Question 1: Define an alkane and describe its general molecular structure.

Answer: An alkane is a saturated hydrocarbon with only single bonds between carbon atoms, having the general molecular formula CnH2n+2.

Question 2: Explain why alkanes are considered saturated hydrocarbons.

Answer: Because all carbon-carbon bonds are single bonds with the maximum number of hydrogen atoms attached, meaning no double or triple bonds are present.

Question 3: Describe the mechanism by which alkanes undergo combustion.

Answer: Alkanes combust via a rapid exothermic reaction with oxygen, producing carbon dioxide, water, and energy, following the general equation: CnH2n+2 + O2 → CO2 + H2O + energy.

Question 1: Calculate the volume of oxygen required to completely combust 50 g of hexane (C6H14). (Molar mass of C6H14 = 86 g/mol, O2 = 32 g/mol).

Answer: Moles of hexane = 50/86 ≈ 0.581 mol; Reaction: C6H14 + 9O2 → 6CO2 + 7H2O; Moles of O2 needed = 0.581 × 9 ≈ 5.229 mol; Volume of O2 = moles × molar volume (24 dm³/mol) ≈ 125.5 dm³.

Question 2: Determine the number of carbon atoms in 2.5 litres of butane (C4H10) at room temperature and pressure.

Answer: Moles = volume / 24 dm³/mol = 2.5 / 24 ≈ 0.104 mol; C4H10 molar mass = 58 g/mol; mass = 0.104 × 58 ≈ 6.03 g; Number of C atoms = 4 × moles = 0.416 mol of C atoms.

Question 1: Outline the key safety precautions that must be observed when handling liquefied petroleum gases (LPG) in a domestic setting.

Answer: Ensure proper ventilation, avoid sources of ignition, use appropriate regulators and fittings, store in well-ventilated areas, and handle with care to prevent leaks and explosions.

Question 2: Describe a simple experiment to test whether a hydrocarbon is an alkane or an alkene, including the expected result.

Answer: Add bromine water to the hydrocarbon and observe the colour change. An alkane will not decolourise bromine water, indicating no double bonds, whereas an alkene will decolourise it due to addition across the double bond.

Question 1: A company produces bottled gas containing predominantly butane (C4H10). If the bottle contains 12 litres of gas at room temperature and pressure, estimate the number of moles of butane present.

Answer: Moles = volume / 24 dm³/mol = 12 / 24 = 0.5 mol.

Question 2: Explain why alkanes like butane are used as fuels in portable lighters and camping stoves.

Answer: Because they are easily liquefied under pressure, release a lot of energy when burned, and are relatively safe to handle with proper precautions.