Buffers And Acid-Base Titrations

 

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

      pH = 2.90                         Ka(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

 

      Ka = [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