Determine the concentration of the unknown ethanoic acid solution by titrating with a known concentration of sodium hydroxide
Equipment and Materials
* Unknown ethanoic acid
* 50cm3 burette
* 250cm3 Erlenmeyer flask
* 100cm3 beaker (for CH3COOH)
* 200cm3 beaker (for NaOH)
* 100cm3 beaker (for waste)
* Standardized sodium hydroxide solution
* Burette clamp
* Retort stand
* Phenolphthalein indicator
* 50cm3 graduated cylinder
* Distilled water (to rinse the flask)
To begin with, obtain approximately 200 cm3 of sodium hydroxide solution. Then, set up the retort stand and burette clamp as indicated in the diagram below. Using two 10 cm3 aliquots of the NaOH solution, rinse the burette twice. Next, fill to above the 0.00cm3 mark and drain down to below the 0.00cm3 mark in order to remove any air bubbles. After that, transfer 50 cm3 of the unknown acid into the 250cm3 flask. Into the same flask, place 2 drops of the phenolphthalein indicator. Finally, add sodium hydroxide from the burette until you reach the endpoint.
To accommodate for the sodium hydroxide that splashes to the sides of the flask, distilled water was used. Using the distilled water on the sides of the flask was rinsed down to bring the sodium hydroxide to the rest of the solution in the flask. Also, when dropping a half-drop into the flask, the following procedure was used: First, a half-drop was made at the tip of the burette. Then, using the flask, the half-drop was collected to the flask’s side. Finally, using the distilled water, the half-drop was rinsed down to the rest of the solution.
To make it easier to recognize the endpoint of the reaction, a white paper was put under the flask. This way, it was easier to see when the solution changed color.
Observation (Data Collection):
Measurements Recorded During the Experiment
Initial Burette Reading (ml?0.02ml)
Final Burette Reading (ml?0.02ml)
Volume of Ethanoic Acid Used (ml?0.04ml)
*To increase the results, trial 3 and 4 was taken from another group to get more data, thereby increasing the accuracy of the data.
Descriptions of the Substances Used and Produced
Clear solution, low viscosity, slippery
Clear solution, acidic,
Clear solution, comes in bottle, add as drops
Solution Produced (NaCH3COO(aq) + H2O)
Clear/pink throughout, trail 4 was the most successful as it was closest to clear than all other trails. Volume of trial 1 was greatest as a lot of water was used in order to wash down the sodium hydroxide stuck to the side of the flask.
The neutralization reaction between sodium hydroxide and ethanoic acid is
Sodium Hydroxide + Ethanoic acid –> Sodium Ehthanoate + Water
Therefore, the molar ratio is 1 mole of sodium hydroxide to 1 mole of ethanoic acid. Sodium hydroxide is known to have a concentration of 1.003 mol dm-3ï¿½0.004 mol dm-3.
Consequently, the following represents the calculations to determine the concentration of ethanoic acid in trial 1:
Using similar calculations, the concentration of ethanoic acid for trials 2,3, and 4 were calculated as well. The following table represents the results.
Results for the calculations of the concentration of ethanoic acid used in each trial
Concentration of CH3COOH / mol dm-3 CH3COOH
Uncertainties / %
In conclusion, the result of this lab indicates that the concentration of CH3COOH is 0.910 mol dm-3. Using this value, and the actual value of ethnoic acid, 0.9190 mol dm-3 ï¿½0.0004 mol dm-3, percent error was calculated as follows:
With this, we see that the percent of uncertainties is greater than the percent error. The percent of uncertainties represents the random errors, in which the measured value can either be bigger or smaller than the accepted value, due to an imprecise measurement. To improve these random errors, it is necessary to use more precise equipment and/or repeat measurements. One example of this would be to use a pipette instead of a graduated cylinder, especially because ?0.4 cm3 is a relatively large uncertainty. Consequently, the use of such equipment led to the percent of uncertainties being greater than the percent error. This means that the random errors cover for the errors in this lab. However, there are a couple potential systematic errors that should be appointed in this lab. The biggest one would be that it is hard to get to the endpoint, where the solution is barely pink. In all trials, the solution became clear pink.
However, it was only in trial 4 that the solution was truly ambiguous to whether it was slightly pink. The difficulty of getting to this ambiguous clear pink is definitely a systematic error as it always leads to a larger volume of sodium hydroxide used to react. One way to improve this may be to perform the lab in a longer time span. When I performed the lab, I felt pressured to get a sufficient amount of trials done within the class period. By stretching the time span of the lab, it may be possible to take more time and get better quality results. A more realistic improvement may be to record measurements more frequently when approaching the endpoint. This would give us two measurements that the endpoint lies within, helping us estimate where the endpoint actually is.
However, improving this error would lead to a smaller volume of sodium hydroxide, a smaller value for the concentration of ethanoic acid, which would make the observed value further from the true value. Another systematic error in this lab is the sodium hydroxide splashing to the sides of the flask. Although using water to rinse the sodium hydroxide down was aimed to cover this, another way to improve this may be to use equipment with a wider mouth, such as a beaker, instead of a flask. Once again, improving this error would lead to a greater percent error for the same reasons as the difficulty of getting an ambiguous pink color.
Next, although it most likely did not affect the results in this lab, there is a question to whether rinsing the burette two times is sufficient. To improve this, it may be suggested that rinsing the burette 4 times is more sensible, even though it is time consuming. A final systematic error comes when transferring the ethanoic acid from the graduated cylinder. When this happens, some of the ethanoic acid may be retained in the graduated cylinder. This is a systematic error as this always leads to a smaller volume of ethanoic acid than measured. To improve this error, one may pour a tiny bit more than 50 ml of ethanoic acid, and measure that as 50 ml of ethanoic acid. Improving this error leads to a larger volume of ethanoic acid, a lower concentration of ethanoic acid, and once again, an increase in percent error.
All in all, it is very interesting how knowing the amount of one substance can help determine the amount of another substance, although it is a topic that appears frequently in chemistry. In this case, knowing the number of moles of sodium hydroxide enabled us to know the concentration of the ethanoic acid. Furthermore, this lab helps one enhance their knowledge on the difficulty of setting up a lab. By reviewing and understanding the errors to a lab, one can relate the improvements to future labs. In a nutshell, this lab exemplified the process of titration, and how useful it can be.