Preparing benzoic acid from benzylalcohol

By adding sodium carbonate, we will now test whether what obtained is benzoic acid or not, because one can observe bobbles if it is an acid. After that we burn it to test if it is aromatic. Soot would be possible to obtain if it was to be aromatic.

Data Collection

Mass of benzylalcohol

3.991 grams

Mass of flask (before adding benzoic acid)

95.47 grams

Mass of flask (after adding benzoic acid)

96.68 grams

After the addition of sodium carbonate

Bubbles were obtained

After burning it

Soot was obtained

Data Processing

Mass of benzoic acid

96.68 - 95.47 = 1.21 grams

We assume that the reaction goes to completion which would mean that one mole of benzylalcohol should give one mole of benzoic acid.

Hence, the theoretical yield is 100% by amount of mol.

Molar mass

Benzylalcohol

08 g/mol

Benzoic acid

22 g/mol

Initial amount of benzylalcohol:

Amount of benzoic acid at completion:

Percentage yield:

Conclusion

The actual yield was about 27%. That means the underestimated processes of purification such as stated in the hypothesis. The amount of the produced benzoic acid in this experiment was probably higher than the amount we have obtained in the end, because the number of impurities in the final product were eminently lower than the amount of lost benzoic acid due to purification processes.

After all, it is quite certain that the final product was benzoic acid based on the fact that, according to tests, it was aromatic and acidic.

Evaluation

Several processes, such as filtering for impurities not soluble in water as well as filtering for impurities soluble in water, were necessary to make sure that the final product of this reaction was as pure as possible. However, it is very likely that at least some of the benzoic acid was lost during that kind of processes, because the product had to be transfered between several containers, and different filters were used. We definitely lost some of the benzoic acid when we filtered out the soluble impurities, because the acid is soluble as it gave of its proton. Even though, the addition of HCl shifted the equilibrium towards the side where the benzoic acid is undissociated, we could not keep all the acid.

We lost a big amount of benzoic acid during the liquid filtering, where it was dissolved to filter out the insoluble impurities. An obvious amount was left in the filter after the dissolved benzoic acid was precipitated due to the cooling of the solution on the funnel.

It is reasonable to assume that the obtained benzoic acid was quite pure, so that impurities were just a small part of the mass of the final product.

Suggestions of improvement:

- increase the number of purification processes to reduce the amount of impurities, even though, that might result in a lower percentage yield do to the fact that some of the benzoic acid might be lost in processes, such as filtering

- when the acid runs through the filter, to filter out impurities, the filter and the funnel should be warm and the solution heated more to make sure that neither the acid precipitates nor is filtered out --> higher percentage yield

- prevent unintentional cooling and precipitation of the acid by being faster with filtering out impurities --> higher percentage yield