Chloroacetic acid has a relatively large equilibrium constant, so at low acid concentrations it is necessary to use the quadratic equation in order to calculate the concentrations of the aqueous species. Ka for ClCH2COOH is 1.4 ´ 10-3. For the problems that follow, consider one liter of a solution that originally had 0.0200 mol of chloroacetic acid.


What is the equilibrium concentration of [ClCH2COOH]?

a. 0.010

b. 0.012

c. 0.015

d. 0.017

3 answers

ClCH2COOH ==> ClCH2COO^- + H^+

Ka = (H^+)(ClCH2COO^-)/((ClCH2COOH)
(H^+)=x
(ClCH2COO^-)=x
(ClCH2COOH) = 0.02-x
a. 0.010
The answer is C).015

Find x through the quadratic equation x^2^ +(1.4E-3)x - (2.8E-5)=0