Question 1: Define neutralisation in the context of acids and alkalis.

Answer: Neutralisation is a chemical reaction where an acid reacts with an alkali to produce a salt and water, typically resulting in a solution with a pH close to 7.

Question 2: Explain how neutralisation reactions are utilised in forensic investigations involving bloodstains.

Answer: In forensics, acid solutions can be used to neutralise bloodstains containing alkaline components, or vice versa, to help identify and analyse blood evidence through pH changes or chemical reactions.

Question 3: Describe the mechanism by which an acid neutralises an alkali at the molecular level.

Answer: An acid donates hydrogen ions (H⁺) which react with hydroxide ions (OH⁻) from the alkali to form water molecules, effectively cancelling out each other's reactive properties.

Question 1: Calculate the volume of 0.1 mol/dm³ hydrochloric acid (HCl) needed to neutralise 50 cm³ of a solution containing 0.2 mol/dm³ sodium hydroxide (NaOH).

Answer: 25 cm³

Question 2: A forensic scientist adds 10 mL of an alkali solution to a pH indicator, which turns colour. If the solution is 0.05 mol/dm³ potassium hydroxide (KOH), how many moles of KOH are present?

Answer: 5 × 10⁻⁴ moles

Question 1: Design a basic procedure to determine the concentration of an unknown acid solution found at a crime scene, ensuring safety precautions are addressed.

Answer: Prepare a titration setup with a burette filled with a standard alkali solution of known concentration. Add a few drops of a suitable pH indicator to the unknown acid sample. Slowly add the alkali from the burette to the acid, swirling constantly until the indicator changes colour to show neutralisation. Record the volume used. Repeat to obtain consistent results. Safety precautions include wearing gloves and goggles, handling acids and alkalis carefully, and disposing of chemicals according to safety guidelines.

Question 1: A forensic report states that 25 mL of an unknown acid neutralised 15 mL of a 0.1 mol/dm³ sodium hydroxide solution. What is the concentration of the unknown acid? (Assume a 1:1 molar ratio).

Answer: 0.06 mol/dm³

Question 2: If the pH of a neutralisation mixture at the crime scene is found to be 7, explain what this indicates about the solution and how it relates to forensic analysis.

Answer: A pH of 7 indicates a neutral solution, suggesting that the acid and alkali have fully reacted. In forensic analysis, this confirms the complete neutralisation of reactive substances, aiding in the identification of substances involved.

Question 1: Explain how neutralisation reactions are used in wastewater treatment plants to neutralise harmful acids or alkalis before release into the environment.

Answer: Wastewater treatment plants add neutralising agents such as lime (calcium oxide) or sodium carbonate to acidic or alkaline effluents to bring the pH to near neutral, preventing environmental damage and ensuring regulatory compliance.

Question 2: Discuss the importance of neutralisation reactions in pharmaceutical formulations, particularly in antacid medications.

Answer: Neutralisation reactions are crucial in pharmaceuticals for controlling pH and reducing acidity or alkalinity. In antacids, compounds like magnesium hydroxide or calcium carbonate neutralise excess stomach acid, providing relief from indigestion and preventing damage to the stomach lining. Proper neutralisation ensures the medication's effectiveness and safety.