Preparing Soluble Salts

Preparation of Soluble Salts

  1. There are 2 things to be considered when preparing a salt:
    1. What are the chemical used?
    2. How to separate the salt from other substance?
  2. Method used to prepare salt depends on the solubility of the salt.
  3. Soluble salts are prepared from the reactions between an acid with a metal/ base/ metal carbonate.
  4. Diagram below shows the chemical reaction that can be used to prepare the soluble salts.

Example:
Write chemical equation(s) for the reaction that can be used to prepare the following salts.

  1. Sodium Chloride
  2. Ammonium Nitrate
  3. Potassium sulphate
  4. Zinc Sulphate (3 equations)
  5. Lead(II) nitrate(3 equations)
  6. Copper sulphate(2 equations)

Answer:
a. Sodium Chloride

NaOH + HCl → NaCl + H2O

b. Ammonium Nitrate

NH3 + HNO3 → NH4NO3

c. Potassium sulphate

KOH + H2SO4 → K2SO4 + H2O

d. Zinc Sulphate (3 equations)

ZnO +  H2SO4 → ZnSO4 + H2O
Zn  + H2SO4 → ZnSO4 + H2
ZnCO3  + H2SO4 → ZnSO4 + H2O + CO2

e. Lead(II) nitrate(3 equations)

PbO +  2HNO3 → Pb(NO3)2 + H2O
Pb  + 2HNO3 → Pb(NO3)2 + H2
PbCO3  + 2HNO3 → Pb(NO3)2 + H2O + CO2

f. Copper sulphate(2 equations)

CuO +  H2SO4 → CuSO4 + H2O
CuCO3  + H2SO4 → CuSO4 + H2O + CO2

Preparing Salts of Potassium, Sodium and Ammonium

  1. Potassium, sodium and ammonium salts are usually prepared through the reactions of acids with alkalis.
  2. Reaction acid with alkali will produce salt and water.
    Acid + Alkali → Salt + Water
  3. The salt is prepared by titration method of acid and alkali using an indicator.

Steps to Prepare the Salts of Potassium, Sodium and Ammonium through Titration

Step 1 – Titration to Find the End Point

  1. The end point is the point in a titration at which the 2 reactants have completely reacted. 
  2. An endpoint is often marked by a color change.

Step 2 – Titrate Without Indicator

  1. The product obtain in step 1 is contaminate by the indicator.
  2. The reaction is repeated by using the same amount of reactants as in step 1, without using any indicator.

Step 3 – Crystalisation

Step 4 – Filtration and Drying

Preparing Salts of Non-“Potassium, Sodium and Ammonium”

  1. The salt non-potassium, sodium and ammonium is prepared by reacting acid with insoluble metal/metal oxide/metal carbonate:
    1. Acid + Metal Salt + Hydrogen (Displacement reaction)
    2. Acid + Metal oxide Salt + Water (Neutralisation Reaction)
    3. Acid + Metal carbonate Salt + Water + Carbon Dioxide
  2. Below is the steps in preparing the soluble non-potassium, sodium and ammonium salts.

Step 1 – The Reaction

Add metal/metal oxide/metal carbonate powder until excess into a fixed volume of the heated acid

Step 2 – Filtration 1 to Remove Excess Reactant

Filter the mixture to remove excess metal/metal oxide/metal carbonate

Step 3 – Crystalisation

  1. Evaporate the filtrate until it becomes a saturated solution
  2. Dip in a glass rod, if crystals are formed, the solution is saturated.

Step 4 – Filtration 2 to Collect the Solid Salt

  1. Cooled at room temperature
  2. Filter and dry the salt crystals by pressing them between filter papers.

Preparing Insoluble Salts

  1. Insoluble salts can be made by ionic precipitation (is also called double decomposition/double displacement).
  2. This involves mixing a solution that contains its positive ions with another solution that contains its negative ions.

Example:
Write the equation of the reaction that can be used to prepare the following salt:

  1. Calcium sulphate
  2. Lead chloride
  3. Copper carbonate

Answer:
a. Calcium sulphate

CaCl2 + NaSO4 → CaSO4 + 2NaCl
Ca(NO3)2 + ZnSO4 → CaSO4 + Zn(NO3)2

b. Lead chloride

Pb(NO3)2 + 2NaCl → PbCl2 + 2NaNO3

c. Copper carbonate

CuSO4 + Na2CO3 → CuCO3 + Na2SO4

CuCl2 + K2CO3 → CuCO3 + 2KCl
Cu(NO3)2 + Na2CO3 → CuCO3 + 2NaNO3