Calculate the pH (nearest integer) of a solution containing 1.8gNaHSO4 per 100mL. Ka for HSO−4⇌H++SO−4 is 1.26×10−2.
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Solution
The molar mass of sodium bisulphate is 120 g/mol. The molarity of sodium bisulphate is 1.8120×0.1=0.15M.
HSO−4
H+
SO2−4
Initial molarity (M)
0.15
0
0
Equilibrium molarity (M)
0.15-x
x
x
The expression for the acid dissociation constant Ka is Ka=[H+][SO2−4][HSO−4] Substitute values in the above equation. x×x0.15−x=1.26×10−2 x=[H+]=0.0436 pH=−log[H+]=−log0.0436=1.36.