Standardization of sodium hydroxide solution using oxalic acid.

Qualitative data :

The colour indicator (phenolphthalein) in the NaOH solution changes from pink to colourless. The oxalic acid used to counterbalance the NaOH solution did not change a lot from its theoretical volume which is + 27cm³.

Data processing :

Gross volume of H2C2O4.2H2O used with uncertainty :

29.60 + 29.00 + 27.50   =   28.7 cm³ + 0.1 cm³.

                 3

Uncertainty : | 28.7-29.6 | + | 28.7-29.0 | + | 28.7-27.5 |   x 100  =  8.4 %  

                                           28.7

Gross volume of H2C2O4.2H2O used with percentage of  uncertainty = 28.7 cm³ + 8.4% cm³.

Chemical equation : H2C2O4+ 2NaOH  → Na2C2O4 + 2H2O

The number of moles of H2C2O4.2H2O :

= Mass of H2C2O4.2H2O (g)

   Relative Molecular Mass

= 1.6253 g

   126g/mol

= 0.0129 mol.

Uncertainty : 0.0001 x 0.0129

                       1.6253

                    = 7.937 x 10-7 mol.

So the number of moles of H2C2O4.2H2O with uncertainty = 0.0129 + 7.937 x 10-7 mol.

The concentration of H2C2O4.2H2O :

= Number of moles

      Volume (dm³)

= 0.0129 mol

      0.25 dm³

= 0.0516 mol/dm³.

Uncertainty : ( 0.00025 + 7.937 x 10-7 mol  ) (0.0516)

1.              0.0129 mol

         = 5.47748 x 10-5 mol/dm³.

So the concentration of H2C2O4.2H2O with uncertainty =  0.0516 + 5.47748 x 10-5  mol/dm³.

The concentration of diluted NaOH used :

MaVa = a

MbVb     b

Mb       = 2 (0.0516 mol/dm³)(0.0287dm³)

                               (1)(0.025dm³)

          = 0.1185 M.

Conclusion :

The concentration of NaOH that was used during titration method is 0.1185 M.