Salts — Formulas and Industrial Uses
~8 min read
- Definition: Salt = product of acid + base neutralisation. NaCl, KCl, CaSO₄ etc.
- Common salts: NaCl (common salt), NaHCO₃ (baking soda), Na₂CO₃ (washing soda), CaOCl₂ (bleaching powder), CaSO₄·½H₂O (plaster of Paris).
- Industrial: Chlor-alkali industry (NaOH, Cl₂, H₂ from brine). Cement uses gypsum.
Salts are everywhere — kitchen, laundry, hospital, construction. CDS/OTA tests common salt names, formulas and industrial preparations.
Types of Salts
- Neutral salts: formed from strong acid + strong base. NaCl (HCl + NaOH).
- Acidic salts: contain replaceable H. NaHSO₄, NaHCO₃ (mild base in solution).
- Basic salts: contain OH or O. Cu(OH)Cl, basic copper carbonate (verdigris).
- Hydrated salts: contain water of crystallisation. CuSO₄·5H₂O (blue vitriol), Na₂CO₃·10H₂O (washing soda).
- Anhydrous salts: water removed on heating. Used as drying agents (e.g., anhydrous CaCl₂).
Important Salts
| Common name | Chemical name / formula | Use |
|---|---|---|
| Common salt | Sodium chloride NaCl | Cooking, preservation, chlor-alkali raw material |
| Baking soda | Sodium bicarbonate NaHCO₃ | Baking (releases CO₂), antacid, fire extinguishers |
| Washing soda | Sodium carbonate Na₂CO₃·10H₂O | Glass, soap, paper industries; softening hard water |
| Bleaching powder | Calcium hypochlorite CaOCl₂ | Disinfection of water, bleaching of textile/paper |
| Plaster of Paris | Calcium sulphate hemihydrate CaSO₄·½H₂O | Casts for fractures, statues, decorative work |
| Gypsum | CaSO₄·2H₂O | Cement-setting retarder, fertiliser |
| Blue vitriol | CuSO₄·5H₂O | Fungicide, electroplating |
| Green vitriol | FeSO₄·7H₂O | Iron supplement, ink, dye |
| Epsom salt | MgSO₄·7H₂O | Laxative; bath salts |
Chlor-Alkali Industry
- Electrolysis of brine (concentrated NaCl solution):
- At cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻ (H₂ released).
- At anode: 2Cl⁻ → Cl₂ + 2e⁻ (Cl₂ released).
- NaOH accumulates in solution.
- Three useful products — NaOH (soaps, paper), Cl₂ (disinfection, PVC) and H₂ (fuel, ammonia synthesis).
CDS/OTA PYQ Examples
Q: Chemical formula of baking soda is:
(a) Na₂CO₃ (b) NaHCO₃ (c) NaOH (d) Na₂SO₄
Answer: (b) NaHCO₃.
Q: Plaster of Paris is:
(a) CaSO₄ (b) CaSO₄·½H₂O (c) CaSO₄·2H₂O (d) CaCO₃
Answer: (b) Calcium sulphate hemihydrate.
Q: Bleaching powder is:
(a) NaOCl (b) CaOCl₂ (c) Ca(OH)₂ (d) NaHCO₃
Answer: (b) Calcium hypochlorite, CaOCl₂.
Q: Washing soda contains how many water molecules of crystallisation?
(a) 2 (b) 5 (c) 7 (d) 10
Answer: (d) 10 — Na₂CO₃·10H₂O.
Drill Salts — Formulas and Industrial Uses for CDS/OTA
CDS/OTA-pattern items on Salts — Formulas and Industrial Uses with answer keys and explanations.
Start Free Mock TestFrequently Asked Questions
Why does baking soda make cakes rise?
On heating it releases CO₂ gas (2NaHCO₃ → Na₂CO₃ + H₂O + CO₂), leavening the dough.
Why is gypsum added to cement?
To retard setting — without it, cement sets too quickly to be useful for construction.
How does Plaster of Paris harden?
It absorbs water and re-forms gypsum: CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O. The process is fast and exothermic.