Q60 / 200 · NEET 2007 · Chemistry

Calculate the $\mathrm{pOH}$ of a solution $25^{\circ} \mathrm{C}$ that contains $1 \times 10^{-10} \mathrm{M}$ of hydronium ions i.e. $\mathrm{H}_3 \mathrm{O}^{+}$:

  • Correct answer
    A
    4.000
  • B
    9.000
  • C
    1.000
  • D
    7.000

Solution

Given $\left[\mathrm{H}_3 \mathrm{O}^{+}\right]=1 \times 10^{-10} \mathrm{M}$ at $25^{\circ}\left[\mathrm{H}_3 \mathrm{O}^{+}\right]\left[\mathrm{OH}^{-}\right]=10^{-14}$ $\therefore \quad\left[\mathrm{OH}^{-}\right]=\frac{10^{-14}}{10^{-10}}=10^{-4}$ Now, $\quad\left[\mathrm{OH}^{-}\right]=10^{-p^{\text {OH }}}$ $=10^{-4}=10^{-P^{\mathrm{OH}}}$ $\therefore \quad p^{\mathrm{OH}}=4$.

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

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