Question

A 1.0-L buffer solution is 0.125 M in HNO2 and 0.190 M in NaNO2.

a) Determine the concentrations of HNO2 and NaNO2 after addition of 1.9 g HCl.

b) Determine the concentrations of HNO2 and NaNO2 after addition of 1.9 g NaOH.

c) Determine the concentrations of HNO2 and NaNO2 after addition of 1.9 g HI

Answer 1

A 1.0 L buffer of 0.125 M HNO2 (weak acid) and 0.190 M NaNO2 (conjugate base of wek acid)

a) after HCl = 1.9 g/36.5 g/mol = 0.052 mol was added

new concentration [HNO2] = (0.125 M x 1 L + 0.052 mol)/1 L = 0.177 M

new concentration [NaNO2] = (0.190 M x 1 L - 0.052 mol)/1 L = 0.138 M

b) after NaOH = 1.9 g/40 g/mol = 0.0475 mol was added

new concentration [HNO2] = (0.125 M x 1 L - 0.0475 mol)/1 L = 0.0775 M

new concentration [NaNO2] = (0.190 M x 1 L + 0.0475 mol)/1 L = 0.2375 M

c) after Hl = 1.9 g/127.911 g/mol = 0.015 mol was added

new concentration [HNO2] = (0.125 M x 1 L + 0.015 mol)/1 L = 0.140 M

new concentration [NaNO2] = (0.190 M x 1 L - 0.015 mol)/1 L = 0.175 M