Question

In the saponification of methyl salicylate, how does equilibrium of the reaction affect yield

Answer 1

The esterification reaction is reversible, reactants are in equilibrium with products: When the reaction reaches equilibrium there is still a large amount of reactants left in the mixture resulting in a poor yield of the ester.

The yield of ester can be improved by increasing the concentration of one of the reactants (either the alcohol or the carboxylic acid).
By Le Chatelier's Principle an excess of one reactant will drive the reaction to the right, increasing the production of ester, and therefore increasing the yield of ester.
In our experiment we are using an excess of carboxylic aicd (acetic acid which is also known as ethanoic acid).

From the balanced chemical equation, you will also appreciate that the presence of water in the reaction mixture will drive the equilibrium to the left, favouring the formation of reactants rather than ester.
So, another way to improve yield is to remove the water as it forms. Concentrated sulfuric acid can be used for this purpose because it reacts rapidly with water to form a hydrated form of sulfuric acid, effectively removing the water from the reaction mixture^a

The esterification reaction is quite slow.

Heating the reaction mixture will speed up the rate of reaction.
The experimental technique we are using is known as "heating under reflux". As the volatile components in the reaction mixture vaporise, the hot vapours rise up into the condenser. Cool water running around inside the water-jacket around the condenser removes the heat from the hot vapours, cooling them down and allowing them to condense on the inside of the condenser. This cooled liquid runs back down the inside of the condenser and is returned to the reaction mixture.
Heating the reaction mixture under reflux prevents the loss of volatile reactants and products.

Concentrated sulfuric acid is used as a catalyst to speed up the rate at which the ester is formed