Buffers And Acid-Base Titrations

18) m = ? g NaC₃H₅O₃          [HC₃H₅O₃] = 0.150 M          V = 1.00 L

      pH = 2.90                         K_a(HC₃H₅O₃) = 1.4 x 10^-4

      NaC₃H₅O₃ (aq) Na⁺(aq) + C₃H₅O₃^-(aq)

      [H⁺] = 10^-pH = 10^-2.90 = 1.3 x 10^-3 M

                 HC₃H₅O₃(aq)             H⁺(aq)        +       C₃H₅O₃^-(aq)

      [ ]_i          0.150                                  0                               x

      [ ]_c        -1.3 x 10^-3                    +1.3 x 10^-3               +1.3 x 10^-3     

      [ ]_e        0.150-1.3 x 10^-3                 1.3 x 10^-3                x+1.3 x 10^-3

      K_a = [H⁺] x [C₃H₅O₃^-]/[HC₃H₅O₃]

      1.4 x 10^-4 = 1.3 x 10^-3 • (x + 1.3 x 10^-3)/(0.150 - 1.3 x 10^-3) ≈ 1.3 x 10^-3 • x/0.150

      [C₃H₅O₃^-] = 0.016 M

      [NaC₃H₅O₃] = n/V = 0.016 mol C₃H₅O₃^-/L x 1 mol NaC₃H₅O₃/1 mol C₃H₅O₃^- = 0.016 M

      m = 0.016 mol NaC₃H₅O₃ x 112.07 g NaC₃H₅O₃/1 mol NaC₃H₅O₃

      m = 1.8 g NaC₃H₅O₃