We know that chlorine is produced during the electrolysis of aqueous sodium chloride (brine). This chlorine gas is used for the manufacture of bleaching powder. Bleaching powder is produced by the action of chlorine on dry slaked lime [Ca(OH)2]. Bleaching powder is represented as CaOCl2, though the actual composition is quite complex.
Preparation of Bleaching Powder
(a) For bleaching cotton and linen in the textile industry, for bleaching wood pulp in paper factories and for bleaching washed clothes in laundry.
(b) As an oxidising agent in many chemical industries, and
(c) For disinfecting drinking water to make it free of germs.
The chemical name of baking soda is sodium hydrogen carbonate or sodium bicarbonate. Baking soda (or sodium bicarbonate) is represented by the formula NaHCO3. The soda commonly used in the kitchen for making tasty crispy pakoras is baking soda. Some time it is added for faster cooking. It is produced using sodium chloride as one of the raw materials.
It can be used to neutralise an acid because it is mild non-corrosive base due to the hydrolysis of HCO3- ion.
The following reaction takes place when it is heated during cooking.
Carbon dioxide so produced during the reaction is responsible for making the bread and cake to rise making them soft and spongy.
(b) As an ingredient in antacids. Being alkaline, it neutralises excess acid in the stomach and provides relief.
(c) It is used in soda-acid fire extinguisher.
Step-I
The CO2 required in this reaction is obtained by heating limestone.
Step-II Dry sodium hydrogencarbonate is heated strongly to produce sodium carbonate.
Step-III Washing soda (Na2CO3.10H2O) is obtained by crystallisation from a saturated solution of soda ash (Na2CO3)
Manufacturing Process of Sodium Carbonate (Solvay Process)
(b) Washing soda is used for softening hard water.
(c) Sodium carbonate (soda ash) is used for the manufacture of detergents.
(d) Sodium carbonate is used for the manufacture of many important compounds, such as borax (Na2B4O7), Hypo (Na2S2O3.5H2O), etc.
(e) Sodium carbonate is also used in paper and paint industries.
It is fixed number of water molecules present in crystalline salt,
Example:
Hydrous to Anhydrous Copper Sulphate
In plaster of paris one molecule of water is shared by two CaSO4 as
Preparation of Plaster of Paris
Plaster of paris is obtained by heating gypsum (CaSO4.2H2O) at 373K (or 100°C).
or
During the preparation of plaster of paris, temperature should be controlled carefully. Otherwise, anhydrous calcium sulphate (CaSO4) will be formed. Anhydrous calcium sulphate does not set into hard mass when mixed with water. So, if temperature is not controlled carefully, the plaster of paris obtained will have poor setting property. Sculptures using Plaster of Paris
Properties of Plaster Paris
Uses of Plaster of Paris
Efflorescence
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1. Are the crystals of salts really dry? |
2. What is efflorescence? |
3. What is deliquescence? |
4. What are hygroscopic substances? |
5. What is the significance of water of crystallization in salts like Plaster of Paris? |
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