A 1.0-L buffer solution is 0.120 M in HNO2 and 0.180 M in NaNO2. A)Determine the concentrations of HNO2 and NaNO2 after addition of 1.7 g HC?

A)
Molar mass of HCl = (1.01 + 35.45) g/mol = 36.46 g/mol
No. of moles of HCl added = (1.7 g) / (34.46 g/mol) = 0.049 mol
Concentration of HCl after dissolving in the solution = (0.049 mol)/ (1 L) = 0.049 M

NaNO₂ + HCl → HNO₂ + NaCl

After addition of 1.7 g HCl :
Concentration of HNO₂ = (0.120 + 0.049) M = 0.169 M
Concentration of NaNO₂ = (0.180 - 0.049) M = 0.131 M


B)
Molar mass of NaOH = (22.99 + 16.00 + 1.01) g/mol = 40.00 g/mol
No. of moles of NaOH added = (1.7 g) / (40.00 g/mol) = 0.043 mol
Concentration of NaOH after dissolving in the solution = (0.043 mol)/ (1 L) = 0.043 M

HNO₂ + NaOH → NaNO₂ + H₂O

After addition of 1.7 g NaOH :
Concentration of HNO₂ = (0.120 - 0.043) M = 0.077 M
Concentration of NaNO₂ = (0.180 + 0.043) M = 0.223 M


C)
Molar mass of HI = (1.0 + 126.9) g/mol = 127.9 g/mol
No. of moles of HI added = (1.7 g) / (127.9 g/mol) = 0.013 mol
Concentration of HI after dissolving in the solution = (0.013 mol)/ (1 L) = 0.013 M

NaNO₂ + HI → HNO₂ + NaI

After addition of 1.7 g HI :
Concentration of HNO₂ = (0.120 + 0.013) M = 0.133 M
Concentration of NaNO₂ = (0.180 - 0.013) M = 0.193 M