Salts
CLASS- X
13-August-2021
TEXT-1
Preparation and uses of important compounds
Caustic Soda (Sodium Hydroxide, NaOH)
Preparation: In the process of electrolytic decomposition of brine (aqueous solution of sodium chloride), brine decomposes to form sodium hydroxide.
2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)
In this process, chlorine is obtained at anode and hydrogen gas is obtained at cathode as by products. This whole process is known as Chlor – Alkali process.
Uses:
Sodium hydroxide is used for degreasing of metals, manufacturing of paper, soap, detergents, artificial fibres, etc.
Bleaching Powder (Calcium Oxychloride, CaOCl2)
Preparation: Bleaching powder is produced by the action of chlorine on dry slaked lime [Ca(OH)2].
Ca(OH)2 + Cl2→ CaOCl2 + H2O
Uses:
Bleaching powder is used –
(i) for bleaching cotton and linen in the textile industry, for bleaching wood pulp in paper factories and for bleaching washed clothes in laundry;
(ii) as an oxidising agent in many chemical industries; and
(iii) to make drinking water free from germs
Baking Soda (Sodium Hydrogen Carbonate, NaHCO3)
Preparation:
The chemical name of the compound is sodium hydrogen carbonate (NaHCO3). It is produced by the reaction of brine with carbon dioxide and ammonia. This is known as Solvay process.
NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
Ammonium Sodium
chloride hydrogen carbonate
Uses:
(i) Baking soda is used in making of baking powder, which is used in cooking.
Baking powder is a mixture of baking soda (sodium hydrogen carbonate) and a mild edible acid such as tartaric acid. When baking powder is heated or mixed in water, the following reaction takes place –
NaHCO3 + H+ → CO2 + H2O + Sodium salt of acid
(From any acid)
Carbon dioxide produced during the reaction can cause bread or cake to rise making them soft and spongy.
(ii) Baking soda (sodium hydrogen carbonate) is also an ingredient in antacids. Being alkaline, it neutralises excess acid in the stomach and provides relief.
(iii) It is also used in soda-acid fire extinguishers.
TEXT-2
Washing Soda (Sodium Carbonate, Na2CO3.10H2O )
Preparation:
Sodium carbonate is manufactured by the thermal decomposition of sodium hydrogen carbonate obtained by Solvay process.
NaCl + NH3 + H2O + CO2 → NaHCO3 + NH4Cl
NaHCO3 → Na2CO3 + CO2 + H2O
Heat
Na2CO3 + 10 H2O → Na2CO3.10H2O
Uses:
(i) Sodium carbonate (washing soda) is used in glass, soap and paper industries.
(ii) It is used in the manufacture of sodium compounds such as borax.
(iii) Sodium carbonate can be used as a cleaning agent for domestic purposes.
(iv) It is used for removing permanent hardness of water
TEXT-3
Plaster of Paris (Calcium Sulphate Hemihydrate, CaSO4. ½ H2O)
Preparation:
On heating gypsum at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate(CaSO4. ½H2O) which is called Plaster of
Plaster of Paris is a white powder and on mixing with water, it changes to gypsum once again giving a hard solid mass.
CaSO4. ½H2O + 1½H2O → CaSO4.2H2O
(POP) (Gypsum)
