Chapter 8: Salts

A. Salts

- Usage of salts in daily lives:

Application ExampleAgriculture 1. Acidic soil is treated with powdered _____________________ (calcium oxide, CaO),

_______________ (calcium carbonate, CaCO3) or ashes of burnt wood.

2. Basic soil is treated with compost. The _____________ gas from the decomposition of

compost __________________ the alkalis in basic soil.

3. The acidity of water in farming is controlled by adding _______________ (calcium oxide,

CaO).

Industries 1. Acidic gases emitted by industries are neutralized with ________________ (calcium oxide,

CaO) before the gases are released into the air.

2. Organic acid produced by bacteria in latex is neutralized by __________________________

and prevents coagulation.

Health 1. Excess acid in the stomach is neutralized with its anti-acids that contain bases such as

_____________________, ______________________ and ______________________.

2. Toothpastes contain ___________________ (such as magnesium hydroxide) to neutralize

the acid produced by bacteria in the mouth.

3. ____________________________ is used to cure acidic bee stings

4. ________________ (ethanoic acid) is used to cure alkaline wasp sting.

- Definition of salt: A salt is a compound forms when the ______________ ion, H+ from an ____________ is

replaced by a _______________ ion or an ammonium ion, NH4+.

- The chemical formula of a salt comprises a ____________ (other than hydrogen ion) and an anion (other

than ____________ ion and _____________ ion).

- Two types of salts: Soluble Salts and Insoluble Salts

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- Solubility of Salts

Salt Solubility in waterSodium, potassium and ammonium salts (Na+, K+, NH4

+) All are soluble

Nitrate salt (NO3-)

All are soluble

Chloride salt (Cl -) All chloride salts are soluble in water except PbCl2, AgCl

and HgCl2

Sulphate salt (SO42-)

All sulphate salts are soluble in water except PbSO4, BaSO4 and CaSO4

Carbonate salt (CO32-)

All carbonate salts are insoluble except Na2CO3, K2CO3

and (NH4)2CO3

Exercise : Determine whether each of the following salt is soluble or insoluble in water.Salt Solubility ( , X

)1. Magnesium chloride2. Lead(II) sulphate3. Calcium carbonate4. Zinc chloride5. Silver chloride6. Potassium carbonate7. Lead(II) nitrate8. Sodium sulphate9. Ammonium chloride10. Barium sulphate

Formula of Salt Solubility ( , X )1. CaCO3

2. ZnCl2

3. Na2SO4

4. AlCl3

5. K2CO3

6. AgCl7. BaSO4

8. (NH4)2CO3

9. CaSO4

10. PbCl2

Preparations of Salts

- Preparation of salts depends on the _______________ of the salt.

Preparing soluble salts of ammonium, sodium and potassium

- Ammonium salts, sodium salts and potassium salts can be prepared by ______________________ reaction

between acids and alkalis.

- Ammonium salts are obtained by neutralizing ___________________ solution using dilute acid.

- Sodium salts are prepared by neutralizing ______________________________ solution with dilute acids.

- Potassium salts are prepared by neutralizing ____________________________ solution with dilute acids.

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Soluble salt Sodium Chloride, NaCl

Name two chemical substances to prepare the salt 1. …………..…………………………..

2. ………………………………………

Chemical equation

Procedure: (Diagram) Description

Preparing soluble salts other than Ammonium, Sodium and Potassium

- Soluble salts other than ammonium, sodium and potassium can be prepared by one of the following reactions: Reaction between an acid and a ______________________. Reaction between an acid and a _____________________________________. Reaction between an acid and a metal _________________.

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Soluble salt Copper(II) sulphate, CuSO4

Name two chemical substances to prepare the salt 1. …………..…………………………..

2. ………………………………………

Chemical equation

Procedure: (Diagram) Description

- Special remarks for reaction between dilute acids and metals:

Avoid using nitric acid because it will give a complicated mixture of products.

Unreactive metals such as ______________ and ______________ do not react with dilute acids so we

should use oxides, hydroxides or carbonates of copper and silver.

Do not react acids with very reactive metals such as ______________ and __________________

because it will cause explosions.

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- Physical Characteristics of Crystals

Crystals have _______________ geometrical shapers. Crystals of the same substances have ____________ shapes but may be in _________________ sizes. Crystals have _____________ surfaces, straight edges and ___________________ angles. Crystals have _______________ angles between two neighbouring surfaces.

Preparation on Insoluble Salts

- An insoluble salt is prepared through ______________________________ method through a

____________________________ reaction.

- In this method, ____________ aqueous solutions of two different soluble salts are mixed together to form the

insoluble salt. The insoluble salt is the ________________________ and can be obtained by

___________________________.

- The first solution must have a soluble salt which contains the _______________ of the insoluble salt while

the second solution must have a soluble salt which contains the ________________ of the insoluble salt.

- Easier ways to choose the aqueous solutions

Choose a nitrate salt to provide the required cation. (Because all nitrate salts are soluble in water.)

Choose a sodium or potassium salt to provide the required anion. (Because all sodium and potassium

salts are soluble in water.)

Soluble salt Lead(II) iodide, PbI2

Name two chemical substances to prepare the salt 1. …………..…………………………..

2. ………………………………………

Chemical equation

Ionic equation

Procedure: (Diagram) Description

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Guidelines for Preparation of a Specified Salt

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B. Qualitative Analysis of Salts

1. Qualitative analysis of salt is a chemical technique used to determine what are the cations and anions present in the salt.

2. General procedures involved in qualitative analysis of salts:

3. Tests for cations can be done using two reagents: sodium hydroxide solution and ammonia solution.(Refer to the flow chart for qualitative analysis of cations)

Experiment 1: Confirmatory Tests for some specific cations

Part A: Confirmatory test for ammonium ion, NH4+

1. Pour 2 cm3 of ammonium chloride, NH4Cl solution into a test tube.

2. Add a few drops of Nessler’s reagent to the test tube using a dropper. Shake well.

3. Record your observation.

Part B: Confirmatory test for iron(II) ion

1. Pour 2 cm3 of iron(II) sulphate solution into a test tube.

2. Using a dropper, add a few drops of sodium hydroxide solution, NaOH into the test tube and shake well.

3. Record your observation.

Part C: Confirmatory test for lead(II) ion

1. Pour 2 cm3 of lead(II) nitrate, Pb(NO3)2 solution into a test tube.

2. Using a dropper, add 2 cm3 of potassium iodide, KI solution into the test tube and shake well.

3. Observe any precipitate formed and record its colour.

4. Add about 3 cm3 of distilled water and boil the mixture.

5. Cool the contents using running water from the tap.

6. Record your observations.

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Observations on the physical properties of salts

Action of heat on salts

Test for cations and anions

Confirmatory tests for cations and anion

Observations:Experiment Observations

Part A

Part B

Part C

Experiment 2: Action of Heat on Carbonate and Nitrate Salts

Part A: Action of Heat on Carbonate Salts

1. About two spatulaful of zinc carbonate are placed in a test tube.

2. The colour of the carbonate salt is noted.

3. The test tube is stoppered with a delivery tube dipping into lime water.

4. The carbonate salt is then heated strongly.

5. Any changes that occur to the lime water and also the colour of the residue when it is hot and when it is cold

are recorded.

Part B: Action of Heat on Nitrate Salts

1. About two spatalaful of lead(II) nitrate are placed in a test tube.

2. The colour of the nitrate salt is noted.

3. The nitrate salt is then heated strongly.

4. The gas liberated are tested by

(a) lowering a glowing wooden splinter into the test tube.

(b) bringing a piece of moist blue litmus paper to the mouth of the test tube.

5. The colour of the residue when it is hot and when it is cold are recorded.

Observations:

Experiment Observations

Part A

Part B

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Experiment 3: Tests for Anions

Part A: Test for chloride ions, Cl -

1. Pour 2 cm3 of 1 moldm-3 ammonium chloride, NH4Cl solution into a test tube.

2. Add dilute nitric acid, HNO3 into the test tube until no further change occurs.

3. Then, add 2 cm3 of 1 moldm-3 silver nitrate, AgNO3 solution.

4. Record your observation.

Part B: Test for sulphate ions, SO42-

1. Pour 2 cm3 of 1 moldm-3 iron(II) sulphate, FeSO4 solution into a test tube.

2. Add dilute hydrochloric acid, HCl into the test tube slowly until no further change occurs.

3. Then, add 2 cm3 of 1 moldm-3 barium chloride, BaCl2 solution.

4. Record your observation.

Part C: Test for nitrate ions, NO3-

1. Pour 2 cm3 of 1 moldm-3 lead(II) nitrate, Pb(NO3)2 solution into a test tube.

2. Add 2 cm3 of dilute sulphuric acid, H2SO4 follow by 2 cm3 of iron(II) sulphate, FeSO4 solution into the test

tube and shake well.

3. Hold the test tube in a slanting position and add 1 cm3 of concentrated sulphuric acid, H2SO4 along the side of

the test tube using a dropper. Do not shake the test tube.

4. Record your observation.

Observations:

Experiment Observations

Part A

Part B

Part C

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Cations Analysis Flow Chart

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Anions Analysis Flow Chart

*ppt : precipitate

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