A) \[{{10}^{-7}}\]
B) \[{{10}^{-5}}\]
C) \[{{10}^{-10}}\]
D) \[{{10}^{-8}}\]
Correct Answer: C
Solution :
Key Idea: \[pH=-\log \sqrt{{{K}_{a}}\times C}\] Given \[pH=5,\,C=1\,M\] \[\therefore \] \[pH-\log \sqrt{{{K}_{a}}\times 1}\] or \[5=-\log \sqrt{{{K}_{a}}}\] or \[5=-\frac{1}{2}\log \,{{K}_{a}}\] or \[\log {{K}_{a}}=10\] \[\therefore \] \[{{K}_{a}}={{10}^{-10}}\]
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