Answer to Question #135000 in General Chemistry for hi

Question

A buffer solution is 0.20M in acetic acid and in sodium acetate. Calculate the change in pH up on adding 1.0ml of 0.10M HCl acid to 10 ml of this solution. ?

Answer 1

The ICE approach for the equilibrium yields;

$CHCO_2H+H_2O \leftrightharpoons H_3O^{+}+CH_3CO_2^-$

The initial concentration of $CH_3CO_2H$ $=0.20$

Change $=x$

Equilibrium concentration$= 0.20-x$

The initial concentration of $CH_3CO_2^-$

.$=0.20$

Change$=x$

Equilibrium concentration$= 0.20+x$

Substituting the equilibrium concentration terms into the $K_a$ expression, assuming $x\lll$ $0.20$ and solving the simplified equation for $x$ yields

$x= 1.8\times 10^{-5}$

$[H_3O^+]=0+x=1.8\times 10^{-5}$ $pH=-log [H_3O^+]=-log (1.8\times 10^{-5}M)=4.74$