Chemical and Ionic Equilibrium 2 Question 15

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15. $\mathrm{CH}{3} \mathrm{NH}{2}\left(0.1\right.mole,\left.K_{b}=5 \times 10^{-4}\right)isaddedto0.08moleof\mathrm{HCl}$ and the solution is diluted to one litre, resulting hydrogen ion concentration is

======= ####15. $\mathrm{CH}{3} \mathrm{NH}{2}\left(0.1\right.mole,\left.K_{b}=5 \times 10^{-4}\right)isaddedto0.08moleof\mathrm{HCl}$ and the solution is diluted to one litre, resulting hydrogen ion concentration is

3e0f7ab6f6a50373c3f2dbda6ca2533482a77bed (a) 1.6×1011

(b) 8×1011

(c) 5×105

(d) 8×102

(2005,1M)

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Solution:

$$ \mathrm{CH}{3} \mathrm{NH}{2}+\mathrm{HCl} \longrightarrow \mathrm{CH}{3} \mathrm{NH}{3}^{+}+\mathrm{Cl}^{-} $$

Initial : 0.100.0800

 Final : 0.0200.080.08

$\mathrm{pOH}=\mathrm{p} K_{b}+\log \frac{\left[\mathrm{CH}{3} \mathrm{NH}{3}^{+}\right]}{\left[\mathrm{CH}{3} \mathrm{NH}{2}\right]}$

=log(5×104)+log0.080.02=3.9

pH=14pOH=10.1

[H+]=8×1011