Vidaara.orgClass 10 · Chemistry
CodeVID-C10-02-T3-01
Salts — Preparation, Properties & Uses — Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Write chemical formulae and balanced equations wherever asked.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
Which salt gives a neutral aqueous solution?
- A.NH₄Cl
- B.Na₂CO₃
- C.NaCl
- D.CH₃COONa
2.
Bleaching powder is chemically:
- A.CaSO₄
- B.CaOCl₂
- C.CaCO₃
- D.Ca(OH)₂
3.
Baking soda is:
- A.Na₂CO₃
- B.NaHCO₃
- C.NaOH
- D.NaCl
4.
Plaster of Paris is obtained by heating:
- A.limestone
- B.gypsum
- C.marble
- D.chalk
5.
Anhydrous copper sulphate is:
- A.blue
- B.green
- C.white
- D.black
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
What is water of crystallisation? Give one example.
7.
Write the formula and one use of washing soda.
8.
Why is sodium hydrogencarbonate used in fire extinguishers?
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Explain the chlor-alkali process, naming the three products and one use of each.
10.
How is plaster of Paris prepared from gypsum? Why is it stored in a moisture-proof container?
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Describe the preparation, one important property and two uses each of baking soda and bleaching powder.
Answer Key
Section A — Multiple Choice Questions
- (C) NaCl
- (B) CaOCl₂
- (B) NaHCO₃
- (B) gypsum
- (C) white
Section B — Short Answer (2 marks)
- Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt crystal; for example, copper sulphate crystals are CuSO4.5H2O (five water molecules).
- Washing soda is Na2CO3.10H2O; it is used to remove the permanent hardness of water (and in the glass and soap industries).
- On heating, NaHCO3 produces carbon dioxide, a heavy non-combustible gas that covers the fire and cuts off oxygen, putting out the flames.
Section C — Short Answer (3 marks)
- Passing electricity through concentrated brine: 2NaCl + 2H2O gives 2NaOH + Cl2 + H2. NaOH is used to make soap and paper; Cl2 is used to make bleaching powder and disinfect water; H2 is used as a fuel and in making ammonia.
- Gypsum (CaSO4.2H2O) is heated to about 100 degrees Celsius to give POP, CaSO4.half H2O. It is kept moisture-proof because absorbing water makes it set into hard gypsum, so it would no longer be usable.
Section D — Long Answer (5 marks)
- Baking soda (NaHCO3): prepared from brine, NaCl + H2O + CO2 + NH3 gives NaHCO3 + NH4Cl. Property: it is a mild base and on heating gives CO2 and Na2CO3. Uses: as an antacid to relieve acidity, and in baking (it releases CO2 to make cakes rise); also in fire extinguishers. Bleaching powder (CaOCl2): prepared by passing chlorine over dry slaked lime, Ca(OH)2 + Cl2 gives CaOCl2 + H2O. Property: it releases chlorine, which acts as a bleaching and oxidising agent. Uses: to bleach cotton, linen and paper, and to disinfect drinking water.
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