Seawater contains many salts dissolved in it. Common salt is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt and is mined like coal. The common salt is an important raw material for chemicals of daily use.
Read the passage carefully and answer the questions that follow.
Generated by claude-sonnet-4-6 · 2026-06-15 06:43 · grounding stimulus
Model Answer
(a) Electrolysis of brine (aqueous NaCl solution):
$$2NaCl(aq) + 2H_2O(l) \rightarrow 2NaOH(aq) + Cl_2(g) + H_2(g)$$
(b) Uses of Chlorine (Cl₂):
- Used as a disinfectant for purification of drinking water.
- Used in the manufacture of PVC and disinfectants.
(Or uses of NaOH: used in making soap; used in paper industry.)
(c) Brine is a concentrated aqueous solution of common salt (NaCl). When electricity is passed through brine, it undergoes electrolysis to produce three important chemicals — sodium hydroxide (NaOH), chlorine gas, and hydrogen gas. This process is called the chlor-alkali process. These products are widely used in industries such as soap-making, textile, and water treatment.
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Explanation
- (a) Examiners expect a fully balanced equation with state symbols — don't skip those.
- (b) Name ONE product clearly and give TWO distinct uses. Chlorine or NaOH are the safest choices as their uses are explicitly in the textbook.
- (c) Sub-question (c) appears to be cut off in the original, so the answer covers the chlor-alkali process — the most likely intended topic given the passage. In the exam, answer whatever the actual question asks. Key terms: chlor-alkali process, brine, electrolysis — examiners look for these.