Hydrolysis of an Ester

Abstract

 The objective of this lab is the hydrolysis of an unknown ester using a carboxylic acid and an alcohol while using a catalyst. Method performed during this lab is using the hickman distillation apparatus, recrystallization, and taking melting points. It was determined the unknown ester was salicylic acid with an MP of 157-164 °C (standard MP is 156°C) The weight of product recovered was 0.751g with a percent yield of 82.8%. The lab was conducted by placing 10ml of water in a 50ml round bottom flask, while the hickman apparatus was assembled. 2.0g of sodium hydroxide and 1.0g of the unknown ester was added to the round bottom flask and swirled until it dissolved. It was then placed over the heating mantle at a set temp of 95°C. Once the liquid began to drip it was refluxed for 30 minutes, it was then cooled and transferred to a 100ml beaker. Carefully under the hood 8ml of hydrochloric acid was added to make the solution acidic, cooled again and the solid was collected via suction filtration. The product was recrystallized by placing it in a 125ml Erlenmeyer flask, 20ml of distilled water was also in the flask. It was then placed top of a hot plate until it boiled, when fully dissolved and cooled it was again suction filtered. Product was already dried enough, so it was mixed with salicylic acid (Mp of 156°C) and benzoic acid (MP of 122°C). While taking the melting points one had a wide range of 119.6-157.2 °C and the second melting point had a narrow range of 157-164°C.  It was determined that our unknown acid was salicylic acid due to the narrow range this the unknownester being methyl salicylate. [pic 1]

Results

Final weight of product: 0.751g

Melting points obtained with mixed products

Mp 119.6-157.2 °C

Mp 157-164 °C

Finding percent yield

    = to mol of product[pic 2]

Salicylic Fwt = 138.121g/mol

138.121g/mol x 0.00657mol = 0.907g

[pic 3]

Conclusion

All objectives of the lab were successfully obtained and it was determined that the unknown acid was salicylic acid and the unknown ester to be methyl salicylate. Since the melting point with the narrow range was 157-164 °C (Salicylic acid has an Mp of 157°C). The percent yield was 82.8% with a final product weight of 0.751g there is a low chance to get 100 percent yield since side products could remain in the product. There’s always possible error when transferring products to other objects, and there could have been an excess of HCL or refluxing wasn’t done enough or done correctly.

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