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)
