Formic acid (HCHO ) has

CHEMISTRY · Single correct · A Level · Chemistry · Acids and bases · Acids and bases

Problem

Formic acid (HCHO

_2

) has

K_a = 1.8\times10^{-4}

. For a 0.0020 M solution, a student first estimates

[\text{H}^+]

using

[\text{H}^+] = \sqrt{K_a C_0}

, then solves the exact quadratic expression to obtain the true

[\text{H}^+]

. What is the percent error introduced by the estimate? (a) 14 \% (b) 35 \% (c) 16 \% (d) 8.0 \%