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 $



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