Data collection:
Data Processing:
Average of volume of HCl titrated = [Volume of HCl titrated [mL] (±0.1 mL) in 2nd trial + Volume of HCl titrated [mL] (±0.1 mL) in 3rd trial] / 2
No of mol of HCl titrated = Concentration of HCl * Average volume of HCl titrated
No of mol of NaOH = No of mol of HCl titrated
Concentration of NaOH = No of mol of NaOH / volume of NaOH
Evaluation of Experimental Procedure:
The estimated systematic error could occur when I did the 1st experiment, as the result was not close to the other two results. This is related to the rapid titration that I did to find the rough estimate. The result became not accurate.
The main concern is the used of secondary standard. HCl has small Mr, therefore in calculation process; the percentage of error would be larger. It means that the error could increase. I could decrease the error by using primary standard, which are KHP or Na2O3 . They have relatively high molar mass, that can reduce the percentage of error in calculation. They are also stable as both the solid and in the solution, that can reduce the error in experiment.
The other possible error could be because of the amount of indicator. I added the phenolphthalein by using dropper. However, the amount of phenolphthalein added to the 1st, 2nd and 3rd experiments may be different, as 1 drop was not exact enough. It would be better if I used small pipette ( 1 mL pipette ) to add the phenolphthalein to the NaOH solutions, therefore the indicator would show the colour change more accurately.
Another source of error could be because of the indicator. As we know, that I was supposed to stop the titration when the solution turned colorless. However, the decision of when is the solution colorless enough is relative and subjective. Because everybody has their own opinion whether the solution is colorless enough or not. Perhaps I made a wrong decision when I stopped the titration – whether it was too early or too late – therefore it would be better if I used digital pH meter. I could stop the titration when the digital pH meter showed that the pH was 7 – which is neutral- and it would decrease the error. Moreover, digital pH meter has an exact uncertainty; therefore the result would be even more accurate.
From my experience in the 1st titration, I should shake the NaOH solution gently when I was doing titration. It made the solution mixed quickly, and it would reduce the error.
I think another sources of error were small, as the apparatus used to measure the solutions have relatively small uncertainties such as burette (0.05 mL) and pipette (0.1 mL), and I followed the rest of the procedure correctly.
Conclusion:
The concentration of the NaOH solution used in this experiment is approximately 0.0366 ±2% mol dm-3.
