Question 1: Hydrogen is the lightest and most abundant element in the universe. It is a colourless, odourless, and highly flammable gas. In a laboratory, hydrogen can be tested by its reaction with a certain element that produces a characteristic squeaky pop sound. Name this element.

Answer: oxygen

Question 2: Describe the chemical reaction that occurs when hydrogen reacts with oxygen during combustion.

Answer: Hydrogen reacts with oxygen to form water (H₂O), releasing energy: 2H₂ + O₂ → 2H₂O.

Question 3: Which test involves bringing a burning splint into contact with hydrogen gas to produce a distinctive squeaky pop? Explain the science behind this test.

Answer: This test is called the 'hydrogen squeaky pop test'. When a burning splint is introduced into hydrogen gas, the hydrogen ignites and rapidly combusts, producing a loud squeaky pop due to the rapid expansion of gases.

Question 1: State two physical properties of hydrogen gas relevant to its detection in a laboratory setting.

Answer: Hydrogen is colourless and odourless.

Question 2: Explain why hydrogen is considered highly flammable and discuss the safety precautions necessary during testing.

Answer: Hydrogen is highly flammable because it can ignite easily in air with a wide flammability range and low ignition energy. Safety precautions include conducting tests in a well-ventilated area, keeping sources of ignition away, and using proper protective equipment.

Question 1: Calculate the volume of hydrogen gas produced at room temperature (25°C) and pressure (1 atm) when 2 grams of magnesium reacts with excess hydrochloric acid. (Molar mass of Mg = 24.3 g/mol, HCl = 36.5 g/mol).

Answer: Using the reaction: Mg + 2HCl → MgCl₂ + H₂. Moles of Mg = 2 / 24.3 ≈ 0.0823 mol. Moles of H₂ = 0.0823 mol. Volume = mol × 24.0 L/mol = 0.0823 × 24.0 ≈ 1.975 L.

Question 2: If 5 litres of hydrogen gas are collected, how many moles of hydrogen are present? (Use 24.0 L/mol for molar volume at room temperature and pressure).

Answer: Number of moles = Volume / Molar volume = 5 L / 24.0 L/mol ≈ 0.208 mol.

Question 1: Design a simple experiment to test for the presence of hydrogen gas using household materials. Include safety considerations.

Answer: Prepare a test tube with a small amount of hydrogen gas. Bring a lit splint close to the opening of the test tube. If hydrogen is present, it will produce a squeaky pop sound. Safety considerations include ensuring the area is well-ventilated, performing the test away from open flames, and wearing safety goggles.

Question 1: A student collects 2.5 litres of hydrogen gas over water at room temperature. The gas is tested with a lit splint and produces a pop sound. What does this indicate about the gas? What is the main safety concern when performing this test?

Answer: The pop indicates the presence of hydrogen gas. The main safety concern is the risk of fire or explosion due to hydrogen's flammability.

Question 2: Discuss how hydrogen can be used as a clean fuel in industry and the challenges associated with its storage and transportation.

Answer: Hydrogen is considered a clean fuel because it produces water when burnt, emitting no greenhouse gases. It can be used in fuel cells and as a substitute for fossil fuels. Challenges include its high flammability, the difficulty of storing it under high pressure or low temperature, and the need for safe transportation infrastructure.