Question 1: Define relative formula mass and explain how it differs from relative molecular mass.

Answer: Relative formula mass is the sum of the atomic masses of all atoms in a chemical formula, used for ionic compounds. It differs from relative molecular mass, which applies to molecules and includes the actual molecular structure.

Question 2: Why is the concept of relative formula mass important in calculating the amount of substance in automotive fuels?

Answer: It allows chemists to determine the mass of fuel components in relation to moles, helping to optimise fuel efficiency and reduce emissions.

Question 1: Calculate the relative formula mass of gasoline component octane, C8H18.

Answer: C: 8 × 12.01 + 18 × 1.008 = 96.08 + 18.144 = 114.224 g/mol

Question 2: A vehicle's fuel tank contains 50 litres of petrol (density 0.75 g/cm³). How many moles of octane (C8H18) are present in 10 grams of this fuel? (Use relative formula mass of octane = 114.22 g/mol).

Answer: Mass of 50L petrol: 50,000 cm³ × 0.75 g/cm³ = 37,500 g; assuming petrol is mainly octane, moles = 10 g / 114.22 g/mol ≈ 0.0875 mol

Question 1: Describe a simple method to analyse the composition of a fuel sample in terms of its hydrocarbon components. Include safety precautions and variables to consider.

Answer: A method involves collecting a fuel sample, performing a distillation to separate components, and using mass spectrometry or infrared spectroscopy to identify hydrocarbon types. Safety precautions include working in a well-ventilated area, wearing protective equipment, and handling chemicals carefully. Variables include temperature, purity of sample, and calibration of equipment.

Question 1: A report states that a certain type of petrol contains 85% octane by volume. If a fuel sample weighs 37.5 kg, estimate how many moles of octane are present, given the relative formula mass of octane is 114.22 g/mol.

Answer: Volume of octane = 85% of total volume; assuming density similar to pure octane, mass of octane ≈ 37,500 g × 0.85 = 31,875 g; moles = 31,875 g / 114.22 g/mol ≈ 279.2 mol

Question 1: Explain how the concept of relative formula mass can be used to reduce vehicle emissions.

Answer: By calculating the precise amount of each hydrocarbon component in fuel, chemists can optimise fuel formulations to burn more completely, reducing unburned hydrocarbons and pollutants. Accurate mass calculations help in designing cleaner-burning fuels and in evaluating emissions data.