Q67 / 180 · AIIMS 2014 · Chemistry

Assertion: Permanent hardness of water is removed by treatment with washing soda. Reason: Washing soda reacts with soluble calcium and magnesium chlorides and sulphates in hard water to form insoluble carbonates.

  • Correct answer
    A
    If both assertion and reason are true and reason is the correct explanation of assertion.
  • B
    If both assertion and reason are true but reason is not the correct explanation of assertion.
  • C
    If assertion is true but reason is false.
  • D
    If both assertion and reason are false.

Solution

$\begin{aligned} & \mathrm{MCl}_2+\mathrm{Na}_2 \mathrm{CO}_3 \rightarrow \mathrm{MCO}_3 \downarrow+2 \mathrm{NaCl} \\ & \mathrm{MSO}_4+\mathrm{Na}_2 \mathrm{CO}_3 \rightarrow M \mathrm{MO}_3 \downarrow+\mathrm{Na}_2 \mathrm{SO}_4 \end{aligned}$ (where, $M=\mathrm{Mg}, \mathrm{Ca}$ )

Hence, the correct answer is option: 'A'.

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