorough explanation of neutralisation AND how you use an indicator to observe neutralistion. (2 e) Neutralisation is when a salt and water are produced because the amount of acid = the amount of base. The NaOH increases the pH towards 7 by cancelling out the acid. OR Neutralisation is when the products of the reaction are pH 7 and (as the amount of H30

+ = the amount of OH-) the amount of acid equals the amount of base (when pH = 7 = [H30

+][OH–]). AND At the beginning the solution is red due to the H2SO4. At neutralisation it is yellow-green / green due to the Na2SO4 and H2O (or no H2SO4) present. OR Explains clearly how they would ascertain neutralisation using an appropriate indicator, eg. Add a few drops of Universal Indicator solution. Monitor colour changes as reaction proceeds: red in acid yellow-green / green when neutral.

Sufficiency for Q4 2 a = A 2 m = M 3 e = E

NCEA 2006

• The pH values of three substances are given below: • Hydrochloric acid pH = 1• Potassium carbonate solution pH = 9• Sodium hydroxide solution pH = 14• (a) When Universal Indicator solution is added to each of these substances,

what colour would result?• (i) Hydrochloric acid __________________• (ii) Potassium carbonate solution __________________• (iii) Sodium hydroxide solution __________________• Potassium carbonate solution is added slowly to the hydrochloric acid (without

indicator) in a beaker until no further change is seen. • (b) (i) Describe what you would see happening when potassium

carbonate is added to the acid.• (ii) Write a balanced chemical equation for the reaction between

potassium carbonate and hydrochloric acid.

4 (a)(i) (ii) (iii)

red green / blue blue / purple

2 out of 3 correct.

4(b)(i) Bubbles form. Bubbles form.

4(b)(ii) K2CO3 + 2HCl 2KCl + CO2 + H2O

3 correct formulae required.

All 5 formulae correct, but equation not balanced.

As in evidence column.

In another experiment, sodium hydroxide solution is added slowly to the hydrochloric acid to which Universal Indicator solution has been added.

(c) Describe how the colour of the Universal Indicator solution changes as the sodium hydroxide solution is added. Discuss how the colour changes relate to the substances present in the solution. Use the substances from the key list.

Key list of substances

water

sodium chloride

sodium hydroxide

hydrochloric acid

At the beginning:

When the acid is neutralised:

When further sodium hydroxide is added:

At the beginning – red due to HCl (acidic) at neutralisation – yellow /

green due to NaCl and H2O (or no HCl) present

beyond neutral point – blue with NaCl and NaOH present (basic).

red yellow / green blue / purple described.

As for Achievement, PLUS species / acidity identified at two points, eg: red (due to the acid) yellow / green blue / purple (as now

basic).

As for Achievement PLUS species identified at three of the points. beginning red HCl Neutral yellow / green

NaCl + H2O beyond blue / purple

NaOH.

NCEA QUESTION

• HCl is added to a solution of sodium hydroxide. The reaction takes place but complete neutralisation did not occur. Discuss three things that could have lead to this.

TRY THESE – IN WORDS AND THEN BALANCED CHEMICAL EQUATIONS

• Hydrochloric acid + potassium hydroxide• Sulfuric acid + calcium oxide• Hydrochloric acid + potassium hydroxide• Sulfuric acid + sodium hydroxide