Equilibrium Question 490

Question: The $ pH $ of a $ {10^{-10}} $ molar $ HCl $ solution is approximately [NCERT 1977]

Options:

A) 10

B) 7

C) 1

D) 14

Show Answer

Answer:

Correct Answer: B

Solution:

$ {10^{-10}}MHCl={10^{-10}},M,[{H^{+}}] $ . But pH $ \ne 10 $ because solution is acidic. This is because $ {H^{+}} $ from $ H_2O({10^{-7}}M) $ cannot be neglected. Total $ [{H^{+}}]={10^{-7}}+{10^{-10}} $

$ ={10^{-7}}+(1+{10^{-3}})={10^{-7}}(1.001) $ That is why $ pH=7 $ (slightly less than 7)



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