Page 182 - Analytical Electrochemistry 2d Ed - Jospeh Wang

EXAMPLES 167

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EXAMPLES

Example 5-1 Calculate the relative error (in proton concentration) that would
occur if the pH of a 1 10 2 M NaOH solution were measured with a pH glass
electrode k H;Na ˆ 10 10 ; assuming activity coef®cient of 1.0).

Solution The concentration of the interfering sodium ion is 1 10 7 2 M, while
that of the target proton is

‰H Šˆ K =‰OH Šˆ 10 14 =10 2 ˆ 1 10 12 M
‡
w
From equation (5.6), we thus obtain

2
E ˆ K ‡ 0:059 log‰1 10 12 ‡ 10 10 1 10 †Š
cell
The relative error in concentration is thus

2
‰10 10 1 10 †=10 12 Š 100 ˆ 100%