6.7 Neutralisation

Short Answer Questions

1. What is neutralisation?
   Answer
   Neutralisation is a chemical reaction where an acid reacts with a base to form salt and water, cancelling out the characteristic properties of both.
2. What ions are involved in the neutralisation process?
   Answer
   Hydrogen ions (H⁺) from the acid and hydroxide ions (OH⁻) from the base.
3. Write the net ionic equation for a neutralisation reaction.
   Answer
   H⁺(aq) + OH⁻(aq) → H₂O(l)
4. What is the pH of a neutral solution?
   Answer
   7
5. What colour does litmus paper turn in a neutral solution?
   Answer
   Purple
6. What happens to hydrogen ion concentration as a solution becomes more acidic?
   Answer
   The hydrogen ion concentration increases.
7. What is titration used for?
   Answer
   Titration is used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.
8. What apparatus is commonly used in titration?
   Answer
   A burette, a pipette, and a conical flask.
9. What is the role of an indicator in titration?
   Answer
   It shows when the reaction has reached the endpoint by changing colour.
10. What formula is used to calculate the unknown concentration in a neutralisation reaction?
    Answer
    M₁V₁/a = M₂V₂/b
11. What products are formed when an acid reacts with a metal hydroxide?
    Answer
    Salt and water.
12. What gas is produced when an acid reacts with a metal carbonate?
    Answer
    Carbon dioxide (CO₂).
13. Give an example of a neutralisation reaction involving a metal oxide.
    Answer
    2HCl(aq) + CuO(s) → CuCl₂(aq) + H₂O(l)
14. What substance is commonly used to neutralise acidic soils in agriculture?
    Answer
    Lime (calcium hydroxide or calcium carbonate).
15. How does an antacid work?
    Answer
    It neutralises excess stomach acid (HCl) using an alkaline substance like magnesium hydroxide.
16. Why is neutralisation important in water treatment?
    Answer
    It adjusts the pH of water to make it safe for consumption and prevent pipe corrosion.
17. What happens at the equivalence point in a titration?
    Answer
    The acid has completely reacted with the base.
18. Name a strong acid that ionises completely in water.
    Answer
    Hydrochloric acid (HCl).
19. What happens when ammonia reacts with an acid?
    Answer
    It forms a salt. Example: HCl(aq) + NH₃(aq) → NH₄Cl(aq).
20. What colour is phenolphthalein in an acidic solution?
    Answer
    Colourless.

Explanation Questions

1. Why does a neutralisation reaction result in a pH closer to 7?
   Answer
   Neutralisation reduces the concentration of H⁺ and OH⁻ ions, forming water, which has a neutral pH of 7.
2. Explain the importance of balancing chemical equations in neutralisation reactions.
   Answer
   Balancing ensures the correct ratio of reactants, so the stoichiometric coefficients are accurate for calculations.
3. How do indicators help in titration experiments?
   Answer
   Indicators change colour at specific pH values, showing when neutralisation is complete.
4. Why does adding an acid to a metal carbonate produce carbon dioxide gas?
   Answer
   The carbonate ions react with hydrogen ions to form CO₂ gas.
5. Why do strong acids ionise completely in water?
   Answer
   They fully dissociate into H⁺ ions and their conjugate bases.
6. How does neutralisation help treat bee stings?
   Answer
   Bee stings contain acid, so applying an alkali like sodium hydrogen carbonate neutralises it.
7. Why is NaOH considered a strong alkali?
   Answer
   It fully ionises in water to release OH⁻ ions.
8. How does industrial neutralisation prevent damage in factories?
   Answer
   It controls pH to prevent corrosion or unwanted chemical reactions.
9. Why is water formed in every neutralisation reaction?
   Answer
   H⁺ from the acid reacts with OH⁻ from the base to form H₂O.
10. How can titration determine unknown molarity?
    Answer
    By measuring the volume of titrant needed to reach the equivalence point and using the formula M₁V₁/a = M₂V₂/b.