Cracking & alkenes

Crude oil is a mixture of hydrocarbons.

The majority of hydrocarbons in crude oil belong to one homologous series.

Give the name of this series.

When hydrocarbons undergo combustion, water is produced.

Draw a dot and cross diagram of a molecule of water.

One compound in crude oil contains 0.96 g of carbon atoms combined with 0.32 g of hydrogen atoms.

Calculate the empirical formula of this compound.

(relative atomic masses: C = 12, H = 1.0)

*(d) Crude oil is separated into useful products called fractions using fractional distillation.

Figure 14 shows a fractional distillation column and the fractions kerosene and fuel oil.

Kerosene and fuel oil have different uses depending on their properties.

Describe the properties and uses of kerosene and fuel oil. Include in your answer

• the difference in boiling point

• the difference in viscosity

• the difference in ease of ignition

• their uses and how fuel oil can be converted into kerosene.

Crude oil is a mixture of hydrocarbons.

Crude oil can be separated into useful fractions by the process of fractional distillation in a fractionating column.

Figure 15 shows a fractionating column, the fractions obtained and the trend in viscosity of the fractions.

Which row shows the correct uses for bitumen, diesel oil and fuel oil?

Explain the trend in the viscosity of the fractions.

Hydrocarbon X was cracked to form one molecule of hexane, C₆H₁₄, and one molecule of alkene Y.

The relative formula mass of Y is 56. The empirical formula of Y is CH₂.

Deduce the molecular formula of hydrocarbon X.

Show your working.

(relative atomic masses: H = 1.0, C = 12)

*(c) Large quantities of methane are used as a fuel.

Figure 16 shows a Bunsen burner.

Methane can be used as fuel for the Bunsen burner.

The air-hole on the chimney of the Bunsen burner can be opened and closed.

Explain the effect of opening and closing the air-hole of the Bunsen burner on the products of combustion of methane and the harm that using large quantities of methane as a fuel can cause.

Pentadecane, C₁₅H₃₂, is a hydrocarbon and is used as a fuel.

The incomplete combustion of pentadecane produces carbon monoxide. Carbon monoxide is a toxic gas.

Explain why the incomplete combustion of pentadecane can produce carbon monoxide as one of the products.

Explain how carbon monoxide behaves as a toxic gas.

1 mole of pentadecane can be cracked to form 1 mole of octane, C₈H₁₈, and 1 mole of propene, C₃H₆, and 2 moles of another product.

Complete the balanced equation for this reaction by adding the formula of the missing product.

Figure 11 shows the reaction of propene, C₃H₆, with water.

H H H

Figure 11

Figure 12 shows some bond energies.

Use the bond energies in Figure 12 to calculate the energy change of the reaction in Figure 11.

energy change of reaction =_........ kJ

Methane gas, CH₄, was burned using the apparatus shown in Figure 13.

Explain why water droplets form on the bottom of the beaker of cold water.

Methane is a hydrocarbon fuel.

Complete the word equation for the complete combustion of methane in oxygen.

methane +_........ water +_........

The incomplete combustion of methane can produce carbon and carbon monoxide.

Give the reason why carbon and carbon monoxide are produced in the incomplete combustion of methane.

Crude oil is a complex mixture of hydrocarbons. Crude oil can be separated into useful fractions by fractional distillation.

Figure 10 shows a fractional distillation column and the fractions produced when crude oil is distilled.

Name the fraction in Figure 10 that is used to surface roads.

Name the fraction in Figure 10 that contains hydrocarbons with the lowest boiling point.

When crude oil is fractionally distilled, the demand for some fractions is more than the amount produced.

Figure 11 shows the relative amounts of each fraction in a crude oil and the relative demand for each of these fractions.

Which of the following shows the fractions where the relative demand is greater than the relative amount in the crude oil?

Cracking involves the breaking down of large hydrocarbon molecules into smaller hydrocarbon molecules.

Octane, C₈H₁₈, can be cracked to produce one molecule of ethene, C₂H₄, and one molecule of C_xH₁₄.

Determine the value of x in the molecule of C_xH₁₄.

Dodecane is a large hydrocarbon molecule. When one molecule of dodecane is cracked the products are one molecule of octane and one molecule of butene.

dodecane octane + butene

Calculate the maximum mass of octane that could be produced when 340 g of dodecane is cracked in this reaction.

(relative formula masses: dodecane = 170, octane = 114)

Propene can be produced by the cracking of some hydrocarbons obtained from crude oil.

The equation shows the cracking of one molecule of decane to produce one molecule of butene and one molecule of another product.

decane butene

Calculate the values of x and y in C_xH_y.

State the total mass of products formed if 25 g of decane is cracked in this way.

The structure of a molecule of ethene is shown in Figure 8.

Figure 9 shows the incomplete dot and cross diagram for a molecule of ethene.

Complete Figure 9 to show the electrons of the C C double bond.

The incomplete combustion of ethene in air produces water as one of the products.

Give the name of another product of the incomplete combustion of ethene.

Substance X is an unsaturated hydrocarbon. The structure of a molecule of substance X is shown in Figure 10.

Explain how the structure of substance X shows that it is an unsaturated hydrocarbon.

Two liquid hydrocarbons, A and B, were tested with bromine water. One hydrocarbon was known to be an alkane. The other hydrocarbon was known to be an alkene.

Each hydrocarbon was shaken with a few drops of bromine water.

The results of the tests were hydrocarbon A + bromine water: the mixture turned from orange to colourless. hydrocarbon B + bromine water: the orange colour remained.

Explain these results.

(a) Figure 10 shows information about a glass, a ceramic, a polymer and a metal.

*polymers soften, rather than melt, when heated.

Figure 10

Figure 11 shows part of a household wire that connects a kettle to a plug.

Figure 11

Why is this wire made of metal?

Which type of material would be most suitable for the insulation on this household wire?

Explain, using information from Figure 10, why the ceramic is a suitable material to make a cup that will contain a hot drink of tea or coffee.

The structure of a molecule of a polymer is shown in Figure 12.

Complete the structure of a molecule of the monomer used to make this polymer by adding the missing covalent bonds.

*(ii) Poly(ethene) has many uses in everyday life. Large amounts of poly(ethene) are manufactured from ethene produced by cracking fractions obtained from crude oil.

Poly(ethene) is used to make many objects. After use it is necessary to dispose of the large amounts of poly(ethene) in these objects.

Explain some of the problems associated with the manufacture and disposal of poly(ethene).

Crude oil is a complex mixture of substances.

Crude oil can be separated into useful fractions by fractional distillation.

Figure 7 shows a fractional distillation column and the fractions produced when a sample of crude oil is distilled.

The properties of these fractions vary from the top of the column to the bottom of the column.

Which of the following is a trend in a property of the fractions obtained from the top of the column to those obtained from the bottom?

Most of the substances in crude oil are alkanes.

Explain why alkanes are described as hydrocarbons.

Figure 8 shows a graph of the boiling points of some alkanes against the number of carbon atoms in one molecule of each alkane.

Explain the pattern shown by this graph.

Use the information in Figure 9 to give the name of the fraction that is most likely to need to be cracked.

_........

In a cracking reaction, reactants are heated to form products. This reaction is endothermic.

On the axes provided, draw the reaction profile of this reaction. Label the energy of the reactants, the energy of the products and the activation energy of the reaction.

Dodecane, C₁₂H₂₆, can be cracked to form useful products.

Complete the equation for the cracking of dodecane by filling in the formula of the single molecule needed to balance the equation.