Question 1: Define oxygen and explain its importance in biological and industrial processes.

Answer: Oxygen is a colourless, diatomic gas essential for respiration in living organisms and combustion in industry. It supports the process of oxidation and is vital for energy release in cells.

Question 2: Describe the chemical mechanism by which oxygen supports combustion.

Answer: Oxygen reacts with combustible substances in an exothermic reaction, forming oxides. It provides the necessary oxidising agent to sustain flames by accepting electrons from the fuel during oxidation.

Question 3: Explain why a glowing splint relights in the presence of oxygen.

Answer: A glowing splint relights because oxygen reacts with the carbon and other elements in the splint, re-igniting the combustion process due to oxidation.

Question 1: Calculate the volume of oxygen required to completely combust 50 grams of methane (CH₄). Use the reaction: CH₄ + 2O₂ → CO₂ + 2H₂O. (Molar mass of CH₄ = 16 g/mol, molar volume of gas = 24 dm³/mol).

Answer: 150 dm³

Question 2: If a sample contains 20 dm³ of oxygen at room temperature and pressure, how many moles of oxygen does it contain? (Use molar volume = 24 dm³/mol).

Answer: 0.83 mol

Question 1: Describe the procedure to test for the presence of oxygen gas using a glowing splint, including safety precautions.

Answer: Insert a glowing splint into the test tube containing the gas. If the splint relights, oxygen is present. Safety precautions include ensuring the gas is contained in a well-ventilated area, avoiding inhalation of gases, and handling the splint carefully to prevent burns.

Question 2: Identify two variables you could change in a practical test to improve the accuracy of detecting oxygen.

Answer: Using a more pure sample of oxygen and ensuring the splint is fully ignited before testing.

Question 1: A student collects a gas that relights a glowing splint but does not support combustion with a lit splint. What does this indicate about the gas? Explain your reasoning.

Answer: This indicates that the gas is oxygen because it supports re-ignition of a glowing splint but does not support a flame when lit directly, suggesting it is pure oxygen rather than a mixture.

Question 1: Explain how oxygen is used in medical treatments and why its purity is important.

Answer: Oxygen is used in hospitals to support patients with respiratory problems. Its purity is crucial to prevent contamination and ensure effective oxygen therapy, avoiding harmful impurities.

Question 2: Discuss the industrial process of producing oxygen and one safety consideration associated with its storage.

Answer: Oxygen is produced industrially by fractional distillation of liquefied air. Safety considerations include preventing rapid expansion or leaks, as oxygen supports combustion and can cause materials to ignite more easily.

Question 1: Describe an experiment to demonstrate that oxygen supports combustion. Include the steps, variables, and safety precautions. (6 marks)

Answer: Set up a test tube with a glowing splint inside. Prepare a container with pure oxygen gas. Carefully introduce the oxygen into the test tube ensuring no leaks. Insert the glowing splint into the oxygen; it should relight if oxygen supports combustion. Variables include gas purity and splint condition. Safety precautions include handling gases in a well-ventilated area, wearing safety goggles, and avoiding ignition sources near oxygen storage due to fire risk.