6.9 Preparation of Salts

Short Answer Questions

1. What is the general reaction equation for the neutralisation method of preparing salts?
   Answer
   Acid + Alkali → Salt + Water
2. Give an example of a neutralisation reaction that forms a soluble salt.
   Answer
   HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
3. What type of metal reacts with acids to produce a salt and hydrogen gas?
   Answer
   Reactive metals.
4. Write the balanced chemical equation for the reaction of zinc with hydrochloric acid.
   Answer
   2HCl(aq) + Zn(s) → ZnCl₂(aq) + H₂(g)
5. What are the products when an acid reacts with a metal carbonate?
   Answer
   A salt, water, and carbon dioxide.
6. Give an example of an acid reacting with a metal carbonate to form a soluble salt.
   Answer
   2HCl(aq) + CaCO₃(s) → CaCl₂(aq) + H₂O(l) + CO₂(g)
7. What is precipitation in salt preparation?
   Answer
   The formation of an insoluble salt when two soluble salt solutions are mixed.
8. Write a chemical equation for the precipitation of barium sulfate.
   Answer
   BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)
9. How is an insoluble salt separated from a reaction mixture?
   Answer
   By filtration.
10. What is the purpose of crystallisation in salt preparation?
    Answer
    To obtain pure solid salt crystals from a solution.
11. What are the two main methods used to prepare soluble salts?
    Answer
    Neutralisation and reaction with metals, metal oxides, or metal carbonates.
12. What is the role of cooling in the crystallisation process?
    Answer
    It decreases the solubility of the salt, allowing crystals to form.
13. What happens when lead(II) nitrate and potassium iodide solutions are mixed?
    Answer
    Lead(II) iodide (PbI₂) precipitates out.
14. Write the equation for the formation of lead(II) iodide.
    Answer
    Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq)
15. What is the final step in the preparation of an insoluble salt?
    Answer
    Drying the salt.
16. Which factors affect the crystal size in crystallisation?
    Answer
    The rate of cooling and the concentration of the solution.
17. What is recrystallisation used for?
    Answer
    Purifying salt crystals by dissolving them in a hot solvent and cooling.
18. What determines the shape of a salt crystal?
    Answer
    The nature of the salt and the conditions of crystallisation.
19. Why do salts form crystalline structures?
    Answer
    Because of the orderly arrangement of ions in a lattice.

Explanation Questions

1. Why do neutralisation reactions produce soluble salts?
   Answer
   The reaction forms water and a salt, which remains dissolved in the solution.
2. Why is hydrogen gas released when a reactive metal reacts with an acid?
   Answer
   The metal displaces hydrogen ions, forming hydrogen gas.
3. Why does the reaction between acids and metal oxides produce water?
   Answer
   The oxide ions (O²⁻) combine with hydrogen ions (H⁺) to form water (H₂O).
4. How can crystallisation be used to purify salts?
   Answer
   Impurities remain in solution while pure salt crystals form as the solution cools.
5. Why do different salts form different crystal shapes?
   Answer
   The arrangement of ions in the lattice varies based on their size and charge.
6. Why is slow cooling important in crystallisation?
   Answer
   Slow cooling allows larger, well-formed crystals to develop.
7. Why do precipitates form in double decomposition reactions?
   Answer
   The new salt formed is insoluble and separates as a solid.
8. How does washing improve the purity of precipitated salts?
   Answer
   It removes any soluble impurities left on the surface of the salt crystals.
9. What determines whether a salt is soluble or insoluble?
   Answer
   The interactions between the salt’s ions and water molecules.
10. Why do we use filtration in the preparation of insoluble salts?
    Answer
    To separate the solid precipitate from the liquid solution.