Q43 / 180 · AIIMS 2017 · Chemistry

$\mathrm{ZnO}$ is white when cold and yellow when heated. It is due to the development of

  • A
    $\mathrm{Na}_2 \mathrm{CO}_3+\mathrm{NaOH}$
  • B
    $\mathrm{NaHCO}_3+\mathrm{Na}_2 \mathrm{CO}_3$
  • Correct answer
    C
    $\mathrm{NaHCO}_3+\mathrm{NaOH}$
  • D
    $\mathrm{NaOH}+\mathrm{NaCl}$

Solution

$\mathrm{NaHCO}_3$ is a sodium salt of weak acid, while $\mathrm{NaOH}$ is a strong base so, they react and cannot exist together in solution. $\mathrm{NaHCO}_3+\mathrm{NaOH} \longrightarrow \mathrm{Na}_2 \mathrm{CO}_3+\mathrm{H}_2 \mathrm{O}$

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

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