Question

An alcoholic drinks substance $ pH=4.7 $ then $ ^{-}OH $ ion concentration of this solution is:

• A. $ 3\times 10^{-10} $
• B. $ 5\times 10^{-10}$
• C. $ 1\times 10^{-10}$
• D. $ 5\times 10^{-2} $

Answer 1

The Correct Option is B

$pH =-\log _{10}\left[ H ^{+}\right] $ or $ \log _{10}\left[ H ^{+}\right]=-4.7$ $\left[ H ^{+}\right] =10^{-4.7} $ $=10^{-5} \times 10^{+0.3} $ $=10^{-5} \times $ anti $ \log 0.3 $ $=2 \times 10^{-5} $ $ K_{w} =\left[ H ^{+}\right]\left[ OH ^{-}\right] $ $\left[ OH ^{-}\right] =\frac{K_{w}}{\left[ H ^{+}\right]}=\frac{10^{-14}}{2 \times 10^{-5}} $ $ =0.5 \times 10^{-9}=5 \times 10^{-10}$