Q27 / 155 · WBJEE 2024 · Chemistry

What will be the change in acidity if (i) $\mathrm{CuSO}_4$ is added in saturated $\left(\mathrm{NH}_4\right)_2 \mathrm{SO}_4$ solution (ii) $\mathrm{SbF}_5$ is added in anhydrous HF

  • Correct answer
    A
    increase, increase
  • B
    decrease, decrease
  • C
    increase, decrease
  • D
    decrease, increase

Solution

Hint : i) $\mathrm{Cu}^{2+}{ }_{(\mathrm{aq})}+4 \mathrm{NH}_4{ }^{+}{ }_{(\mathrm{aq})} \rightarrow\left[\mathrm{Cu}\left(\mathrm{NH}_3\right)_4\right]^{+2}+4 \mathrm{H}^{+}{ }_{(\mathrm{aq})}$ Formation of stable $\left[\mathrm{Cu}\left(\mathrm{NH}_3\right)_4\right]^{+2}$ complex increases $\mathrm{H}^{+}$ion concentration, thus acidity increases ii) $\mathrm{HF}+\mathrm{HF} \rightleftharpoons \mathrm{H}_2 \mathrm{~F}^{+}+\mathrm{F}^{-}$ $\mathrm{SbF}_5$ removes $\mathrm{F}^{-}$as $\mathrm{SbF}_6{ }^{-}$and shifts equilibrium forward to increase $\mathrm{H}_2 \mathrm{~F}^{+}$

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

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