Notes Salts (Chemistry)

8/12/2019 Notes Salts (Chemistry)

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Use of salts;

I tem Use Example

Food preparation

FlavorMonosodium glutamate (MSG)

Sodium chlori de

Preservatives

Sodium chlor ide - salted fi sh

Sodium benzoate - sauce

Sodium ni tr ite - processed meat, burger

Baking powder Sodium hydrogen carbonate

AgricultureNitrogen fertilizers

Potassium nit rate

Sodium nitr ate

PesticideCopper( I I ) sulphate

I ron(I I ) sulphate

Medicine

Reduce stomach acidic

(gastric)

Calcium carbonate

Calcium hydrogen carbonate

Sniff salt (fainted) Ammonium carbonate

Plaster of Paris (cementto support broken bone)

Calcium sulphate

A. Preparation of SaltThe procedure of preparation salt depends to the type of salt.

a. Insoluble saltis prepared through precipitation reaction.

b. Soluble saltis prepared by one of these reactions;

i. Acid and alkaliii. Acid and metal oxide

iii. Acid and metal carbonateiv. Acid and reactive metal

Yellow precipitate ofPbI2

Yellow crystals formed whenthe water is cooled down.

Yellow precipitatedissolves in hot water

PbI2are also solublein hot water.


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a. Insoluble Salts

i. Preparing Insoluble Salts1. Insoluble salts can be prepared through precipitationreactions or double decomposition reactions.

2. Precipitation or double decomposition reaction involves;

- two aquoues solutions/soluble saltswere mix together- one of the solutions contains the cationsof the insoluble salt.

- one of the solutions contains the anionsof the insoluble salt.- the ions of the two aqueous solutions above interchangeto produce two new compound

which is insolublesalt or precipitate, and aqueous solution.

- the precipitate produced is obtained by filtration. The residue left in the filter paper is the

insoluble salt. The filtrate is soluble salt.- the residue/precipitate (insoluble salt)then rinsed with distilled water to remove any other

ions as impurities.

Na+ Na+

NO3-NO3

-

PbCl2

Pb2+

ions combined

with Cl-ions to form

white precipitate

Na+ions and NO3

-ions do not

take part in the reaction andare free to move in the solution

Ionic equation: Pb2+ + 2Cl- PbCl2

Anion

(Non-metal ion)

Cation

(Metal ion)nn mm


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Chemical and ionic equations

Chemical equation : MX(aq) + NY(aq) MY(s) + NX(aq)solution solution precipitate solution

Ionic equation : M+(aq) + Y

-(aq) MY(s)

Study this reaction carefully

In the formation of the precipitate of barium sulphate, BaSO4, the chemical equation can be written:

BaCl2(aq) + Na2SO4 (aq) BaSO4(s) + 2NaCl (aq)

Ions Ba2+ + Cl- + Na+ + SO42-BaSO4 + Na+ + Cl-

Ionic equation : Ba2+

+ SO42-

BaSO4

(shows the ions that take part in the reaction to form precipitate/insoluble salts)

More examples;

Insoluble Salt Ions Ionic equation

ZnCO3 Zn2+

, CO32-

Zn2+

+ CO32-

ZnCO3

AgCl Ag+

, Cl-

Ag+

+ Cl-

AgCl

BaSO4 Ba2+

, SO42-

Ba2+

+ SO42 BaSO4

PbCl2 Pb2+

, Cl- Pb

2+ + Cl

- PbCl2

PbSO4 Pb2+

, SO42-

Pb2+

+ SO42-

PbSO4

CaCO3 Ca2+

, CO32-

Ca2+

+ CO32-

CaCO3

Glass rod

Residue/precipitate(Insoluble salt)

Filtrate

(Soluble salt)

Mixture of solutions

Filter funnel

Filter paper

Retort stand


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ii. Preparation and purification of insoluble salts

Preparation of Plumbum(I I ) iodide

Chemical equation : Pb(NO3)2(aq) + 2KI (aq) PbI2(s) + 2KNO3(aq)

Ionic equation : Pb2+

(aq) + 2I-(aq) PbI2(s)

Step 1: Preparation

1. 20 cm3lead(II) nitrate 0.1 mol dm

-3solution is measured with measuring cylinder 50 ml,

and poured into a beaker.

2. 20 cm3potassium iodide 0.1 mol dm-3solution is measured with measuring cylinder 50 mland poured into a beaker contains lead(II) nitrate solution.

3. The mixture is stirred with a glass rod. A yellow precipitate is formed.

4. The mixture is filtered to obtain the yellow solids of lead(II) iodide as the residue.

Glass rod

Precipitate of lead(II) iodide

(yellow)

Sodium nitrate solution

Mixture of solutions

Filter funnel

Filter paper

Retort standBeaker

+

20 cm

Lead(II) nitrat

0.1 mol dm-3

20 cm

potassium iodide

0.1 mol dm-3


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Step 2: Purification

5. The residue is rinsed with distilled water to remove other ions in it.

6. The yellow solid is dried by pressing between two pieces of filter paper.

EASY LAH !

Precipitate of lead(II)

iodideFilter paper

Glass rodDistilled water

Precipitate of lead(II)

iodide


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b. Soluble Salt

i. Preparaing Soluble Salt

- Sodiumsalts

-

Potassiumsalts Acid + alkali

salts + water- Ammoniumsalts

Soluble Salts

Acid + metal oxide salts + water

- Others salts Acid + reactive metal salts + hydrogen gas

Acid + metal carbonate salt + water + carbon dioxide

Notes: Reactive metal is magnesium, aluminium, and zincUnreactive metal is iron, lead, silver

a. Sodium, potassium or ammoniumsalts prepared from acid and alkalireaction.

Salt Alkali Acid Chemical equation

NaCl NaOH HCl NaOH + HCl NaCl + H2O

K2SO4 KOH H2SO4 2KOH + H2SO4 K2SO4+ 2H2O

NH4NO3 NH3/NH4OH HNO3 NH3+ HNO3 NH4NO3+ H2O

CH3COONa NaOH CH3COOH NaOH + CH3COOH CH3COONa + H2O

Note: To prepare the above salts, titration techniqueis use.

b. Soluble salt (except sodium, potassium and ammonium salt) is prepared using these methods

- Acid and metal- Acid and metal oxide

- Acid and metal carbonate

Name of Salt Acid that must beused

Substance that can be use to react with acid

Metal Metal oxide Metal carbonate

ZnCl2 HCl Zn ZnO ZnCO3

Mg(NO)3 HNO3 Mg MgO MgCO3

CuSO4 H2SO4 CuO CuCO3

Pb(NO3)2 HNO3 PbO PbCO3


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Write a chemical equation for each experiment above.

Remember this notes ok1. Metal that is lessreactivefrom hydrogen such as copper, lead and

silver/argentum didnotreact with dilute acid.

2. Metal, metal oxide and metal carbonate above is a solid that cannot dissolves inwater, hence during reaction that solid must be added excessively to make sure

all hydrogen ions in acid is completely reacted. Excess solid can be expelling

through filtration.3. Impure soluble salt can be purified through crystallizationprocess.

ii. Preparation and purification of soluble salts

A. Preparing soluble salt thr ough reaction between acid and alkal i.

Preparation of Soluble Sodium, Potassium and ammonium SaltsSoluble salts of sodium, potassium and ammonium can be prepared by the reaction between an

acid and alkali.

Acid (aq) + alkali (aq) Salt (aq) + Water (l)

Procedure :

Using pipette, 25 cm3of alkali solution is measured andtransferred into a conical flask.

Two drops of phenolphthalein are added to the alkali solution.

Dilute acid is place in a burette. The initial reading is recorded.

Acid is added slowly into the alkali solution while shakingthe conical flaks, until the pink solution turn colourless.

The final reading of the burette is recorded.

The volume of acid added, V cm3is calculated.

The experiment is repeated by adding V cm3of acid to

25 cm3of alkali solution in a beaker without using

phenolphthalein as an indicator.

The mixture is transferred into a evaporating dish.

The mixture is heated until saturated and the saturated solutionis allowed to cool at room temperature.

Salt crystals formed are filtered and rinsed with a little of cold distilled water.

Salt crystals are dried by pressing it between filter papers (or in oven)

The reaction between acid and alkali is known as what pr ocess?

Refer to acids and bases notes ok. Dont worry Ill help you.!

Ki ta bukan along kita cuma nak tolong.


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Example: Prepar ing sodium chloride

Step 1:Preparation (Titration)

1. 25.0 cm3sodium hydroxide solutions is pipette into conical flask.

2. Two drops of phenolphthalein indicator are added into conical flask. The colour of solution isrecorded.

3. A 50 cm3burette is filled with hydrochloric acid. The initial burette reading is recorded.

4. Hydrochloric acid is added gradually from a burette into conical flask and swirling the conical

flask.5. Titration is stopped when phenolphthalein changes from pink to colourless. The final burette

reading is recorded.6. The volume of hydrochloric acid used is calculated.7. The experiment is repeated by adding hydrochloric acid (known volume) to 25.0 cm3sodium

hydroxide in a beaker without using phenolphthalein.

Step 2: Preparation (Crystallization)

Bunsen burner

Evaporating dishSalt solution

Retort

stand

Burette

Hydrochloric acid

Conical flask

25 cm NaOH + phenolphthalein

indicator


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8. The mixture is transferred into a evaporating dish.9. The colourless solution is slowly heated/evaporated until its saturated or to about one-third

(1/3) of the original volume.

10.The saturated solution is then cooled to allow crystallization to occur.


10. The white crystals formed are then filtered, rinsed with a little distilled

water and dried by pressing between filter paper.

Note: Phenolphthaleinindicator is used at the beginning of the experiment to determine the volume

of hydrochloric acid that is required to react completely with 25 cm3of sodium hydroxide.

However experiment is repeated without using phenolphthalein so that the salt prepared will

not contaminated by the indicator.

Glass rodDistilled water

Copper(II) sulphate

Filter funnel


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B. Preparing soluble salt through reaction between acid

i. Metal oxide. ii . Metal ii i. Metal carbonate

Procedure To Prepare a Soluble Salt (not Na, K or NH4+)

50 cm3of acid is measured using a measuring cylinder and poured into a beaker. The acid isheated slowly.

Using a spatula, metal / metal oxide / metal carbonate powder is added a little at a time whilestirring the mixture with a glass rod.

The addition of the solid powder is stopped when some solids no longer dissolve anymore. (thesolid is excess and all the acid is completely neutralised by the solid)

The mixture is filtered to remove the excess solid powder.

The filtrate is transferred to an evaporating dish.

The filtrate is heated until saturated. (The filtrate is evaporated to about one-third (1/3) of theoriginal volume)

The saturated solution is then allowed to cool to room temperature and the salt crystals areformed.

The crystals are filtered and rinsed with a little cold distilled water.

Salt crystals are then dried by pressing it between filter papers.

Heating

AcidPowder

of :

Metal oxide

Metal carbonateMetal

Excess of solid powder

Filtrate (Salt solution)

Heating

Saturated solution

Crystals

Filtrate


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Example: Prepar ing copper(I I ) sulphate

(Sulphur ic acid and copper( I I ) oxide powder)

Step 1: Preparation

1. 50 cm3sulphuric acid 0.1 mol dm

-3is put in a beaker and is heated.

2. Using spatula copper(II) oxide powder is added a little at a time to the hot sulphuric acid whilestirring continuously with glass rod.

3. The addition of copper(II) oxide is stopped when solids powder remain undissolved.

4. The mixture is filtered to remove the excess copper(II) oxide.5. The filtrate is transferred to an evaporating dish.

Glass rod

Reactant mixture

Excess copper(II) oxide

Copper(II) sulphate solution

xxxxxxxxxxxxxxxx

Copper(II) oxide

Glass rod

Beaker

Wire gauze

50 cm3sulphuric acid 0.1 mol dm

-3

Tripod Bunsenburner

Spatula

Stir


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6. The filtrate is slowly heated/evaporated until its saturated, or to about one-third (1/3) of theoriginal volume.

7. The saturated solution is then allowed to cool to room temperature.


8. The crystals are filtered and rinsed with a little cold distilled water.

9. Salt crystals are then dried by pressing it between filter papers.

REMEMBER. THIS NOTES OK

Unreactive metal such as lead (Pb), copper (Cu), and silver (Ag)cannot reactwith dilute asid. So to prepare salt contains lead ions (Pb2+), copper ions (Cu2+)

or silver ions (Ag+), we must use either oxide powderor carbonate powderonly.

Example: CuO + H2SO4 CuSO4 + H2O (ok)

CuCO3 + H2SO4 CuSO4 + H2O + CO2 (ok)

Cu + H2SO4 no reaction (not ok)

Glass rod

Distilled water

Copper(II) sulphate

Bunsen burner

Evaporating dish

Copper(II) sulphate

solution


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B. Physical Characteristics of Crystals.

A salt is made upof positive and negative ions. When these ions are packed closely

with a regularand repeated arrangementin an orderly manner, a solid with

definite geometry known as crystal latticeis formed.

All crystals have these physical characteristics:

a) Reqular geometry shapes, such as cubic or hexagonal.b) Flat faces, straight edges and sharp angles.c) Same angle between adjacent faces.d) All crystals of the same salt have the same shape although the sizes may be different.

Start to memorize the solubi li ty of a salt in water OK.

I t wi ll help you a lot to better understand thi s chapter .

KNOWLEDGE I S POWER

The solubility of a salt in water depends on the types of cationsand anionspresent.

Salt Solubility in water

Sodium, potassium andammonium salts(Na

+, K

+,NH4

+)

All are soluble

Nitratesalt (NO3-) All are soluble

Chloridesalt (Cl-)

All chloridesalts are solublein water exceptPbCl2, AgCl andHgCl2

Sulphatesalt (SO42-

) All sulphatesalts are solublein water except

PbSO4, BaSO4andCaSO4

Carbonatesalt (CO32-

) All carbonate salts are insolubleexcept

Na2CO3, K2CO3 and(NH4)2CO3


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The table shows the colour of different cations in the solid form or in aqueous solution

Observation Inference

Blue solution Ion copper (Cu2+

) present

Pale green solution Ion Iron(II) Fe2+

present

Yellow/Yellowish-brown/brown solution

Ion Iron (III) Fe3+

present

Green solid Hydrated Fe2+

, CuCO3

Brown solid Hydrated Fe3+

salt

White solidSalts of Na

+, K

+,NH4

+, Mg

2+, Ca

2+Al

3+, Zn

2+, Pb

2+(If the anions

are colourless

Colourless solution Na+, K

+,NH4

+, Mg

2+, Ca

2+, Al

3+, Zn

2+, Pb

2+

The table shows the solubility of different types of salts in water

Compounds Solubility in water

Sodium saltsPotassium saltsAmmonium salts

All are soluble

Nitrate saltsAll are soluble

Chloride saltsAll are soluble except AgCl, HgCl and PbCl2(soluble in hot water)

Sulphate saltsAll are soluble except BaSO4, PbSO4and CaSO4

Carbonate salts All are insoluble except sodium carbonate, potassium carbonate andammonium carbonate


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2. Tests for gases

Gases are often produced from reactions carried out during laboratory tests on salts. By identifying the gasesevolved,it is possible to infer the types of cations and anions that are present in a salt.

The table shows the test and the result of different gases

Gas Test Result

Oxygen gas, O2Test with a glowing woodensplinter

Wooden splinter is rekindled /lighted

Hydrogen gas , H2Test with a lighted woodensplinter

Gas explodes with a pop sound

Carbon dioxide gas , CO2Bubble the gas produced intolime water

Lime water turns milky

Ammonia gas, NH3Test with moist red litmuspaper

Moist red litmus paper turns blue

Chlorine gas, Cl2Test with moist blue litmuspaper

Moist blue litmus paper turns red and thenturns white

Hydrogen chlorine gas , HClTest with a drop ofconcentrated ammonia NH3solution

Dense white fumes

Sulphur dioxide gas , SO2

Bubble the gas produced intopurple acidified potassiummanganate (VII), KMnO4solution

Purple acidified potassium manganate(VII),KMnO4solution decolourises

Nitrogen dioxide gas , NO2Test with moist blue litmuspaper

moist blue litmus paper turns red


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3. Action of heat on salts

Effect of heat on carbonate salts

Carbonaate saltColour of saltbefore heating

Colour of residueEffect on lime water

Hot cold

Copper (II)carbonate, CuCO3

Green powder Black powder Black powderThe gas liberated turnslime water milky/chalky

Zinc carbonate ,ZnCO3

White solid Yelow solid White solidThe gas liberated turnslime water milky/chalky

Lead(II) carbonate,PbCO3

White solid Brown sold Yelow solidThe gas liberated turnslime water milky/chalky

Sodium carbonate,Na2CO3

White solid White solid White solid No change

Calcium carbonate,CaCO3

White solid White solid White solidThe gas liberated turnslime water milky/chalky

Potassiumcarbonate, K2CO3

White solid White solid White solid No change

Magnesiumcarbonate, MgCO3

White solid White solid White solidThe gas liberated turnslime water milky/chalky

Effect of heat on nitrate salts

Nitrate SaltColour of saltbefore heating

Colour of residueTest on gases liberated

Hot cold

Copper (II) nitrate,Cu(NO3)2

Blue solidBlackpowder

Blackpowder

A brown gas that turns blue litmuspaper red is liberated.The gas liberated also ignites aglowing splinter

Zinc nitrate,Zn(NO3)2

White solidYellowsolid

White solid

A browan gas that turns blue litmuspaper red is liberated.The gas liberated also ignites aglowing splinter

Lead(II) nitrate,

Pb(NO3)2 White solid Brown solid

Yellow

solid

A browan gas that turns blue litmuspaper red is liberated.

The gas liberated also ignites aglowing splinter

Sodium nitrate,NaNO3

White solid White solid White solidA colourless gas that rekindles aglowing splinter is liberated

Calcium nitrate,Ca(NO3)2

White solid White solid White solid



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Potassium nitrate,KNO3

White solid White solid White solidA colourless gas that rekindles aglowing splinter is liberated

Magnesium nitrate,Mg(NO3)2

White solid White solid White solid


Iron(II) nitrate,Fe(NO3)2

Pale Greensolid

Pale Greensolid

PaleGreensolid


Iron(III) nitrate,Fe(NO3)3

Brown solidReddish-Brown solid

Reddish-Brownsolid


The table shows the comparison of the effect of heat on carbonate and nitrate salts

Metal Effect of heat on carbonate salt Effect of heat on nitrate salt

PotassiumSodium

Are not decomposed by heat Decompose to nitrite salt and oxygen gas.

CalciumMagnesiumAluminiumZincIronTinLeadCopper

Decompose to metal oxide andcarbon dioxide gas.

Decompose to metal oxide, nitrogen dioxidegas and oxygen gas.

MercurySilverGold

Decompose to metal, carbondioxide gas and oxygen gas.

Decompose to metal , nitrogen dioxide gasand oxygen gas.

Most sulphate salts are not decomposed by heat. Only a few sulphate such as iron(II) sulphate,zinc sulphateand copper sulphate decompose to sulphur dioxide or sulphur trioxide gas when heated.

All chloride salts are stable when heated except ammonium chloride. Ammonium chloride sublimes anddecomposes to produce ammonia gas and hydrogen chloride gas.

The table shows the deduction of the types of ion present based on the gas produced

Type of gas produced Type of ion present(anion)

CO2 Carbonate ion (CO32-

) present except Na2CO3and K2CO3

O2 Nitrate ion (NO3-) present

NO2 Nitrate ion (NO3-) present except NaNO3and KNO3

SO2 Sulphate ion (SO42-

) present

NH3 Ammonim ion (NH4+) present


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Tests for anions

Reagent / Condition Observation Anion Ionic Equation (if any)

2 cm3the unknown solution +

dilute hydrochloric acid / nitricacid / sulphuric acid pourinto a test tube gas liberatedis immediately bubbled throughlime water.

Effervescence.

Colourless gasturns lime watermilky.

CO32-

ion CO32-

+ 2H+ CO2 +

H2O

2 cm3

of nitric acid + 2 cm3

ofthe unknown solution pourinto a test tube +2 cm

3

silver nitrate solution

White precipitateis formed.

Cl-ion Ag

+ + Cl

- AgCl

2 cm3of dilute hydrochloricacid / nitric acid +2 cm

3of the

unknown solution pour intoa test tube +2 cm

3of

barium chloride / barium nitratesolution shake well

White precipitateis formed.

SO42-

ion Ba2+

+ SO42 -

BaSO4

2 cm3of the unknown solution

pour into a test tube2 cm

3of dilute sulphuric acid +

2 cm3of iron(II) sulphate

solution shake well.

Then drop carefully and slowlya few drops of concentratedsulphuric acid along the side ofa slanting test tube into themixture without shaking it.

Brown ring isformed at theboundarybetween theconcentrated

H2SO4(top layer)and aqueoussolution of themixture (bottomlayer)

NO3-ion -


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Tests for cations

Confirmatory Test for Fe2+, Fe3+, Pb2+, NH4+Ions

Confirmatory Test for Fe2+

Reagent Observation Conclusion

Potassiumhexacyanoferrate(II) solution

Pale blue precipitate Fe2+

ion is present

Dark blue precipitate Fe3+

ion is present

Potassiumhexacyanoferrate(III) solution

Dark blue precipitate Fe2+

ion is present

Greenish-brown solution Fe3+

ion is present

Potassium thiocyanatesolution

Pale red colouration Fe2+

ion is present

Blood red colouration Fe3+

ion is present

Confirmatory Test for Pb2+

Method Observation Ionic Equation

Using aqueous solution of chloride- 2 cm

3of any solution of Cl

-+

2 cm3of any solution of Pb

2+

dilute with 5 cm3of distilled water

heat until no further change occursallow the content to cool to roomtemperature using running water fromthe tap

- A white precipitate isformed

When heateddissolve inwater to form colourlesssolution

When cooledwhiteprecipitate reappear

Pb2+

+ 2Cl-

PbCl2

Using aqueous solution of iodide- 2 cm

3of any solution of I

-+

2 cm3

of any solution of Pb2+

dilute with 5 cm

3of distilled water

heat until no further change occursallow the content to cool to roomtemperature using running water fromthe tap

- A yellow precipitate isformed

When heateddissolve inwater to form colourlesssolution

When cooledyellowprecipitate reappear

Pb2+

+ 2I- PbI2

Confirmatory Test for NH4+

Method Observation

2 cm3of any solution of NH4+ + 2 cm3ofNaOH / KOH / Ca(OH)2 heat put apiece of moist red litmus paper at themouth of the test tube

- Moist red litmus paper turns blue

Reaction with Nesslers Reagent

2 cm3of any solution of NH4

+ + 2 cm

3of

Nesslers Reagent shake well

- A brown precipitate is formed


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Reaction of Cations With NaOH

Pb2+ Zn2+ Al3+ : White precipitate dissolves/larut in excess NaOHCa2+ Mg2+ : White precipitate insoluble/tidak larut in excess NaOH

Cations

+ NaOH (aq)

Precipitate producedNo precipitate

White precipitate Coloured precipitate

Green Blue Brown

Fe+

Cu+

Fe+

NH4+

K+

Na+

Dissolve in excessNaOH (aq) to form

colourless solution

Sodium hydroxide solution is pouredslowly into 2 cm

3of the solution to be

tested in a test tube, until in excess.

Insoluble inexcessNaOH (aq)

NH3gas produced

warm

Zn+

Al+

Pb+

Ca+

Mg+

Easylah


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Reaction of Cations With NH3

Zn2+ : White precipitate dissolves/larut in excess NH3Pb2+ Al3+ Mg2+ : White precipitate insoluble/tidak larut in excess NH3

Cations

Precipitate producedNo precipitate

White precipitate Coloured precipitate

Green Blue Brown

Fe+

Cu+

Fe+

NH4+

K+

Na+

Aqueous ammonia solution is pouredslowly into 2 cm

3of the solution to be

tested in a test tube until in excess.

NH3gas produced

warm

Zn+

Al+

Pb+

Ca+

Mg+

Easylah

+ NH3(aq)

+ excessNH3(aq)

Dark bluesolution

Dissolve in excessNH3(aq) to formcolourless solution

Insoluble in

excess NH3(aq)


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Zn2+ion is the only cation that form white precipitate and dissolvesinboth excess NaOH and NH3solutions.

Mg2+

ion is the only cation that form white precipitate and insoluble inboth excess NaOH and NH3solutions.

Ca2+

ion in the only cation that form white precipitate in NaOH

solutions, but no precipitate in NH3solution.

Fe2+

, Fe3+

and Cu2+

ions is easy to spot because the ions shows

coloured precipitate.

Pb2+

ion and Al3+

ion form white precipitate and dissolvesin excess

NaOH

solution, but insolublein excess NH3solutions.

Example: lead(II)nitrate solution and aluminiumnitrate solution

Sodium sulphate solution is added slowly into 2 cm3of the solution to be tested in atest tube.

If a white p recipi tateis formed, then then the solution tested is lead(II) nitrate.If no change occurs, then the solution tested is aluminiumnitrate.

Based from the observation, I can conclude that

How to differentiate between Pb2+and Al3+?

A chemical tests can be carried out inthe laboratory to differentiate between

Pb2+and Al3+.

(Please refer to Confirmatory Test forPb2+, in ealier notes).


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Example 1:

Describe chemical tests that can be carried out in the laboratory to differentiate between

(a) lead(II) nitrate solution and aluminium nitrate solution

Sodium sulphate solu t ion is added slowly in to 2 cm3of the solu tion to be tested in a test tube.

If a white precipi tate is form ed, then then the so lution tested is lead(II) ni trate.

I f no change occu rs, then the solu t ion tested is alumin ium ni t ra te.

(b) aluminium nitrate solution and zinc nitrate solution

Aqueous ammonia solu t ion is poured slowly in to 2 cm3of the solu t ion to be tested in a test tub e

unti l in excess.

I f a whi te precip i ta te that d isso lves in excess aqueous ammo nia solu t ion is form ed, than the

solut ion tested is zinc nitrate.

I f a whi te precip i tate that is inso lub le in excess aqueous ammonia solu t ion is formed, than the

solu t ion tested is alumin ium ni t ra te.

(c) ammonium chloride solution and potassium chloride solution

Nesslers Reagent is added to 2 cm3of the solutio n to be tested in a test tube.

I f a brown precip i ta te is form ed, then the so lu t ion tested is ammon ium chlor ide.

I f no change occurs, then the solu t ion tested is potassium chlor ide

(d) iron(II) sulphate solution and iron(III) sulphate solution

Potassium hexacyano ferrate(II) solu tion is pour ed into 2 cm3of the solu t ion to be tested in a

test tub e.

If a dark blue pr ecipi tate is formed, then th e solution tested is iron(III) chlo ride.

If no change occ urs, then the solutio n tested is iron(II) chlo ride.

Or

Potassium hexacyano ferrate(III) solut ion is pou red into 2 cm3of the solu t ion to be tested in a

test tub e.

If a greenish-brow n solutio n is formed, then the solu tion tested is iron(III) chlo ride.


Or

Now let see some questions about salt.

Tr y to solve it by yoursel f f ir st and then

compare wi th the answers provided.


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Potassium th iocyanate solu t ion is poured into 2 cm3of th e solu t ion to be tested in a test tub e.

If a bloo d red colou ration is form ed, then the solution tested is iron (III) chlo ride.


(e) sodium chloride and sodium sulphate

Si lver n i t ra te solu t ion is poured into 2 cm3

of th e solu t ion to be tested in a test tu be.I f a whi te precip i tate is form ed, then the s olu t ion tested is sodium chlor ide.

I f no change occu rs, then the solu t ion tested is sodium sulphate.

Or

Bar ium chlor ide solu t ion is poured into 2 cm3of th e solu t ion to be tested in a test tube.

I f a whi te precip i tate is form ed, then the s olu t ion tested is sodium sulphate.

I f no change occurs, then the solu t ion tested is sodium chlor ide.

Example 2:

1. State three examples ofa) soluble salts b) insoluble salts

Potassium carbonate Magnesium carbonate

Lead(II) nit rate Lead(II) su lph ate

Amm onium chlor ide Argentum chlor ide

2. Which of the following salts is soluble

3. Identify the gas that turns moist red litmus paper blue

Amm on ia gas

4. Gas X has the following properties

Gas X is carbon diox ide gas

Lead(II) chloride Sodium carbonate

Calcium sulphate Barium sulphate

Colourless

Acidic gas

Turns lime water milky


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5. Heat +

Colour of metal oxide X is yellow when hot and white when cold. Gas Y turns lime water milky.

a) Name gas Y : carbon diox ide gas

b) Name metal oxide X : zinc oxide

c) Name salt P : zinc carbonate

d) Write an equation to represent the action of heat on salt P

ZnCO3 (s) ZnO (s) + CO2(g)

6.A sample of copper(II) nitrate, Cu(NO3)2was heated strongly. Write down the expected observation.

Copper(I I) n i t rate decompos e to produc e black colour o f res idue when hot and cold. A b rown

gas that changed moist b lue l i tmus p aper to red and co lour less gas that l ighted up a glow ing

wooden s pl in ter are produced.

Salt P Metal oxide X Gas Y


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D. Numerical problem involving stoichiometric reaction in the

preparation of salt

Example 1;

Ammonium phosphate, (NH4)3PO4is use as a fertilizer. 29.8g of this salt is prepared by neutralizing

phosphoric acid, H3PO4 with ammonium gas, NH3. Calculate the volume of ammonium gas, NH3

reacted at room conditions.( Relative atomic mass; H, 1: N, 14: P, 31; O, 16; Molar volume; 24 dm3 mol-1at room conditions)

Solutions;

a. Calculate the number of moles

2.88 g

[3(14) + 12(1) + 31 + 4(16)

= 0.2 mol

b. Write a balanced chemical equation

Compare the mole ratio of NH3and(NH4)3PO4

H3PO4(aq) + 3NH3(aq) (NH4)3PO4(aq)

c. Calculate the number of moles of NH3base onthe mole ratio

= 3 X 0.2 mol

= 0.6 mol

d. Calculate the volume of NH3

Volume = number of mole X volume

= 0.6 mol X 24 dm3mol

-1

= 14.4 dm3

A balanced chemical equation for a reaction in preparation of a salt

can be used to calculate the stoichiometric quantities of the following Masses of reactants Volumes and concentrations of reactants Masses of products Volumes of products

=

3 mol 1 mol


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Example 2:3.9 g of potassium is burnt completely in the air as shown in the following equation;

4K(s) + O2(g) 2K2O(s)

What is the mass of potassium oxide produced?

[Relative atomic mass: K, 39; O, 16]

Solutions

Tip: Solve the question step by step

Step 1: Write Chemical Equation

4K(s) + O2(g) 2K2O(s)

4 mol of K react with 1 mol of O2produce 2 mol K2O

Step 2:Calculate the number of mole

[Get the information from the question]

Step 3: Find the coefficient From Balance Chemical Equation

FBCE;

4 mol of K produce 2 mol K2OThus;

0.1 mol of K produce 2/4 mol K2O = 0.2 mol K2O

FBCE;

[Sebelah kiri] [Sebelah kanan]Bil. mol yang telah dikira Bil. Mol yang hendak ditentukan

4 mol K = 2 mol K2O

0.1mol K = 2/4 x 0.1mol K2O = 0.05 mol K2O

No. of mol of K2O = 0.05 mol

Step 4: Solve the questions

Thus;Mass of K2O = 0.05 mol Molar mass

= 0.05 mol 55 g mol-1

= 2.75 g

No. of mol K =mass

Molar mass

=3.9 g

39 gmol-

0.1 mol=


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Example 3:

Acids reacts with calcium carbonate, CaCO3in limestone to form a salt and carbon dioxide, CO2.

A piece of limestone reacted completely with 100 cm3of 31.5 g dm

-3nitric acid, HNO3.

[Relative atomic mass: H, 1; C, 12; N, 14; O, 16; Ca, 40. Molar volume: 24 dm3mol

-1at room

conditions]a. Calculate the mass of salt produced.

b. What is the volume of carbon dioxide, CO2liberated at room conditions?

Step 1: Write Chemical EquationChemical Equation: 2HNO3 + CaCO3 Ca(NO3)2+ CO2 + H2O

Step 2:Calculate the number of mole

Get the information from the question;

FBCE;2HNO3 + CaCO3 Ca(NO3)2+ CO2 + H2O

2 mol HNO3 = 1 mol Ca(NO3)2

0.05 mol HNO3 = x 0.05 mol Ca(NO3)2 = 0.025 mol Ca(NO3)2

No. of mol of Ca(NO3)2= 0.025 mol

Mass of Ca(NO3)2 = 0.025 mol 40 + 2[14 + 3(16)] g mol-1

= 4.1 g

No. of mole of HNO3 =Molarity Volume

1000

=0.5 mol dm

- 100 cm

1000

= 0.05 mol

Concentration of HNO3 = 31.5 g dm-

=Molar mass of HNO3

31.5 g dm-3

= 0.5 mol dm-3

=31.5 g dm

-

1 + 14 + 48 g mol-

Change the

concentration

given in g dm-3

to mol dm

-3

first


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FBCE;2HNO3 + CaCO3 Ca(NO3)2+ CO2 + H2O

2 mol HNO3 = 1 mol CO2

0.05 mol HNO3 = x 0.05 mol CO2 = 0.025 mol CO2

No. of mol of CO2 = 0.025 mol

Volume of CO2 = 0.025 mol 12 + 2(16) dm3mol

-1

= 1.1 dm3

Example 4:

Pb(NO3)2compound decomposes when heated as shown in the following equation.

If 6.62 g of Pb(NO3)2compound is heated, calculate;

[Relative atomic mass: N, 14; O, 16; Pb, 207; 1 mol of gas occupies 22.4 dm3at s.t.p.]

(i) mass of PbO that is produced

(ii) volume of nitrogen dioxide produced at s.t.p(ii) volume of oxygen produced at s.t.p

Solution:

FBCE; 2Pb(NO3)2 2PbO + 4NO2 + O2

2 mol Pb(NO3)2 = 2 mol PbO

0.02 mol Pb(NO3)2 = 0.02 mol PbO

No of mol PbO = 0.02 mol

Mass of PbO = 0.02 x 223 = 4.46 g

No of mol Pb(NO3)2 =mass

Molar mass

=6.62 g

331 gmol-

0.02 mol=

2Pb(NO3)2 2PbO + 4NO2 + O2


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2 mol Pb(NO3)2 = 4 mol NO2

0.02 mol Pb(NO3)2 = 4/2 x 0.02 mol O2 = 0.04 mol O2

No of mol O2= 0.04 mol

Volume of O2= 0.04 x 22.4 dm3

= 0.896 dm3 // 896 cm

3


2 mol Pb(NO3)2 = 1 mol O2

0.02 mol Pb(NO3)2 = x 0.02 mol O2 = 0.01 mol O2

No of mol O2= 0.01 mol

Volume of O2= 0.01 x 22.4 dm3

= 0.224 dm3 // 224 cm

3

Numerical Problems involving stoichiometric reactions in the precipitation of salts

Question 1:

A student prepare copper(II) nitrate, Cu(NO3)2by reacting copper(II) oxide, CuO with 200 cm3of 2.0

moldm

-3

nitric acid, HNO3. Calculate the mass of copper(II) oxide, CuO needed to react completelywith the acid.

[Relative atomic mass: Cu, 64 ; O, 16]

Question 2:

X cm3of 0.5 moldm

-3sulphuric acid, H2SO4is added to 100 cm

3of 1.0 moldm

-3lead(II) nitrate

solution to produce lead(II) sulphate, PbSO4.[Relative atomic mass: Pb, 20; O, 16; S, 32]

a. Calculate the value of X.b. Calculate the mass of lead(II) sulphate obtained.

Star t to do exercises from any book.

I wil l help and guide you to master this topic.

Prepared by;Kamal Ariffin Bin SaaimSMKDBL

Notes Salts (Chemistry)

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