no of moles of benzoic acid = W/G.M.Wt
                                             Â
= 0.235/122 = 0.001924 moles
  no of moles of NaOH  = molarity * volume
in L
        Â
0.001924Â Â Â Â Â Â Â Â Â Â Â Â Â
= 0.128* volume in L
volume in
LÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
= 0.001924/0.128 = 0.015L
total
volume                  Â
= 0.015 + 0.3 = 0.315L
molarity of C6H5COO-Â Â = no of moles/volume
                                     Â
= 0.001924/0.315Â Â = 0.0061 M
      C6H5COO- + H2O
---------> C6H5COOH + OH-
                Â
kb  = x*x/0.0061-x
                Â
1.63*10-10Â Â = x2/0.0061-x
                Â
1.63*10-10*(0.0061-x)Â Â = x2
                             Â
x = 9.97*10-7
             Â
[OH-] = x = 9.97*10-7 M
             Â
[C6H5COO-] = 0.0061-0.000000997 = 0.00609M
              Â
[H3O+] = Kw/[OH-]
                             Â
= 1*10-14/9.97*10-7Â Â = 1*10-7
M
                 Â
[Na+]Â Â = 0.0061M