Common salt (NaCl) is not used as a raw material for preparation of which one of the following compounds?
- (a)Bleaching powder
- (b)Baking soda
- (c)Plaster of Paris
- (d)Washing soda
Correct — C, Plaster of Paris. Plaster of Paris (calcium sulphate hemihydrate, CaSO₄·½H₂O) is made by heating the mineral gypsum (CaSO₄·2H₂O), a calcium compound with no sodium chloride involved. The other three all trace back to common salt: baking soda (NaHCO₃) and washing soda (Na₂CO₃) are made from brine by the Solvay process, and bleaching powder is made by passing chlorine — obtained from the electrolysis of brine — over slaked lime. Only Plaster of Paris does not use NaCl as a raw material.
- (a)Bleaching powder — Bleaching powder (calcium oxychloride) is made by the action of chlorine on slaked lime; the chlorine comes from the electrolysis of brine (NaCl solution), so common salt is a raw material.
- (b)Baking soda — Baking soda (sodium bicarbonate, NaHCO₃) is produced from brine in the Solvay process, so sodium chloride is one of its raw materials.
- (d)Washing soda — Washing soda (sodium carbonate, Na₂CO₃) is obtained by heating the sodium bicarbonate made from brine in the Solvay process, so it too starts from common salt.
Common salt (NaCl) is the feedstock of the chlor-alkali and Solvay industries: electrolysis of brine yields chlorine, hydrogen and sodium hydroxide, while the Solvay (ammonia-soda) process converts brine into sodium bicarbonate and then sodium carbonate. Plaster of Paris, by contrast, is a calcium compound made from gypsum and contains no sodium or chlorine.
Group the products by their key element: baking soda, washing soda and (via chlorine) bleaching powder are all salt-derived and share NaCl as a raw material. Plaster of Paris is the outlier because it is calcium sulphate from gypsum — the trick is spotting the compound with no link to sodium chloride.
- Plaster of Paris (CaSO₄·½H₂O) is made by heating gypsum (CaSO₄·2H₂O); no NaCl is used.
- Baking soda (NaHCO₃) and washing soda (Na₂CO₃) come from brine via the Solvay process.
- Bleaching powder uses chlorine (from electrolysis of brine) plus slaked lime.
- Electrolysis of brine (the chlor-alkali process) yields NaOH, Cl₂ and H₂.
- Assuming every household chemical comes from salt — Plaster of Paris comes from gypsum.
- Confusing washing soda (Na₂CO₃) with baking soda (NaHCO₃).
Asked as 'which is/ is not made from common salt' or by matching chemicals to their raw materials and processes.
Consider the following statements: 1. Baking soda is used in fire extinguishers. 2. Quicklime is used in the manufacture of glass. 3. Gypsum is used in the manufacture of Plaster of Paris. Which of the statements given above is/are correct?
- (a) 1 and 2
- (b) 2 and 3
- (c) 1 only
- (d) 1, 2 and 3
Answer(d) 1, 2 and 3
Same concept — confirms that Plaster of Paris is manufactured from gypsum (statement 3), the very reason common salt is not its raw material.
NDA_GAT_2021_II_Q1442021Which one of the following is the chemical formula of Plaster of Paris?
- (a) CaSO₄·½ H₂O
- (b) CaSO₄·2 H₂O
- (c) CaSO₄·5 H₂O
- (d) CaSO₄·4 H₂O
Answer(a) CaSO₄·½ H₂O
Same concept — the chemical identity of Plaster of Paris (CaSO₄·½H₂O), a calcium sulphate from gypsum, reinforcing that it contains no sodium chloride.
Match List I (Chemical Name) with List II (Chemical Formula): A. Washing soda; B. Baking soda; C. Bleaching powder; D. Gypsum. List II: 1. CaOCl2; 2. NaHCO3; 3. Na2CO3.10H2O; 4. CaSO4.2H2O.
- (a) 4 2 1 3
- (b) 4 1 2 3
- (c) 3 1 2 4
- (d) 3 2 1 4
Answer(d) 3 2 1 4
- practice — not a real PYQ
Which one of the following is the raw material for the manufacture of Plaster of Paris?
- (a)Common salt
- (b)Limestone
- (c)Gypsum
- (d)Bauxite
Answer(c) Gypsum — heated to give calcium sulphate hemihydrate (CaSO₄·½H₂O).
- practice — not a real PYQ
Which process uses common salt (brine) to manufacture washing soda?
- (a)Contact process
- (b)Solvay process
- (c)Haber process
- (d)Bessemer process
Answer(b) Solvay process — the ammonia-soda process that converts brine to Na₂CO₃.