Question

Find the pH of a$0.002N$ acetic acid solution if it is 2.3% ionized at a given dilution.

Answer 1

Hint: pH is the negative base 10 logarithm $( - {\log _{10}})$of the hydrogen ion concentration of a solution.
To calculate pH, take the log of given hydrogen ion concentration and reverse the sign.

Complete step by step answer:
Given:
Degree of dissociation of acetic acid = \[\alpha = \dfrac{{2.3}}{{100}} = 0.023\]
 Concentration of acetic acid \[\;C = 0.002M\]
Now,
When acetic acid in the equilibrium
\[
  C{H_3}COOH \rightleftharpoons C{H_3}CO{O^ - } + {H^ + } \\
  C\left( {1 - \alpha } \right)\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;\;C\alpha \;{\text{ }}\;{\text{ }}\;{\text{ }}\;\;{\text{ }}\;{\text{ }}\;{\text{ }}\;{\text{ }}\;C\alpha \\
\]
So,
\[\left[ {{H^ + }} \right] = C\alpha = 0.002 \times 0.023 = 4.6 \times {10^{ - 5}}M\]
Now, pH of acetic acid in solution
\[
  pH = - log\left[ {{H^ + }} \right] \\
  pH = - log\left[ {4.6 \times {{10}^{ - 5}}} \right] \\
  pH = 4.3372 \\
\]

Note:
-The term pH is an abbreviation for the potential of hydrogen.
-The pH scale describes the acidity of the solution: acidic, neutral, or basic.
-In labs pH can be determined by a pH indicator such as pH paper.