To prepare soap, a student refluxed 8.9 g of glyceryl tristearate (obtained from animal fat), 2 g of sodium hydroxide pellets and 30 cm³ of ethanol, together with a few anti-bumping granules, using the apparatus shown on the right - Leaving Cert Chemistry - Question 2 - 2010

The reaction mixture was heated under reflux to bring the reaction to completion and to allow sufficient time for the reaction to occur, providing the necessary energy for the reaction to happen without loss of ethanol or volatile materials.

During the reflux, the glyceryl tristearate reacts with sodium hydroxide and ethanol to undergo hydrolysis, resulting in the formation of sodium stearate and glycerol.

The purpose of the ethanol in the reaction is to act as a solvent that helps in dissolving the reactants and promoting the hydrolysis reaction.

A diagram should show a distillation setup with a condenser where the ethanol vaporizes during heating and is then condensed back to a liquid, which can be collected separately.

The soap (sodium stearate) was isolated from the reaction mixture by adding the mixture to brine (saturated sodium chloride solution), which precipitates the soap out. The precipitated soap is then collected by filtration.

After isolation, the soap was purified by washing it with brine and water to remove any impurities, ensuring that excess reactants and by-products were washed away.

To calculate the percentage yield, first determine the theoretical yield of sodium stearate based on the amount of glyceryl tristearate used. Then use the actual yield (7.0 g) to calculate:

Percentage Yield = (Actual Yield / Theoretical Yield) × 100 Using the provided calculations in the marking scheme: For 8.9 g glyceryl tristearate, the yield of soap is calculated to be between 76 - 77%.