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)
- 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.
by
juji (student)
