Question 1: Define an ester and describe its general molecular structure.

Answer: An ester is an organic compound derived from a carboxylic acid and an alcohol, characterised by the presence of a carbonyl group (C=O) adjacent to an oxygen atom bonded to a carbon chain, with the general structure R–CO–O–R'.

Question 2: Explain the process of esterification using a carboxylic acid and an alcohol.

Answer: Esterification involves the reaction of a carboxylic acid with an alcohol in the presence of a catalyst, usually sulphuric acid, to produce an ester and water. The reaction is reversible and typically requires heating under reflux to proceed efficiently.

Question 1: Describe the main steps involved in the acid-catalysed hydrolysis of an ester.

Answer: The hydrolysis involves protonation of the ester carbonyl oxygen, nucleophilic attack by water, formation of a tetrahedral intermediate, and subsequent breakdown to produce a carboxylic acid and an alcohol, facilitated by acid catalysis.

Question 2: Identify the main reagents and conditions required for converting a carboxylic acid and an alcohol into an ester.

Answer: Reagents include a carboxylic acid, an alcohol, and a catalyst such as concentrated sulphuric acid, with heating under reflux.

Question 1: Calculate the mass of ethanol required to react completely with 0.5 mol of acetic acid to produce 0.5 mol of ethyl acetate. (Molar mass of ethanol = 46 g/mol, acetic acid = 60 g/mol, ethyl acetate = 88 g/mol).

Answer: Mass of ethanol = moles × molar mass = 0.5 mol × 46 g/mol = 23 g.

Question 2: If 10 grams of ethyl acetate are hydrolysed, how many grams of ethanol and acetic acid are produced? (Molar masses as above).

Answer: Moles of ethyl acetate = 10 g / 88 g/mol ≈ 0.1136 mol. Ethanol and acetic acid produced = 0.1136 mol × 46 g/mol ≈ 5.23 g each.

Question 1: List three safety precautions that should be observed when carrying out esterification reactions in the laboratory.

Answer: Use of safety goggles, working in a well-ventilated fume cupboard, and handling concentrated sulphuric acid with care.

Question 2: Describe a simple experimental setup to synthesise ethyl acetate from ethanol and acetic acid, including the key variables to control.

Answer: The setup involves mixing ethanol and acetic acid in a flask with a few drops of concentrated sulphuric acid as a catalyst, then heating under reflux. Variables to control include temperature, molar ratios, and reaction time to optimise yield.

Question 1: A sample of ester reacts with water and produces 12 grams of acetic acid and 8 grams of ethanol. What is the initial mass of the ester used, assuming complete hydrolysis?

Answer: Total mass of ester = 12 g + 8 g = 20 g.

Question 2: Identify at least two industrial applications of esters and explain their importance.

Answer: Esters are used as flavourings and fragrances in the food and cosmetic industries, and as plasticisers in the production of flexible plastics, due to their pleasant smells and chemical properties.

Question 1: Describe the process of synthesising an ester from a carboxylic acid and an alcohol, including the conditions necessary for high yield. Explain how the hydrolysis of the ester can be carried out and its industrial significance.

Answer: Ester synthesis involves reacting a carboxylic acid with an alcohol in the presence of a catalyst such as concentrated sulphuric acid, under reflux to promote the reaction. Conditions like temperature, molar ratios, and catalyst amount influence yield. Ester hydrolysis reverses the process, breaking the ester back into the acid and alcohol, often using water with acid or base catalyst. Industrially, this process is vital for producing fragrances, flavours, and biodegradable plastics.