Q16 of 45 Page 2

What happens when crystals of washing soda are kept open in the air for long time?

When crystals of washing soda (Na2SO4.10H2O) are kept open in the air for long time then the water of crystallization will lose and the crystals will turn to white. This process of loosing water of crystallization when kept in air is called efflorescence.


Na2SO4.10H2O → Na2SO4 + 10H2O

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Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9 respectively.

(a) Which solution is (i) neutral (ii) strongly alkaline (iii) strongly acidic (iv) weakly acidic, and (v) weakly alkaline?


(b) Arrange the pH values in the increasing order of hydrogen ion concentration.

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A milkman adds a very small amount of baking soda to fresh milk.

(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?


(b) Why does this milk take a longer time to set as curd?

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What happens when an acid or a base is added to the water? Why does the beaker appear warm? Why should we always add acid or base to the water and not water to the acid or base?