Calculate $\left[\mathrm{H}_3 \mathrm{O}^{+}\right]$in 0.02 M solution of monobasic acid if dissociation…

Calculate $\left[\mathrm{H}_3 \mathrm{O}^{+}\right]$in 0.02 M solution of monobasic acid if dissociation constant is $1.8 \times 10^{-5}$.
  1. $\quad 3.0 \times 10^{-4} \mathrm{M}$
  2. $6.0 \times 10^{-4} \mathrm{M}$
  3. $2.0 \times 10^{-4} \mathrm{M}$
  4. $4.0 \times 10^{-4} \mathrm{M}$

Solution

For a weak monobasic acid, $\begin{aligned} \therefore \quad & \alpha=\sqrt{\frac{\mathrm{K}_{\mathrm{a}}}{\mathrm{c}}}=\sqrt{\frac{1.8 \times 10^{-5}}{0.02}}=3 \times 10^{-2} \\ & {\left[\mathrm{H}_3 \mathrm{O}^{+}\right]=\alpha \mathrm{c}=3 \times 10^{-2} \times 0.02=6.0 \times 10^{-4} \mathrm{M} } \end{aligned}$

Asked in: MHT CET 2024 (03 May Shift 1)

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