Question 1: Define a carboxylic acid and give an example.

Answer: A carboxylic acid is an organic compound containing a carboxyl functional group (-COOH). Example: Ethanoic acid.

Question 2: Describe the mechanism by which carboxylic acids react with alcohols to form esters.

Answer: Carboxylic acids react with alcohols in the presence of an acid catalyst (like H₂SO₄) to undergo esterification, where the carboxyl group reacts with the alcohol to form an ester and water.

Question 3: Explain why carboxylic acids are considered weak acids.

Answer: Because they do not fully ionise in solution; only a small proportion of their molecules release H⁺ ions, resulting in a weak acidic solution.

Question 1: Calculate the number of moles of ethanoic acid (molecular formula C₂H₄O₂) in 60 cm³ of a 0.5 mol/dm³ solution.

Answer: Number of moles = concentration (mol/dm³) × volume (dm³) = 0.5 × 0.060 = 0.03 mol

Question 2: A student adds 25 cm³ of a 0.1 mol/dm³ solution of a carboxylic acid to an excess of sodium hydroxide. How many moles of sodium hydroxide are required to neutralise the acid?

Answer: Moles of acid = 0.1 × 0.025 = 0.0025 mol; Since acid and base react in a 1:1 ratio, 0.0025 mol of NaOH are required.

Question 1: Describe a safe method to prepare ethanoic acid from ethanol using oxidation. Include safety precautions.

Answer: Oxidise ethanol using potassium dichromate (VI) solution under a fume cupboard, wearing eye protection and gloves. Heat gently with a reflux condenser to prevent vapour escape. Ensure proper disposal of waste chemicals.

Question 2: Identify the variables that must be controlled when testing the acidity of a carboxylic acid solution.

Answer: Variables include temperature, concentration of the acid, and the type of indicator used.

Question 1: A solution of a carboxylic acid has a pH of 2.5. Describe what this indicates about the strength and concentration of the acid.

Answer: A pH of 2.5 indicates the solution is acidic, but not fully ionised, consistent with a weak acid. The relatively low pH suggests a moderate to high concentration of the acid.

Question 2: In an experiment, the volume of carbon dioxide released from a carboxylic acid reacting with a carbonate is measured. Explain what the volume of CO₂ indicates about the reaction's completeness.

Answer: The volume of CO₂ released reflects the extent of the reaction; a higher volume indicates more complete reaction and greater acid concentration.

Question 1: Describe the process of esterification involving a carboxylic acid and an alcohol. Include conditions and the role of catalysts. (6 marks)

Answer: Esterification is a reversible reaction where a carboxylic acid reacts with an alcohol in the presence of an acid catalyst, such as sulphuric acid, under heating. The acid catalyst protonates the carbonyl oxygen, increasing its electrophilicity, facilitating nucleophilic attack by the alcohol's hydroxyl group. The resulting ester and water are formed, with equilibrium typically shifted by removing water or using excess alcohol.

Question 2: Explain why carboxylic acids are used in the manufacture of vinegar and how their chemical properties make them suitable for this purpose.

Answer: Carboxylic acids like acetic acid are used in vinegar because they impart a sour taste and preservative properties. Their weak acidity inhibits microbial growth, making vinegar a suitable preservative for food products.

Question 1: Describe how carboxylic acids are used in the production of pharmaceuticals or cleaning products.

Answer: Carboxylic acids like salicylic acid are used in pharmaceuticals for acne treatment, while their derivatives are used in cleaning products for their antimicrobial and degreasing properties.

Question 2: Discuss the environmental impact of carboxylic acids released into water systems and how they can be mitigated.

Answer: Carboxylic acids can lower pH and harm aquatic life. Mitigation includes proper waste treatment, neutralisation with bases, and reducing industrial discharge to prevent environmental damage.