Question

What is the resultant pH of the solution if equal volumes of two solutions with pH=6 and pH=8 are mixed?
( log 5.5 = 0.740 )

• A. 7
• B. 6.29
• C. 7.5
• D. 8.29

Answer 1

The correct option is A 7

Let us take the case of 1 litre solution.
For $pH=6$
We know that $pH=-lo{g}_{10}\left[H^{+}\right]6=-lo{g}_{10}\left[H^{+}\right][H^{+}{]}_{1^{st}solution}={10}^{-6}mol{L}^{-1}Numberof{H}^{+}ionsin1Lsolution={10}^{-6}\times 1={10}^{-6}molSimilarly,ForpH=8-lo{g}_{10}[H^{+}]=8\Rightarrow [H^{+}{]}_{2^{nd}Solution}={10}^{-8}mol{L}^{-1}Numberof{H}^{+}ionsin1Lsolution={10}^{-8}\times 1={10}^{-8}molTotalvolume=(1+1)L=2Ltotal\left(H^{+}\right)ion=(H^{+}{)}_{1^{st}solution}+(H^{+}{)}_{2^{nd}Solution}={10}^{-6}+{10}^{-8}=1.01\times {10}^{-6}molConcentrationof\left[H^{+}\right]=\frac{(H^{+}{)}_{total}}{TotalVolume}=\frac{1.01\times {10}^{-6}}{2}=5.05\times {10}^{-7}p{H}_{final}=-lo{g}_{10}(5.05\times {10}^{-7})=6.29$