Question

What happens when calcium is treated with water?
(i) It does not react with water
(ii) It reacts violently with water
(iii) It reacts less violently with water
(iv) Bubbles of hydrogen gas formed stick to the surface of calcium
A. (i) and (iv)
B. (ii) and (iii)
C. (i) and (iii)
D. (iii) and (iv)

Answer 1

Hint: In the electrochemical series, calcium is placed much above than the hydrogen. This means that calcium is a strong reducing agent and can easily reduce hydrogen. It replaces the hydrogen gas from its compound and forms its own bonds with the other atoms, liberating hydrogen gas.

Complete step by step answer:
When a metal is reacted with water, it generally forms a metal hydroxide and liberates the hydrogen gas. Thus, the general reaction of a metal with the water is as follows:
Metal + Water $ \to $ Metal hydroxide + hydrogen gas
In general, metals form a metal oxide and hydrogen gas and this metal oxide when soluble in water dissolves further forming a metal hydroxide. But some metals form metal hydroxide directly.
In the case of the reaction of calcium with water, we get calcium hydroxide and hydrogen gas is liberated which forms the bubbles that stick to the surface of the calcium which is a solid. The reaction of calcium is less violent with water. The general reaction is as follows:
$C{a_{(s)}} + 2{H_2}{O_{(l)}} \to Ca{(OH)_{2(aq)}} + {H_{2(g)}}$

Thus, the correct option is D. (iii) and (iv).

Note:
This is an important method for the production of lime water. Limewater may also be prepared by mixing calcium hydroxide (\[Ca{\left( {OH} \right)_2}\] ) with water and removing excess undissolved solute (e.g. by filtration). When excess calcium hydroxide is added (or when environmental conditions are altered, e.g. when its temperature is raised sufficiently), a milky solution results due to the homogeneous suspension of excess calcium hydroxide. This liquid has been known traditionally as milk of lime.