MCQ
Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by 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?
  1. It is an endothermic reaction.
  2. It is an exothermic reaction.
  3. The $pH$ of the resulting solution will be more than seven.
  4. The $pH$ of the resulting solution will be less than seven.
  • A
    $(i)$ and $(ii)$
  • $(ii)$ and $(iii)$
  • C
    $(i)$ and $(iv)$
  • D
    $(iii)$ and $(iv)$

Answer

Correct option: B.
$(ii)$ and $(iii)$
Slaking of lime is an exothermic reaction because a large amount heat is produced during the reaction.
The heat can be felt by touching the beaker from outside. The resulting compound $\mathrm{Ca}(\mathrm{OH})_2$, which is also called slaked lime, turns red litmus solution to blue and hence proves it to be a basic solution. Thus, the $pH$ of this solution will be more than seven.
$\text{CaO}\ +\ \text{H}_2\text{O}\ \xrightarrow{\ \ \ \ \ \ \ \ \ \ \ \ }\text{Ca(OH)}_2\ +\ \text{heat}$
$\ \ \ \ \ \ ^\text{Calcium} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Calcium}$
$\ \ \ \ \ \ \ ^\text{oxide} \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{hydroxide(basic)}$

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