Sec 4 Chemistry Fuels & Hydrocarbons topical questions

State what is meant by a hydrocarbon.

Name the process used to separate crude oil into fractions, and state the property it relies on.

State the trend in viscosity and in flammability of fractions from the top to the bottom of the fractionating column.

Decide whether each hydrocarbon is an alkane or an alkene.

1. (a)C₂H₆[1]
2. (b)C₃H₆[1]
3. (c)C₄H₁₀[1]

Explain why the petrol fraction condenses near the top of the fractionating column while fuel oil condenses near the bottom.

Ethane is bubbled through bromine water in the dark. Nothing happens. The tube is then placed in bright sunlight and the orange colour slowly fades.

1. (a)Name the type of reaction occurring in sunlight.[1]
2. (b)Write the equation for the reaction.[2]
3. (c)Explain why sunlight is needed.[2]

A chemist has two colourless gases, X and Y. Gas X decolourises bromine water immediately; gas Y does not, but burns with a clean blue flame.

1. (a)Identify the family of each gas and explain the bromine result for X.[3]
2. (b)Name one hydrocarbon X could be and write its formula.[2]

State the conditions for cracking, and explain why oil companies crack heavy fractions even though crude oil already contains some petrol.

Ethene is passed over a hot nickel catalyst with hydrogen; in a second experiment, ethene meets steam over a catalyst.

1. (a)Write both equations.[2]
2. (b)Name both organic products and one use of the alcohol product.[2]
3. (c)State the type of both reactions.[1]

Cracking of molecule A (C₁₂H₂₆) gives two products: an alkene with 3 carbon atoms and one other hydrocarbon B.

1. (a)Write the molecular formula of the alkene product and its name.[2]
2. (b)Deduce the formula of B and state its family.[3]
3. (c)Write the full cracking equation.[1]

A refinery has surplus bitumen demand falling, and plastics factories short of ethene. Explain how cracking helps both problems, and write one example equation.

Hydrocarbon W decolourises bromine water immediately. W contains 85.7% carbon and 14.3% hydrogen by mass, and 0.70 g of W occupies 300 cm³ at r.t.p.

1. (a)Show that the empirical formula of W is CH₂.[2]
2. (b)Calculate the moles of W in 0.70 g and hence its molecular formula. (Molar volume = 24 dm³/mol.)[3]
3. (c)Name W and state the observation with bromine water.[1]