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Difficulty: EasypH and pOH Scale and Calculations

An aqueous solution at 25∘C25^\circ\text{C} has a hydroxide ion concentration ([OH−][OH^-]) of 1.0×10−11 mol dm−31.0 \times 10^{-11}\text{ mol dm}^{-3}. What is the pH of this solution?

  1. 3.03.0Answer
  2. B
    11.011.0
  3. C
    7.07.0
  4. D
    1.0×10−111.0 \times 10^{-11}

Answer

The pH of the solution is 3.03.0.
Taking the negative logarithm of the hydroxide ion concentration gives a pOH value of 11.011.0. Subtracting this from 14.014.0 yields a pH of 3.03.0, accurately indicating an acidic solution.

Step-by-Step Solution

1
Calculate the pOH from the hydroxide ion concentration
pOH=−log⁡10(1.0×10−11)=11.0\text{pOH} = -\log_{10}(1.0 \times 10^{-11}) = 11.0
pOH is defined as the negative logarithm to base 10 of the hydroxide ion concentration.
2
Calculate the pH using the water ionic product relationship at 25∘C25^\circ\text{C}
pH=14.0−pOH=14.0−11.0=3.0\text{pH} = 14.0 - \text{pOH} = 14.0 - 11.0 = 3.0
The sum of pH and pOH in aqueous solutions at 25∘C25^\circ\text{C} is equal to 14.0.

Key Concept

Relationship between [OH−][OH^-], pOH, and pH in aqueous solutions
Estimated Time:45s
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Topics

pH and pOH Scale and Calculations

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