Question 1: What is hydrogen, and why is it classified as a diatomic gas?

Answer: Hydrogen is a chemical element with the symbol H; it exists as a diatomic molecule (H₂) because two hydrogen atoms bond together to form a stable molecule.

Question 2: Describe the general principle behind the test for hydrogen gas using a lit splint.

Answer: Hydrogen gas produces a characteristic 'pop' sound when a lit splint is inserted into a test tube containing it, indicating the presence of hydrogen.

Question 1: Explain why hydrogen is considered a flammable gas and mention one safety precaution when handling it.

Answer: Hydrogen is flammable because it can easily ignite in air, producing water and releasing energy; safety precautions include working in well-ventilated areas and avoiding sparks or open flames.

Question 2: What is the chemical equation for the reaction between hydrogen and oxygen? Write your answer with state symbols.

Answer: 2H₂(g) + O₂(g) → 2H₂O(l)

Question 1: Calculate the volume of hydrogen gas (at room temperature and pressure) produced when 4 grams of magnesium reacts with hydrochloric acid. Use the reaction: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g). (Molar mass of Mg = 24.3 g/mol)

Answer: The molar amount of Mg = 4 g / 24.3 g/mol ≈ 0.165 mol According to the reaction, 1 mol Mg produces 1 mol H₂. Therefore, 0.165 mol Mg produces 0.165 mol H₂. Using the ideal gas law at room temperature and pressure, 1 mol of gas occupies 24 dm³. Volume of H₂ = 0.165 mol × 24 dm³/mol ≈ 3.96 dm³

Question 1: List two variables that should be controlled during a hydrogen gas test to ensure accurate results.

Answer: Variables include the amount of hydrogen produced and the temperature of the environment.

Question 2: Describe one safety measure that must be taken when performing a hydrogen gas test in the laboratory.

Answer: Perform the test in a well-ventilated area and keep away from open flames or sparks.

Question 1: A student collects a gas over water and notices a pop when a lit splint is inserted. The gas is later confirmed to be hydrogen. What does this data suggest about the gas's properties?

Answer: The gas is flammable and produces a pop sound with a lit splint, indicating it is hydrogen.

Question 2: If a sample of hydrogen gas has a volume of 10 dm³ at room temperature and pressure, how many moles does it contain? (Use 24 dm³/mol for molar volume)

Answer: Number of moles = Volume / Molar volume = 10 dm³ / 24 dm³/mol ≈ 0.417 mol

Question 1: Describe one way hydrogen is used in industry or technology today, and explain why it is suitable for this use.

Answer: Hydrogen is used as a fuel in fuel cells for clean energy production because it produces only water when burned, making it environmentally friendly.

Question 2: Explain the significance of hydrogen in the development of sustainable energy sources.

Answer: Hydrogen is a key component in sustainable energy because it can be produced from renewable resources, stored efficiently, and used in fuel cells to generate electricity with zero emissions, helping reduce reliance on fossil fuels and decrease greenhouse gas emissions.