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Difficulty: MediumpH and pOH Scale and Calculations

Complete the statement below by calculating the missing pOH and pH values for the given alkaline solution.

Answer:A solution of potassium hydroxide (KOH\text{KOH}) has a hydroxide ion concentration of 0.01 mol dm−30.01\text{ mol dm}^{-3} at 25∘C25^\circ\text{C}. The pOH of this solution is 【2】 and its pH is 【12】.

Answer

The pOH of the potassium hydroxide solution is 2 and its pH is 12.
Potassium hydroxide (KOH\text{KOH}) dissociates completely in water to yield a hydroxide ion concentration of [OH−]=1.0×10−2 mol dm−3[\text{OH}^-] = 1.0 \times 10^{-2}\text{ mol dm}^{-3}. The pOH is calculated as −log⁡10(10−2)=2-\log_{10}(10^{-2}) = 2. Since pH+pOH=14\text{pH} + \text{pOH} = 14 at 25∘C25^\circ\text{C}, subtracting 2 from 14 gives a pH of 12.

Step-by-Step Solution

1
Calculate the pOH from the given hydroxide ion concentration [OH−][\text{OH}^-].
pOH=−log⁡10(0.01)=−log⁡10(10−2)=2\text{pOH} = -\log_{10}(0.01) = -\log_{10}(10^{-2}) = 2
KOH\text{KOH} is a strong monobasic base that fully dissociates in water, giving [OH−]=0.01 mol dm−3[\text{OH}^-] = 0.01\text{ mol dm}^{-3}.
2
Calculate the pH using the relationship pH+pOH=14\text{pH} + \text{pOH} = 14 at 25∘C25^\circ\text{C}.
pH=14−pOH=14−2=12\text{pH} = 14 - \text{pOH} = 14 - 2 = 12
The sum of pH and pOH for any aqueous solution at standard temperature (25∘C25^\circ\text{C}) equals 14.

Key Concept

Determination of pOH and pH for strong base solutions using the ion product constant of water.
Estimated Time:1m 0s
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Topics

pH and pOH Scale and Calculations

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