Question 1: Alkanes are saturated hydrocarbons with the general formula CnH2n+2. They are the main components of crude oil and are used as fuels. Describe the key characteristic that distinguishes alkanes from alkenes.

Answer: Alkanes are saturated hydrocarbons with only single bonds between carbon atoms, unlike alkenes which contain at least one double bond.

Question 1: Explain why alkanes are considered chemically less reactive than alkenes.

Answer: Because alkanes have only single bonds, which are relatively stable, making them less reactive than alkenes that have double bonds which are more reactive.

Question 2: Describe the process of fractional distillation used to separate alkanes from crude oil.

Answer: Fractional distillation involves heating crude oil so that its components vaporise at different temperatures, then cooling the vapours to condense the different hydrocarbons, including alkanes, at various levels in a fractionating column.

Question 1: Calculate the number of hydrogen atoms in C8H18 (octane).

Answer: 16

Question 2: A litre of methane (CH4) is burned completely in oxygen. Calculate the volume of carbon dioxide produced at room temperature and pressure, assuming ideal gas behaviour. (Use molar volume = 24 dm³).

Answer: 24 dm³

Question 1: Describe a safe method to test whether a hydrocarbon sample is an alkane or an alkene.

Answer: Add bromine water to the sample. If the bromine decolourises, it indicates the presence of an alkene. If no change occurs, it is likely an alkane, which does not react with bromine under normal conditions.

Question 2: Identify two variables that need to be controlled in an experiment testing the flammability of alkanes.

Answer: Temperature and oxygen availability.

Question 1: A refinery produces a mixture of hydrocarbons including alkanes with chain lengths from C5 to C12. Explain why longer-chain alkanes are less suitable as fuels for cars compared to shorter-chain alkanes.

Answer: Longer-chain alkanes have higher boiling points, are less volatile, and produce more soot when burned, making them less suitable as fuels for car engines which require volatile and cleaner-burning fuels.

Question 2: Discuss the environmental impact of burning alkanes derived from crude oil.

Answer: Burning alkanes releases carbon dioxide, a greenhouse gas contributing to climate change. It also produces sulphur oxides and nitrogen oxides, which can cause acid rain and respiratory problems. Additionally, incomplete combustion can produce carbon monoxide and soot, further harming air quality.

Question 1: Explain how alkanes are used in domestic heating and what safety precautions should be considered.

Answer: Alkanes like methane and propane are used as fuels in domestic heating systems. Safety precautions include ensuring proper ventilation to prevent gas build-up, checking for leaks regularly, and installing safety devices like gas detectors.

Question 2: Describe one technological advancement that utilises alkanes in everyday life or industry.

Answer: The development of catalytic converters in vehicles helps reduce harmful emissions when burning alkanes in petrol, making the combustion process cleaner and more environmentally friendly.