Results
Uncertainty = ±0.05cm3
Explanation of results and observations
In trial 1, 13cm3 of oxalic acid titrated the solution of sodium hydroxide and phenolphthalein indicator. The solution turned from dark pink, to light pink and then colourless. It turned colourless because the acid had neutralized the solution and it was now neutral.
The same happened in trial 2 as the solution also turned colourless because it was neutralized.
In the third trial the solution was not neutralized. Instead the oxalic acid and the sodium hydroxide reached equilibrium where the concentration of each was equal. Therefore the colour was a very light, almost clear, pink.
Equation for the reaction
(COOH)2(aq) + 2NaOH(aq) (COONa)2(aq) + 2H2O(l)
Concentration = amount of solute
Volume in dm3
Volume = 12.2 / 1000 = 0.0122dm3
Moles = 25 / 1000 = 0.025*2 = 0.05
Concentration = 0.05 / 0.0122
= 4.09M
= 4M
Uncertainties
Balance = 0.001/ 1.50 * 100 = 0.06%
Burette = 0.5/25.0 *100 = 2%
Pipette = 0.04/ 25.0 *100 = 0.16%
Volumetric flask = 0.50/250*100 = 0.20%
Total uncertainty = 0.06% + 2% + 0.16% + 0.20% = 2.42%
Therefore concentration of sodium hydroxide = 4 ± 2.42% = 4 ± 2
Conclusion and evaluation
The concentration of the given Sodium Hydroxide solution is 4M.
This value is calculated from finding the amount (number of moles) in the solute (NaOH). This is calculated through the mole ratio which in this case was 1:2, and dividing it by the volume of oxalic acid used in dm3.
Weaknesses and limitations
Too much phenolphthalein indicator may have been put into the solution. This would cause an imbalance in the solution and more acid would be required to neutralize the solution.
The percentage error lies outside the uncertainties of the experiment. This means that the results obtained were not very accurate and are therefore not reliable. These uncertainties may have been brought about by the apparatus used.
The apparatus may have been contaminated due to having not been sterilized beforehand, which would bring about an error.
The measurements taken may have been incorrect, that is the readings may have been inaccurate due to the eye position.
The indicator changed colour in between 11 and 12 cm3. However if the burette tap was left open for longer the solution would be clear but it would be more acidic than neutral.
The balance was very sensitive to the environment; this could have increased the uncertainty of the experiment.
Improvements
Ensure that all the equipment is thoroughly cleaned / sterilized before use. This reduces the amount of uncertainties and ensures that the solutions are clean and not contaminated.
Repeat the experiment several times so as to reduce the amount of errors and uncertainties.
Read measurements correctly, keeping the eye at the correct level that would enable accurate results.
Ensure that all the apparatus function correctly before beginning the experiment.
Place the balance in a room where minor factors would not affect it.
Use more accurate apparatus so as to decrease percentage errors.
