Question

The degree of ionisation of a 0·1M bromoacetic acid solution is 0·132. Calculate the pH of the solution and pK_a of bromoacetic acid.

Solution

The concentration of hydrogen ion,

space equals space open square brackets straight H to the power of plus close square brackets space equals space straight C space cross times space straight alpha equals space 0.1 space straight M space cross times space space 0.132 equals space 0.0132 space straight M

Now space pH space equals space minus log space open square brackets straight H to the power of plus close square brackets space space space space space space space space space space space space equals negative log space left parenthesis 0.0132 right parenthesis equals space 1.88 Now space straight K subscript straight a space space equals space fraction numerator Cα squared over denominator 1 minus straight alpha end fraction equals space fraction numerator 0.1 space cross times space left parenthesis 0.132 right parenthesis squared over denominator 1 minus 0.132 end fraction space space space space space space space space space space space space equals space 2.01 space cross times space 10 to the power of negative 13 end exponent therefore space space pK subscript straight a space equals space minus log space straight K subscript straight a space equals space minus log space left parenthesis 2.01 space cross times space 10 to the power of negative 3 end exponent right parenthesis space equals space 2.7

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