Question

Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by the liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed?
(i) It is an endothermic reaction.
(ii) It is an exothermic reaction.
(iii) The pH of the resulting solution will be more than seven.
(iv) The pH of the resulting solution will be less than seven.

• A. (i) and (ii)
• B. (ii) and (iii)
• C. (i) and (iv)
• D. (iii) and (iv)

Answer 1

Answer: (B)

(ii) and (iii)

Quick lime(CaO) combines with water to form calcium hydroxide($Ca(OH{)}_2$). It is an exothermic reaction as heat is produced in the reaction.
$CaO+H_{2}O\to Ca(OH{)}_2+heat$

On adding excess of calcium hydroxide in water, a saturated solution of calcium hydroxide is formed which is called lime water. Lime water is basic in nature and therefore has a pH above 7.