Chemistry, C8A_aaNotes(S)

8/8/2019 Chemistry, C8A_aaNotes(S)

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Chapter 8 : SALTS

A Synthesizing Salts

1. Meaningof salts

Example 1 :

HCl H

+

+ Cl

-

HNO3 H+ + NO3

-

Example 2 :

Na+ NaCl

NH4

+NH

4NO

3

H+ SO42-

Sulphuric acid

Cu2+ SO42-

CuSO4

K+ SO4

2-

K2SO

4

NH4

+ SO4

2-

(NH4)

2SO

4

Zn2+ SO4

2-

ZnSO4

Al3+ SO4

2-

Al2(SO

4)

3

Na+ SO4

2-

Na2SO4

Salt is an ionic compound formed when the.ion,

from an acid is replace by a metal ion oran ammonium ion.


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4541 CHEMISTRY Chapter 8

Activity 1:-

1 Complete the diagram below :

Chapter 8 Salts

2

H+ ..

Hydrochloric acid

Cu2+

K+

NH4

+

Zn2+

Al3+

Na+

H+ ..

Nitric acid

Cu2+

K+

NH4

+

Zn2+

Al3+

Na+

DIAGRAM 1.1


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2 Write down the chemical formula of salts :

2. Uses Of Salts In Our Daily Lives

USES OF SALTS

Agriculture Medicinal Field Food Industries Chemical Industries

Chapter 8 Salts

Metal ionSulphate salt Chloride salt Nitrate salt Carbonate salt

(H2SO4) (HCl) (HNO3) (H2CO3)

Na+

K+

Mg2+

Ca2+

Al3+

Zn2+

Fe2+

Pb2+

Cu2+

Ag+

Ba2+

NH4+

3

DIAGRAM 1.2


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Type of salt3. Soluble andInsoluble Salt

Types of salts :

Soluble salt salts that can be dissolve in water at room temperature.

Insoluble salt salts cannot be dissolve in water at room temperature.

Solubility of salt in water

All sodium (Na+), potassium (K+) and ammonium (NH4+) salts are soluble. All nitrate salts are soluble.

All sulphate salts are soluble except PbSO4 , CaSO4 and BaSO4 All chloride salts are soluble except PbCl2 and AgCl, HgCl All carbonate salts are insoluble except K2CO3, Na2CO3 and (NH4)2CO3.

Attention!All metal oxides and hydroxides are insoluble in waterexcept Na2O, K2O, NaOH and KOH.(Barium hydroxide and calcium hydroxide areslightly soluble in water)

Activity 2:-

*Shade the insoluble salts inActivity 1; Question 2.

Activity 3:-

Classify the salt in the table below :

Type of salt Soluble Insoluble

Nitrate

Chloride

Sulphate

Carbonate

Sodium carbonate, Na2CO3

Potassium carbonate, K2CO3

Ammonium carbonate, (NH3)2CO3

All other carbonate salts

Chapter 8 Salts

4

EXCEPT

EXCEPT


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4. The PREPARATION of salt depends on itssolubility in water.

.

Chapter 8 Salts

5

Preparation of salt

Soluble Insoluble

K+, Na+, NH4

+ Other than K+, Na+,NH

4

+ salt

Titration of acid and alkali

method using an indicator.

Acid + metal Salt + H2Acid + metal oxide/base Salt + H

2O

Acid + metal carbonate Salt + H2O + CO

2

Mix twosolutions containing cations

and anions of insoluble salts.

Stir with glass rod.

Filter using filter funnel.Rinse the residue with distilled water.

Dry the residue with filter paper.

Add acid to the alkali until it is

neutral with the aid of anindicator.

Repeat the procedure without

using an indicator.

Evaporate the filtrated until it becomes asaturated solution.

Dip in a glass rod, if crystals are formed

immediately, the solution is saturated.

Cooled at room temperatureFilter and dry by using filter paper.

Method I Method II

Acid + Alkali Salt + H2O

Add metal/base oxide fillings/excessive

metal carbonate to the acid and heat it.

Filter to remove excess solid (residue).

Method III

Double decomposition reaction[Method : Precipitation]


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Activity 4 :-

Based on your practical book[ page 113] and diagrams given, describe how to prepare the

potassium chloride salts in the laboratory. (Method I)

1. 25.0 cm3 of 1 mol dm-3 . solution is measured using 25.0

cm3 pipette and transferred into a conical flask.

2. 2 or 3 drops of . are added into the conical flask. [the

colourless solution turns pink]

3. A clean burette is filled with 1 mol dm-3 of . The initial

reading of the burette is recorded.

4. . from the burette is added slowly into the

. solution while shaking the conical flask, until the pink

solution turns ..

5. The final reading of the burette is recorded.

6. Volume of hydrochloric acid added to the sodium hydroxide solution is calculated and

recorded.

7. Step 1 to 5 are repeated without the using phenolphthalein, using the volume of hydrochloric

acid obtained

Chapter 8 Salts

6

V cm3

KOH

KOH

KOH

Salt solutio

(no indicato


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8. The salt solution in the conical flask is poured into an evaporating dish.

9. The solution is heated until it becomes .

10. The hot saturated solution is . to room temperature for

crystallisation to occur.

11. The contents are . to obtain the potassium chloride, KCl

crystals.

12. The crystals are pressed between two pieces of filter paper to be dried.

13. The chemical equation : NaOH + HCl ___________ + H2O

Activity 5 :-

1 Diagram below shows the method of preparing a soluble salt.Complete the diagram by drawing the set-up of apparatus used to obtain the salt crystals in the

space provided.

Chapter 8 Salts

7

Salt solution

The solution is allowed to cool

50 cm3 of 2.0 mol dm-3

acid

Metal oxide powder

Salt solution

Heat

Excess metal oxide

Dry salt crystals are obtained

Filter papers


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(a) State two steps that are required to speed up the reaction betwen metal oxide and acid.

........................................................................................................................................

........................................................................................................................................

(b) Based on the diagram, state two substances that are used to prepare zinc chloride salt.

........................................................................................................................................

2 Diagram below shows the method of preparing an insoluble salt.

(a) Based on the diagram, state two suitable substances that are used to prepare lead(II)iodide salt.

........................................................................................................................................

(b) State the type of reaction in (a).

........................................................................................................................................

(c) Write the ionic equation for the reaction.

........................................................................................................................................

Chapter 8 Salts

8

Solution X

Salt

DryMixing two solution

Solution Y

Filter and rinse

Salt


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3 Complete the table below with the suitable substances :

Solution X Solution Y Salt Z

Sodium sulphate Lead(II) sulphate

Calcium chloride Potassium Calcium sulphate

Barium sulphate

Silver chloride

Lead(II) chloride

Zinc carbonate

Calcium carbonate

5. PURIFICATION of soluble salts :

Soluble saltpurifiedthrough .. process.

Diagram :

Chapter 8 Salts

9

Salt solution

The solution is allowed to cool

Distilled water

Impure salt

Salt solution

Heat

Impurities

Dry pure salt crystals

Stir


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Activity 5 :-

Write for soluble salts and X for insoluble salts.Write allthepossible chemical equations to prepare the soluble saltsWrite chemical equation and ionic equation for insoluble salts.

Salt / X Equation

Zinc chloride

Zn + HCl

ZnO + HCl

ZnCO3 + HCl

Sodium nitrate

Silver chloride X

Copper(II) sulphate

Lead(II) sulphate

Aluminium nitrate

Lead(II) chloride

Magnesium nitrate

Potassium chloride

Chapter 8 Salts

10


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Lead(II) nitrate

Barium sulphate

Activity 6 :-

1 Salt is prepared by following methods :

Method A : reaction between metal oxide and acid. Method B : double decomposition involving two solutions of salts.

You are required to prepare lead(II) sulphate and copper(II) sulphate salts.(a) Based on the method above, select suitable method to prepare each salt.

(b) State the chemical substances needed for preparing each salt.

(c) Write a chemical equation to prepare each salt.(d) Describe an experiment to prepare each salt.

2 (a) The following are three examples of chloride salts that can be prepared in the laboratory.

Sodium chloride

Lead(II) chloride

Copper(II) chloride

(i) From these examples, identify the soluble salt and insoluble salt.

(ii) State the reactants for the preparation of the insoluble salt in (a) (i).

(b) You are required to prepare magnesium nitrate salt from the chemical substances provided

below.

Your answer should include the chemical equations involved in the reactions.

3

Describe a laboratory experiment to prepare a dry magnesium sulphate.

In your description, include the chemical equation involved.

Chapter 8 Salts

11

Magnesium sulphate is a soluble salt

Magnesium oxide

Dilute nitric acid


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4 Diagram below shows the reactions involved in the preparation of soluble salts.

(a) Sodium, potassium and ammonium salts can be prepared using reaction between acid

and alkali. State the reactionX, YandZ.

(b) By choosing one of the reactions in (a) (i), suggest example of reactants used andproducts formed.

Write the chemical equation for the reaction based on your suggestion.

5 Diagram below shows a series of reactions for the production of copper(II) nitrate andsubstance B with coper(II) carbonate as the initial reactant.

(a) State the name of the

Chapter 8 Salts

12

Soluble salts

Potassium salts

Ammonium salts

Sodium salts

Other salts

Asid + alkali salt + water

ReactionX

Reaction Y

ReactionZ

CuCO3

Solution A+

CO2

+

Water

Cu(NO3)2+

Substance B

+ HCl

Stage I

+ Pb(NO3)

2

Stage II


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(i) Solution A :

..

(ii) Substance B :

..

(b) In Stage I, 20 cm3 of 1.0 mol dm-3 hydrochloric acid is reacted with excess copper(II)

carbonate powder.

(i) Write the chemical equation for this reaction.

..

(ii) Calculate the maximum volume of carbon dioxide gas that can be produced at room

condition.

[The molar volume of any gas is 24 dm3

mol-1

at room condition]

(c) (i) Name the type of reaction that takes place in Stage II.

..

(ii) State how to separate substance B from the mixture.

..

6 Diagram below shows the set up of apparatus for the preparation of copper(II) sulphate.Copper (II) oxide powder is added into acid X until in excess.

Chapter 8 Salts

13

Excess copper(II) oxide

powder

Acid X

xxxxxxxxxxxxxx

Heat

Stir


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(a) State the colour of copper(II) sulphate solution.

...................................................................................................................................

(b) Based on the diagram, state the name the of acid X used to prepare copper(II) sulphate.

...............

(c) Write the chemical equation for the preparation of copper (II) sulphate.

...................................................................................................................................

(d) State the reason why copper(II) oxide powder is added until in excess.

...............

7 Which of the following salts can be prepared by a precipitation method?

A Sodium sulphate

B Copper(II) chloride

C Lead(II) chloride

D Potassium carbonate

8 Which of the following reactions does not produce magnesium chloride?

A Magnesium oxide and hydrochloric acid

B Magnesium powder and hydrochloric acid

C Magnesium nitrate and hydrochloric acid

D Magnesium carbonate and hydrochloric acid

9 A white precipitate formed when sodium sulphate solution is added to solution Z.Which of the following solutions is most probably solution Z?

Chapter 8 Salts

14


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A Zinc nitrate

B Silver nitrate

C Calcium nitrate

D Magnesium nitrate

B Qualitative Analysis of Salt

Identification of ions[Qualitative Analysis]

The qualitative analysis involves three important steps :I Physical properties

II Thermal effect

III Confirmatory tests for cations and anions

I Physical Properties

(a) Physical state at room conditions :

Most of salts exist as solidionic compound If the salt exist as an aqueous solution it must be asoluble salt.

(b) Colour

SolidAqueoussolution

Salts / Metal oxide

White Colourless K+, Na+, Ca2+, Mg2+, Al3+, Zn2+, Pb2+, NH4+ salt

Green CuCO3

Light Green Light Green Fe2+ saltFeSO4, FeCl2, Fe(NO3)2

Blue Blue CuSO4, Cu(NO3)2,CuCl2

Brown Brown Fe3+ saltFe2(SO4)3FeCl3, Fe(NO3)3

Black CuO

Yellow when hotZnO

White when cold

Brown when hotPbO

Yellow when cold

Chapter 8 Salts

15


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II Thermal Effect

Test For Gases

PROCEDURE / TEST OBSERVATION INFERENCELower aglowingwooden splinterinto thetest tube.

Glowing wooden splinter is

rekindled.

The gas liberated is

oxygen, O2

Bring a lightedwooden splinterto themouth of the test tube.

A colourless gas thatexplodes with a popsound.


hydrogen, H2

Bubble/flow the gas produced into lime

water.

Lime water turns

milky/chalky // White

precipitate is formed.


carbon dioxide, CO2

Bring a piece of moist red litmus paper tothe mouth of the test tube. Moist red litmus paperturns blue.


alkaline,it is ammonia, NH3

Bubble the gas produced through acidified

potassium manganate(VII) solution.

Purple colour of theacidifiedKMnO4 solution

is decolourises.


sulphur dioxide, SO2

Chapter 8 Salts

Gas Test / Observation Anion

Nitrogen dioxide NO2 Brown gas/fumes is liberated.

NO3-

Oxygen O2Colourless gas, rekindles

glowing wooden splinter

Carbon dioxide CO2 Lime water turns chalky CO32 -

16

SaltMetal oxide

(residue identification refers

to specific cation only)

Gas(gas identification refers to

specific anion only)

+


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Bring a piece of moist blue litmus paper tothe mouth of the test tube.

A brown gas is liberatedMoist blue litmus paperturns red.


nitrogen dioxide, NO2

Bring a piece of moist blue litmus paper to

the mouth of the test tube.

A greenish-yellow gas isliberated.

Moist blue litmus paperturns red.


acidic,

it is chlorine, Cl2

Bring a piece of moist blue litmus paper tothe mouth of the test tube.

Moist blue litmus paperturns red.


acidic and it is

hydrogen chloride,HCl

1. Thermal effect on nitrate and carbonate salts.

Activity 6 :-

Write down the chemical equations for the reactions that occur.

Cation Nitrate (NO3- ) Carbonate (CO32 -)

(i) Decompose into metal nitrite and O2 gas Is not decomposed by heat

K+ ..KNO3 KNO2 + O2

Na+

(ii) Decompose into metal oxide, NO2 gas and O2 gas Decompose into metal oxide and CO2 gas

Ca2+ CaCO3 CaO + CO2

Mg2+

Al3+

Zn2+

Fe3+

Chapter 8 Salts

17

Nitrate salt Metal oxide NO2

+ O2

+

Carbonate salt Metal oxide CO2+

Except:

Potassium,sodium and

ammoniumsalt.


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Pb2+

Cu2+ Cu(NO3)2 CuO + NO2 + O2

Sulphate salts usually do not decompose. Chloride salts do not decompose except NH4Cl.

NH4Cl(s) NH3(g) + HCl(g) [sublimation process ]Activity 7 :-

1 Table below shows the incomplete observation for an experiment :

Experiment Procedure Observation

Copper(II) carbonate is heatedand the gas produced is passed

through lime water.

1. Green solid turns

2. The lime water turns

(a) Complete the observation on the table above.

(b) Based on the observation, name the products in the experiment and write the chemicalequation for the reaction occured.

Products : ..

Chemical equation :

2 Diagram below shows the decomposition of compound X to form lead(II) oxide, and gas Q.

Gas Y is a brown gas.

Based on the diagram above,

(i) state the name of the gas Y.

................................................................................................................................................

(ii) state the colour of lead(II) oxide when it is hot and cold.

Chapter 8 Salts

18

Heat

Compound X Lead(II) oxide Gas Y+ Gas Z+


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................................................................................................................................................

(iii) write the formula of compound X.

................................................................................................................................................

(iv) write the chemical equation for the reaction.

................................................................................................................................................

2. Confirmatory Tests for Cations and Anions

(a) Chemical tests should be conducted for the confirmation of anions and cations in aqueous

form.

(b) Cation confirmation It is done by adding a small amount of sodium hydroxide solution,NaOH(aq) / aqueous ammonia solution, NH3(aq) followed by excess sodium hydroxide /aqueous ammonia solution.

(i) Reaction with sodium hydroxide solution, NaOH(aq)

Chapter 8 Salts

19

Cation

+ NaOH(aq)

Precipitateformed?No

Yes

Colour ofprecipitate

White

+ excess NaOH(aq)

Blue

Cu2+

Green

Fe2+

Brown

Fe3+Precipitate

dissolve?

No Yes

NH4

+

Mg

2+

Ca

2+

Pb2+Al3+Zn2+

Sodium hydroxide

Solution with cation


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(ii) Reaction with ammonia solution, NH3(aq)

Chapter 8 Salts

20

Cation

+ NH3(aq)

Precipitateformed?

No Yes

Colour ofprecipitate

White

+ excess NH3(aq)

Blue

Cu2+

Green

Fe2+

Brown

Fe3+Precipitate

dissolve?

No Yes

NH4+

Pb2+Al3+Mg2+

Ammonia solution

Solution with cation

Zn2+

Ca2+

+ excess NH3(aq)

Precipitate dissolve

in excess NH3(aq)

to form blue

solution


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3. Confirmatory Tests For Cations

CationsTest with a small amount of sodiumhydroxide solution until in excess

Test with a small amount of ammoniasolution until in excess

Ca2+ white precipitate, insoluble in excess -

Mg2+ white precipitate, insoluble in excess white precipitate, insoluble in excess

Al3+ white precipitate, soluble in excess white precipitate, insoluble in excess

Zn2+ white precipitate, soluble in excess white precipitate, soluble in excess

Fe2+green precipitate, insoluble in excess green precipitate, insoluble in excess

Fe3+ brown precipitate, insoluble in excess brown precipitate, insoluble in excess

Pb2+ white precipitate, soluble in excess white precipitate, insoluble in excess

Cu2+ blue precipitate, insoluble in excess blue precipitate, soluble in excess

NH4+

- -

Confirmatory Tests for ammonium ion, NH4+

(a)Nessler reagent

a small amount ofNessler reagent is added into the solution. brown precipitate are formed.

Chapter 8 Salts

21


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(b) Heat sodium hydroxide solution is added to a small amount of solution contains NH4

+

the solution is heated. A piece of moist red litmus paper is placed. Red moist litmus paper turns blue.

4. To differentiate between Al3+ and Pb2+

Write the ionic equations for the formation of precipitate :

(a) : .

(b) : .

(c) : .

Chapter 8 Salts

22

Al3+ // Pb2+

+ H2SO

4/ Na

2SO

4

No changes

Al3+

Whiteprecipitate

Pb2+

+ HCl / NaCl

No changes

Al3+

Whiteprecipitate

Pb2+

+ KI

No changes

Al3+

Yellowprecipitate

Pb2+(a) (b)

(c)

heat

NH4+

+NaOH(aq)


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5. Confirmatory Tests ForAnions

Anion Tests Conclusion / Ionic equation

CO32-2 cm

3

of dilute HCl / H2SO4 is added to 2 cm3

ofaqueous solution of carbonate ions.Effervescence occurs and the gas released turnslime water chalky.

Cl-Dilute HNO3 is added to 2 cm3 of an aqueous

solution of chloride ions followed by

2 cm3 ofsilver nitrate solution.A whiteprecipitate is formed.

SO42-Dilute HCl / HNO3 is added to 2 cm3 of an aqueoussolution of sulphate ions followed by 2 cm3 bariumchloride / barium nitrate solution.A whiteprecipitate is formed.

NO3-

2 cm3 of dilute H2SO4 is added to solution of nitrateions followed by 2 cm3 ofIron(II) sulphate. Themixture is shaken. The test tube is slanted and held

with a test tube holder. A few drops ofconcentratedH2SO4 acid is dropped along the wall of the test tubeand is held upright.

A brown ring is formed.

-

Chapter 8 Salts

23


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Activity 8 :-

1 Table below shows four types of salts.

With reference to the salts given above, answer the following question :

(a) Write the chemical formula of sodium carbonate.

..................................................................................................................................

(b) Name the salt which is insoluble in water.

..................................................................................................................................

(c) (i) What is observed when zinc nitrate salt is heated.

..............................................................................................................................

(ii) Write the chemical equation to represent the reaction.

.....................................................................................................................

(d) State the type of reaction in the preparation of lead(II) chloride salt.

........................................................................................................................................

(e) Describe how to verify copper(II) ion and sulphate ion in copper(II) sulphate solution.

(i) copper(II) ion :

..............................................................................................................................

..............................................................................................................................

Chapter 8 Salts

24

Sodium carbonate

Zinc nitrateLead(II) chloride

Copper(II) sulphate


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(ii) sulphate ion :

..............................................................................................................................

..............................................................................................................................

2 Nitric acid reacts with substance Y and produces a gas which changes lime water chalky as oneof the products.

Which of the following is substance Y?

A Mg

B NaOH

C CaCO3D Al2O3

3 When potassium hexacyanoferrate(II) solution is added to solution X, a dark blue precipitate isformed. Then, solution X is added with barium chloride solution in another test tube, a white

precipitate is formed. The formula of the solution X is ..

A FeCl2B FeSO4

C Fe(NO3)3D Fe2(SO4)3

4 Which of the following reagent can be used to differentiate iron(II) ion, Fe2+ and iron(III) ion, Fe3+?

I Ammonia solutionII Potassium bromide solutionIII Acidified potassium manganate(VII) solutionIV Potassium hexacyanoferrate(II) solution

A I and II

B I and IVC II and IIID III and IV

5 A white precipitate formed when sodium sulphate solution is added to solution Z.Which of the following solutions is most probably solution Z?

Chapter 8 Salts

25


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A Zinc nitrateB Silver nitrateC Calcium nitrateD Magnesium nitrate

6 Figure below shows an incomplete flow chart of cation and anion tests for salts X?

(ii) Describe the test that you use in the laboratory to confirm that salt X contains magnesiumions, Mg2+ and nitrate ions, NO3

-. Include in your observations.

[10 marks]

26

Cation test

Salt X

Mg2+

Anion test

NO3

-

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Chemistry, C8A_aaNotes(S)