15.1-15.3 Fuels & Crude Oils

What is the main component in natural gas?

• carbon dioxide

• methane

• nitrogen

• oxygen

What is the gas required in the combustion of fossil fuels to produce energy?

• carbon dioxide

• chlorine

• nitrogen

• oxygen

Which statement explains why crude oil has to be separated before being used as fuel?

• It is a non-renewable source of energy.

• It appears as a dark, sticky liquid.

• It is a large molecule of hydrocarbon.

• It is a mixure of hydrocarbons with different properties.

Why can crude oil be separated into different fractions?

• The fractions have different colours.

• The fractions have different boiling points.

• The fractions have different solubilities in water.

• The fractions are in different physical states at room temperature.

Order the steps to show the correct sequence in the fractional distillation of crude oil.

1. The vapour is passed to the fractionating column.

2. The crude oil is heated to 400 ºC and boiling occurs.

3. Fractions with lower boiling points rise further up the fractionating column before they condense.

4. Fractions with higher boiling points are collected at the lower levels of the fractionating column.

• 1, 2, 3, 4

• 2, 1, 3, 4

• 2, 1, 4, 3

• 2, 3, 4, 1

Which sentence about fractional distillation of crude oil is true?

• Natural gas is collected at the bottom of the fractionating column.

• The hydrocarbon with the lowest boiling point remains in the furnace.

• The fractions are collected one after the other during the process.

• Shorter hydrocarbons are collected near the top of the fractionating column.

The diagram shows a fractionating column used to separate crude oil. Which of the following statements is correct?

• Fraction X is more viscous than fraction Z.

• Fraction X is less flammable than fraction Y.

• Fraction Y has a lower boiling point than fraction Z.

• Fraction Y contains molecules of larger molecular masses than fraction Z.

The table shows the boiling points of four crude oil fractions, W, X, Y and Z.

Which statement regarding the fractions is not true?

• Fraction Y is less viscous than fraction Z.

• Fraction X is less flammable than fraction W.

• The molecules in fraction X have a shorter chain length than those in fraction Z.

• The molecular mass of fraction X is greater than that of fraction Y.

The properties of fractions obtained from crude oil depend on the sizes of the molecules in the fractions.

What property would you expect from a fraction containing smaller molecules as compared to a fraction containing larger molecules?

• The fraction with smaller molecules are more flammable.

• The fraction with smaller molecules are more viscous.

• The fraction with smaller molecules condenses more readily.

• The fraction with smaller molecules have higher boiling points.

Biofuels are fuels made from plants and animals. One example is bioethanol, which can be produced by fermenting sugarcane. Carbon dioxide gas is given off during the production of bioethanol, as well as when it is burnt as a fuel. However, this may not result in an overall increase in the amount of carbon dioxide in the atmosphere.

Which statement explains this advantage of bioethanol as a fuel?

• A similar amount of carbon dioxide is removed from the atmosphere due to photosynthesis in the sugarcane plants.

• A similar amount of carbon dioxide is used up by the sugarcane plants during respiration.

• Bioethanol is a renewable resource.

• The combustion of bioethanol produces less carbon dioxide per carbon atom.