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Chemistry Question on Expressing Concentration of Solutions

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

A

3×10−103\times 10^{-10}

B

5×10−10 5\times 10^{-10}

C

1×10−10 1\times 10^{-10}

D

5×10−25\times 10^{-2}

Answer

5×10−10 5\times 10^{-10}

Explanation

Solution

pH=−log⁡10[H+]pH =-\log _{10}\left[ H ^{+}\right] or log⁡10[H+]=−4.7 \log _{10}\left[ H ^{+}\right]=-4.7 [H+]=10−4.7\left[ H ^{+}\right] =10^{-4.7} =10−5×10+0.3=10^{-5} \times 10^{+0.3} =10−5×=10^{-5} \times anti log⁡0.3\log 0.3 =2×10−5=2 \times 10^{-5} Kw=[H+][OH−]K_{w} =\left[ H ^{+}\right]\left[ OH ^{-}\right] [OH−]=Kw[H+]=10−142×10−5\left[ OH ^{-}\right] =\frac{K_{w}}{\left[ H ^{+}\right]}=\frac{10^{-14}}{2 \times 10^{-5}} =0.5×10−9=5×10−10 =0.5 \times 10^{-9}=5 \times 10^{-10}