Question

What is the $pH$ of $0.01\, M$ glycine solution? For glycine $K_{a_1} = 4.5 \times 10^{-3}$ and $K_{a_2} = 1.7 \times 10^{-10}$ at $298 \,K$.

• A. 3.0
• B. 10.0
• C. 7. 1
• D. 8.2

Answer 1

Answer: (C)

$ K=K_{a_{1}} \times K_{a_{2}} =4.5 \times 10^{-3} \times 1.7 \times 10^{-10}$
$=7.65 \times 10^{-13} $
$\left[ H ^{+}\right] =\sqrt{K \cdot C} $
$=\sqrt{7.65 \times 10^{-13} \times 0.01}$
$=8.7 \times 10^{-8} $
$ pH =-\log \left[ H ^{+}\right]=-\log 8.7 \times 10^{-8} $
$=-\left(\log 10^{-8}+\log 8.7\right) $
$=8-0.93 $
$ \Rightarrow =7.07$