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JAMB Chemistry 2018 Paper

Question : 58

Total: 87

^{-11}

^{-3}

^{OH}

? [log102 = 0.3010]

Solution:

Concept:

The pH of a solution is found from its hydrogen ion concentration, and pH plus pOH always equals 14 at 25°C.

Explanation:

First, calculate the pH using the formula:

\mathrm{pH} = -\log[\mathrm{H}^+]

Given

[\mathrm{H}^+] = 2.0 \times 10^{-11}\ \mathrm{mol\ dm^{-3}}

\mathrm{pH} = -\log(2.0 \times 10^{-11})

\mathrm{pH} = -(\log 2.0 + \log 10^{-11})

\mathrm{pH} = -(0.3010 - 11) = 10.699 \approx 10.70

Now use the relationship:

\mathrm{pH} + \mathrm{pOH} = 14

\mathrm{pOH} = 14 - 10.70 = 3.30

Answer:

A. 3.30

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