Equilibrium Question 313
Question: The hydrogen ion concentration of a $ 0.006M $ benzoic acid solution is $ (K_{a}=6\times {10^{-5}}) $ [MP PET 1994]
Options:
A) $ 0.6\times {10^{-4}} $
B) $ 6\times {10^{-4}} $
C) $ 6\times {10^{-5}} $
D) $ 3.6\times {10^{-4}} $
Show Answer
Answer:
Correct Answer: B
Solution:
Initial concentration = 0.006 M
Þ $ K_{a}=6\times {10^{-5}} $ equilibrium reaction. $ \underset{C(1-a),}{\mathop{\underset{C}{\mathop{C_6H_5COOH}},}}, $ ⇌ $ \underset{Ca}{\mathop{\underset{O}{\mathop{C_6H_5CO{O^{-}}}},}},+\underset{Ca}{\mathop{\underset{Oinitial}{\mathop{{H^{+}},}},}}, $
$ K_{a}=C{{\alpha }^{2}} $
$ (\because 1-\alpha \approx 1) $ for weak electrolyte $ \alpha =\sqrt{\frac{K_{a}}{C}} $ ; $ \alpha =\sqrt{\frac{6\times {10^{-5}}}{0.006}} $ ; $ \alpha ={10^{-1}} $
$ \because ,[{H^{+}}]=C\alpha $
$ =0.006\times {10^{-1}} $
$ =6\times {10^{-4}} $ M.
