Question

Calculate $\left[CH{Cl}_{2}CO{O}^{-}\right]$ in a solution that is $0.01M$ in $HCl$ and $0.01M$ in $CH{Cl}_{2}COOH$.

Take $(K_a=2.55\times {10}^{-2})$

• A. $\left[CH{Cl}_{2}CO{O}^{-}\right]=6.126\times {10}^{-3}M$
• B. $\left[CH{Cl}_{2}CO{O}^{-}\right]=6.126\times {10}^{-5}M$
• C. $\left[CH{Cl}_{2}CO{O}^{-}\right]=6.126\times {10}^{-1}M$
• D. $\left[CH{Cl}_{2}CO{O}^{-}\right]=6.126\times {10}^{-7}M$

Answer 1

Answer: (A)

$\left[CH{Cl}_{2}CO{O}^{-}\right]=6.126\times {10}^{-3}M$

$CH{Cl}_{2}COOH⟶H^{+}+CH{Cl}_{2}COO{O}^{-}$
$0.01-x$ $0.01+x$ $x$
$\frac{x(0.01+x)}{0.01-x}=2.55\times {10}^{-2}$
$0.01x+x^2=2.55\times {10}^{-4}-2.55\times {10}^{-2}x$
$x^2+0.355x-0.000255=0$
$x=\frac{-0.0355\pm \sqrt{0.04775}}{2}=1.1\times {10}^{-2}$
$CH{Cl}_{2}CO{O}^{-}=6.126\times {10}^{-2}$