Q21 of 30 Page 34

Why alkalis like sodium hydroxide and potassium hydroxide should not be left exposed to air?

Alkalis like sodium hydroxide and potassium hydroxide should not be left exposed to air because when sodium carbonate reacts with CO2 present in the air form sodium carbonate and when potassium hydroxide reacts with CO2 present in the air form potassium carbonate.


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19

A solution of alcohol in water has been prepared by mixing 150 ml of alcohol with 600 ml of water. Calculate the volume percentage of the solution.

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Why is plaster of Paris written as CaSO4 . 1/2 H2O? How is it possible to have half a water molecule attached to CuSO4?

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What happens when crystals of washing soda are left open in dry air? What is this change named as? Name two industries based on the use of washing soda.

 23

(i) Write the chemical equation to represent the action of atmospheric CO2 gas and bleaching powder when left exposed in the open. (ii) State for what purpose bleaching powder is used in water treatment plants. (iii) Why does bleaching powder smell of chlorine when exposed to air?