6.9 PREPARATION OF SALTS

Learning Standards
Pupils are able to :
6.9.1 Test the solubility of salts in water and classify them into
soluble and insoluble salts through experiments
6.9.2 Describe the preparation of a soluble salt through activity
6.9.3 Describe the preparation of an insoluble salt through
activity
6.9.4 Construct an ionic equation using the continous variation
method through experiment

Learning Objectives
A student is able to :
 Identify soluble and insoluble salts
 Describe the preparation of soluble salts
 Describe the purification of soluble salts by recrystallisation
 Describe the preparation of insoluble salts,
 Write chemical and ionic equations or reactions used in the
preparation of salts
 Design an activity to prepare a specified salt, construct ionic
equations through the continuous variation method
 Solve problems involving calculation of quantities of
reactants or products in stoichiometric reactions

• Soluble salt can be prepared through following reactions :
• EXPERIMENT 6.9.1 Test the solubility of salt in water and
classify them into soluble and insoluble salts through
experiment
• EXPERIMENT 6.9.2 Describe the preparation of a soluble salt
through activity
• EXPERIMENT 6.9.3 Describe the preparation of an insoluble
salt through activity
• EXPERIMENT 6.9.4 Construct an ionic equation using the
continuous variation method through experiment.

• Carry out an activity to purify a soluble salt using the
recrystallisation method.
• Prepare an insoluble salt using the double decomposition
reaction.
• Carry out an activity to construct an ionic equation for the
formation of an insoluble salt using the continuous variation
method.

EXPERIMENT 6.9.1 TO TEST THE SOLUBILITY OF SALT IN WATER AND CLASSIFY THEM
INTO SOLUBLE AND INSOLUBLE SALTS THROUGH EXPERIMENT
Aim : Investigate the solubility of various salts in water
Problem statement : Do all salts dissolve in water?
Hypothesis : Some salts dissolve in water, some salts do not.
Variables :
Manipulated : Types of nitrate, sulphate, chloride, carbonate and ammonium salt
Responding : Solubility of salt in water
Fixed : Volume and temperature of water, mass of salt

1. Based on Figure 6.36, list out the apparatus and materials/substances used in this
experiment.
2. Plan the experiment procedure with the members of your group.
3. Prepare an appropriate table to record your observation.
4. Carry out the experiment with your teacher̕
s permission.
5. Record the observation obtained in the table you have prepared.

1. Based on Figure 6.36, list out the apparatus and materials/substances used in this
experiment.
Materials : Potassium chloride, KCl, zinc chloride, ZNCl2, sodium nitrate, NaNO3,
magnesium nitrate, Mg(NO3)2, ammonium sulphate, (NH4)2SO4, barium
sulphate, BaSO4, sodum carbonate, Na2CO3, lead(II) carbonate, PbCO3 and
distilled water
Apparatus : Electronic balance, 100 cm3 measuring cylinder, spatula, 50 cm3 beaker,
glass rod

Procedures :
1. Weigh 5g of sodium chloride salt.
2. Add 20 cm3 of distilled water to the salt.
3. Stir using glass rod.
4. Observe and record the results in the table.
5. Repeat steps 1 to 4 with other salts.

Results :
Type of salt Solubility
Potassium chloride, KCl S
Zinc chloride, ZNCl2 S
Sodium nitrate, NaNO3 S
Magnesium nitrate, Mg(NO3)2 S
Ammonium sulphate, (NH4)2SO4, S
Barium sulphate, BaSO4 I
Sodium carbonate, Na2CO3 S
Lead(II) carbonate, PbCO3 I

Interpreting data:
1. Based on the results of the experiment, list out:
(a) Nitrate, sulphate, chloride, carbonate and ammonium salts that dissolve in water
(b) Sulphate, chloride and carbonate salts that do not dissolve in water
2. Formulate and classify the types of salt that dissolve or do not dissolve in water in
an appropriate table.

Interpreting data:
1. Based on the results of the experiment, list out:
(a) Nitrate, sulphate, chloride, carbonate and ammonium salts that dissolve in water
(b) Sulphate, chloride and carbonate salts that do not dissolve in water

Interpreting data:
2. Formulate and classify the types of salt that dissolve or do not dissolve in water in
an appropriate table.

Conclusion :
Is the hypothesis acceptable? What is the conclusion of this experiment?

SOLUBILITY OF SALT IN WATER
• Solubility is the ability of a compound to dissolve in a solvent.
• Some salts are soluble in water while others are not.
• The solubility of a salt in water depends on the types of cations and
anions present in the salt.
Type of salt Solubility in water
Sodium, potassium and
ammonium salts (SPA)
All are soluble
Nitrate salts All are soluble
Chloride salts All are soluble except PbCl2, AgCl and HgCl (PAH)
Sulphate salts All are soluble except PbSO4, BaSO4 and CaSO4
(PaBaSOCaSO)
Carbonate salts All are INSOLUBLE except SPA salts
(Na2CO3, K2SO3 and (NH4)2CO3)

Classify the following salts into soluble and insoluble salts in the tree map below.
Magnesium sulphate, potassium chloride, lead(II) chloride, ammonium nitrate,
calcium carbonate, lead(II) nitrate, silver chloride, calcium nitrate, barium sulphate,
calcium sulphate, sodium carbonate and copper(II) carbonate.
Salt
Soluble salt Insoluble salt
1. Potassium chloride
2. Magnesium sulphate
3. Ammonium nitrate
4. Sodium carbonate
5. Lead(II) carbonate
6. Calcium nitrate
1. Lead(II) chloride
2. Calcium sulphate
3. Silver chloride
4. Barium sulphate
5. Calcium carbonate
6. Copper(II) carbonate

1. Soluble salts are salts that dissolve in water at room temperature and insoluble salts are
salts that do not dissolve at room temperature.

EXPERIMENT 6.9.2 DESCRIBE THE PREPARATION OF A SOLUBLE SALT THROUGH ACTIVITY
A. Preparation of Soluble Ammonium, Sodium and Potassium Salts
Aim : To prepare soluble salts through a neutralisation reaction between an acid and
an alkali.
Materials : 2.0 mol dm–3 hydrochloric acid, HCl, 2.0 mol dm–3 potassium hydroxide
solution, KOH, phenolphthalein indicator, filter papers and distilled water
Apparatus : 250 cm3 beaker, glass rod, filter funnel, retort stand with clamp, 25 cm3
pipette, pipette filler, burette, evaporating dish, Bunsen burner, pipe clay
triangle, conical flask, tripod stand, white tile and wash bottle

Procedures :
1. Rinse a 25 cm3 pipette with a small amount of 2.0 mol dm–3 potassium hydroxide,
KOH. Then, discard the solution.
2. Pipette accurately 25 cm3 of 2.0 mol dm–3 potassium hydroxide solution, KOH and
transfer into a conical flask.
3. Add a few drops of phenolphthalein indicator and swirl the flask.

Procedures :
4. Rinse a burette with 2.0 mol dm–3 hydrochloric acid, HCl. Then, discard the
solution.
5. Fill the burette with 2.0 mol dm–3 hydrochloric acid, HCl and clamp the burette to
the retort stand. Record the initial reading of the burette.
6. Add acid into the conical flask slowly while swirling it.
7. Continue adding acid until the colour of the solution in the conical flask changes
from pink to colourless

Procedures :
8. Record the final reading of the burette. Then, determine the volume of 2.0 mol
dm–3 hydrochloric acid, HCl required to neutralise 25 cm3 of 2.0 mol dm–3
potassium hydroxide solution, KOH (assuming the acid volume is V cm3 ).
9. Refill a new 25 cm3 of 2.0 mol dm–3 potassium hydroxide solution, KOH into a
conical flask without phenolphthalein indicator.
10. Add V cm3 of 2.0 mol dm–3 hydrochloric acid, HCl from a burette into the conical
flask and swirl the mixture to ensure the mixture is even.

Procedures :
11. Pour the content of the conical flask into an evaporating dish.
12. Heat the solution slowly to evaporate the water so that a saturated solution is
obtained.
13. Let the saturated salt solution cool down to allow crystallisation to occur.

Procedures :
14. Filter the contents of the evaporating dish to obtain potassium chloride crystals,
KCl.
15. Rinse the crystals with a little amount of distilled water.
16. Dry the salt crystals by pressing them between two pieces of filter papers.

Discussion :
1. Why is phenolphthalein indicator needed in titration?
2. Why should not phenolphthalein indicator be added to V cm3 of hydrochloric acid,
HCl to 25 cm3 of potassium hydroxide solution, KOH?
3. Explain why the resulting crystals can only be rinsed with a little amount of
distilled water.
4. Write a balanced chemical equation for this neutralisation reaction.
5. Give two other types of soluble salts that can be prepared by this method

M
TO PREPARE A SOLUBLE SALT BASED ON
THE REACTION BETWEEN AN ACID AND
A METAL OXIDE
B. Preparation of Soluble Salts which are not Ammonium, Sodium and Potassium Salts

Aim : To prepare a soluble salt based on the reaction between an acid and a metal
oxide.
Materials : 2.0 mol dm–3 nitric acid, HNO3, copper(II) oxide powder, CuO, filter papers
and distilled water
Apparatus : 250 cm3 beaker, spatula, glass rod, filter funnel, evaporating dish, Bunsen
burner, pipe clay triangle, conical flask, tripod stand, wash bottle, 20 cm3
measuring cylinder and retort stand with clamp

Procedures :

Procedures :
1. Pour 20 cm3 of 2.0 mol dm–3 nitric acid, HNO3 into a beaker. Heat the acid using
medium heat.
2. Add copper(II) oxide powder, CuO gradually into the acid using a spatula. Stir the
mixture with a glass rod.
3. Continue adding copper(II) oxide, CuO until it is no longer dissolved.

Procedures :
4. Filter the excess copper(II) oxide powder, CuO from the mixture.
5. Pour the filtrate into an evaporating dish and heat the filtrate till a saturated salt
solution is obtained.
6. Allow the saturated solution cool until salt crystals are formed

Procedures :
7. Filter the content of the evaporating dish to obtain the salt crystals. Rinse the
crystals with a little amount of distilled water.
8. Dry the salt crystals by pressing them between two pieces of filter papers.

Discussion :
1. Why is copper(II) oxide, CuO added in excess to the solution?
2. The filtration is done twice in this activity. Explain why.
3. Write a chemical equation for the reaction between nitric acid, HNO3 and
copper(II) oxide, CuO.
4. Is the reaction between nitric acid, HNO3 and copper(II) oxide, CuO also
considered a neutralisation reaction? Give a reason

M
A REACTIVE METAL

Aim : To prepare a soluble salt based on the reaction between an acid and a reactive
metal
Materials : 2.0 mol dm–3 sulphuric acid, H2SO4, zinc powder, Zn, filter paper and
distilled water
burner, pipe clay triangle, conical flask, tripod stand, wash bottle and
retort stand with clamp

Procedures :
1. In pair, study Activity 6.20 on pages 182 and 183. Then, plan the procedures for
the lab activity to prepare soluble salts of zinc sulphate, ZnSO4 based on the
reaction between an acid and a metal.
2. Discuss with your teacher if you encounter any problem when planning the
procedures.

Procedures :
1. Pour 20 cm3 of 2.0 mol dm–3 sulphuri acid, H2SO4 into a beaker.
2. Add zinc powder, Zn gradually into the acid using a spatula. Stir the mixture with
a glass rod.
3. Continue adding zinc powder, Zn until it is no longer dissolved.

Procedures :
4. Filter the excess zinc powder, Zn from the mixture.
6. Allow the saturated solution cool until salt crystals are formed.

Discussion :
1. Does zinc powder, Zn, have to be added in excess to the sulphuric acid, H2SO4?
Why?
2. Write a chemical equation for the reaction between sulphuric acid, H2SO4 and
the metal zinc, Zn.
3. Copper powder is not suitable to prepare copper(II) sulphate salt, CuSO4 by using
the method in this activity. Give the reason why.

M
A METAL CARBONATE.

Aim : To prepare a soluble salt based on the reaction between an acid and a metal
carbonate.
Procedures :
1. In groups, determine a soluble salt that needs to be prepared.
2. Based on the chosen soluble salt, determine the materials and apparatus needed
for this activity.
3. Plan and carry out the activity to prepare the soluble salt based on the reaction
between an acid and an insoluble metal carbonate.

Materials : 2.0 mol dm–3 hydrochloric acid, HCl, magnesium carbonate powder,
MgCO3, filter paper and distilled water
burner, pipeclay triangle, conical flask, tripod stand, wash bottle and retort
stand with clamp

Procedures :
1. In groups, determine a soluble salt that needs to be prepared.
2. Based on the chosen soluble salt, determine the materials and apparatus needed
for this activity.
3. Plan and carry out the activity to prepare the soluble salt based on the reaction
between an acid and an insoluble metal carbonate.

Procedures :
1. Pour 20 cm3 of 2.0 mol dm–3 hydrochloric acid, HCl, into a beaker.
2. Add magnesium carbonate powder, MgCO3 a little at a time while stirring
continuously.
3. Continue adding magnesium carbonate powder, MgCO3 until there is no more
effervescence and it is no longer dissolved.

Procedures :
4. Filter the excess magnesium carbonate powder, MgCO3 from the mixture.
6. Allow the saturated solution cool until salt crystals are formed.

Discussion :
1. Name the gas that is produced.
2. Describe the chemical test for the gas released.
3. Write the chemical equation involved.

M
PURIFICATION OF SOLUBLE SALTS BY
THE RECRYSTALLISATION METHOD

PURIFICATION OF SOLUBLE SALTS BY THE RECRYSTALLISATION METHOD
• The soluble salt produced might contain impurities during preparation.
• Therefore, the soluble salt can be purified by the recrystallisation method.
• Carry out Activity 6.23 to find out how to purify a soluble salt.

TO PURIFY A SOLUBLE SALT USING RECRYSTALLISATION METHOD
Aim : To prepare a pure soluble salt through the recrystallisation method.
Materials : Copper(II) sulphate crystals, CuSO4 , filter papers and distilled water
Apparatus : 250 cm3 beaker, spatula, glass rod, filter funnel, evaporating dish,
Bunsen burner, wire gauze, pipeclay triangle, conical flask, tripod stand,
wash bottle and retort stand with clamp

Procedures :

Procedures :
1. Put the copper(II) sulphate crystals, CuSO4 into a beaker.
2. Add distilled water gradually while stirring. Heat the solution to speed up the
process of dissolving the salt.

Procedures :
3. Filter the hot salt solution to remove insoluble impurities.
4. Then, pour the filtrate into an evaporating dish and heat the filtrate until a
saturated salt solution is obtained.

Procedures :
5. Let the saturated solution cool until salt crystals are formed.
6. Filter the contents of the evaporating dish to get the salt crystals. Rinse the
crystals with a little amount of distilled water.
7. Dry the salt crystals by pressing them between two pieces of filter papers. Make
sure the distilled water added is just enough to dissolve all the crystals.

Discussion :
1. What is the purpose of rinsing the crystals formed with distilled water?
2. State the method used to increase the size of the crystals formed.
3. Can recrystallisation be used to purify insoluble salts? Why?

M
PREPARATION OF INSOLUBLE SALT
Lead(II) iodide, PbI2 Copper(II) carbonate, CuCO3

EXPERIMENT 6.9.3 DESCRIBE THE PREPARATION OF A INSOLUBLE SALT THROUGH ACTIVITY
Preparing Insoluble Salts by Double Decomposition Reaction
• Insoluble salts can be prepared through double decomposition reaction.
• In this process, two salt solutions that contain insoluble salt ions are needed
Soluble salt + Soluble salt  Insoluble salt + Soluble salt

Aim : To prepare an insoluble salt by double decomposition reaction.
Materials : 2.0 mol dm–3 sodium sulphate solution, Na2SO4 , 2.0 mol dm–3
barium chloride solution, BaCl2 , filter papers and distilled water
Apparatus : 250 cm3 beaker, measuring cylinder, glass rod, filter funnel,
evaporating dish, conical flask and wash bottle

Procedures :
1. Based on Figure 6.42, plan the activity with your group members to prepare the insoluble
salt of barium sulphate, BaSO4.
2. Discuss with your teacher if you encounter any problems while planning the procedure.
3. Carry out the activity with your teacher̕
s permission.

Procedures :
1. Pour 25 cm3 of 2.0 mol dm–3 barium chloride solution, BaCl2 into a beaker containing
25 cm3 2.0 mol dm–3 sodium sulphate solution, Na2SO4 .
2. Stir the mixture using a glass rod.

Procedures :
3. Filter the contents of the beaker.
4. Rinse the precipitate (residue) in the filter funnel with distilled water.
5. Dry the precipitate between two sheets of filter paper.

Discussion :
1. Write a balanced chemical equation for the preparation of barium sulphate salt,
BaSO4.
2. Write an ionic equation for the preparation of barium sulphate salt, BaSO4.
3. Why must the filtered barium sulphate salt, BaSO4 precipitate rinsed with distilled
water?
4. In your opinion, is it suitable to prepare barium sulphate salt, BaSO4 based on the
reaction between sulphuric acid, H2SO4 and barium carbonate, BaCO3? Explain
your answer.
5. Name two other salts that can be prepared by the double decomposition reaction.
Then, suggest suitable aqueous solutions for the preparation of the salts
mentioned.

DOUBLE DECOMPOSITION REACTION
• In the double decomposition reaction, the ions in both aqueous solutions exchange
with each other to form a new aqueous solution and a precipitate.
• The ionic equation for the formation of barium sulphate, BaSO4 can be derived
from the balanced chemical equations as shown below :

6.9 PREPARATION OF SALTS

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6.9 PREPARATION OF SALTS