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Chemical Reactions and Equations — Science STD 10 — Question

CBSE BoardEnglish MediumSTD 10ScienceChemical Reactions and Equations1 Mark
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)
  • B
    (ii) and (iii)
  • C
    (i) and (iv)
  • D
    (iii) and (iv)
✓

Answer

  1. (ii) and (iii)

Explanation:

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 Ca(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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