Equilibrium Question 811
Question: Calculate the pH of a solution containing 0.1 M
$ HCO_3^{-} $ and $ 0.2,M,CO_3^{2-} $
$ [K_1(H_2CO_3^{-})=4.2\times {10^{-7}}\times 10 $ and $ K_2(HCO_3^{-})=4.8\times {10^{-11}}]. $
Options:
A) 3.18
B) 10.62
C) 6.62
D) 9.31
Show Answer
Answer:
Correct Answer: B
Solution:
$ HCO_3^{-}\to {H^{+}}+CO_3^{2-} $
$ K_2=\frac{[{H^{+}}][CO_3^{2-}]}{[HCO_3^{-}]}=4.8\times {10^{-11}} $
$ =4.8\times {10^{-11}}(0.1/0.2) $
$ pH=-\log [{H^{+}}] $
$ =-log( 4.8\times {10^{-11}}\times 0.5 )=10.62 $
