Properties of hydrocarbons

Butane (C₄H₁₀) is an alkane.

Explain why butane is a saturated hydrocarbon.

When butane burns completely in oxygen, carbon dioxide and water are produced.

Give a chemical equation for this combustion reaction.

Incomplete combustion can occur when the oxygen supply is limited.

One product of the incomplete combustion of butane is carbon monoxide.

Give the name of another product of this incomplete combustion.

State why carbon monoxide is poisonous to humans.

C₄H₁₀ exists as two isomers.

State what is meant by the term isomers.

Draw the displayed formula of each isomer.

Explain why hexane (C₆H₁₄) has a higher boiling point than butane (C₄H₁₀).

A student uses this apparatus to investigate the heat energy released when a liquid fuel burns.

This is the student’s method.

• measure the mass of the spirit burner and fuel

• add 100 g of water to the aluminium can

• measure the temperature of the water

• use the spirit burner to heat the water until the temperature rises by 50 °C

• measure the new mass of the spirit burner and fuel

Give a reason why the student uses an aluminium can rather than a glass beaker.

When the fuel burns, a black solid forms on the aluminium can.

Identify the black solid.

Give a reason why the black solid forms.

Show that the heat energy needed to raise the temperature of 100 g of water by 50 °C is approximately 20 000 J.

[for water, c = 4.2 J/g/°C]

The student burns 1.84 g of ethanol.

Calculate the molar enthalpy change, Δ H, in kJ/mol, for the combustion of ethanol.

Include a sign in your answer.

[for ethanol, M_r = 46]

ΔH =_........ kJ/mol

In a different experiment, the student burns 3.7 g of butanol.

This is an equation for the incomplete combustion of butanol.

Complete the equation for the incomplete combustion of butanol.

Calculate the total amount, in moles, of gas produced by the incomplete combustion of 3.7 g of butanol.

This question is about methane, CH₄

The diagram shows a Bunsen burner that uses methane.

During combustion, methane reacts with a gas in the air.

Give the name of this gas.

Give the two products of the complete combustion of methane.

During the incomplete combustion of methane, carbon monoxide forms.

Give a reason why carbon monoxide forms during incomplete combustion.

State why carbon monoxide is poisonous.

The equation shows the reaction of methane with bromine.

Give the name of this type of chemical reaction.

A student uses this apparatus to find the heat energy released by the combustion of liquid fuels.

Explain what is meant by the term fuel.

In one experiment, the student uses liquid ethanol as the fuel.

The thermometer shows the temperature of the water at the start of the experiment.

Complete the table by giving the temperatures to the nearest 0.1 °C.

The metal can contains water of mass 150 g.

Show, by calculation, that the heat energy change (Q) for this reaction is approximately 36 000 J.

[for water, c = 4.2 J/g/°C]

In the experiment, 2.3 g of ethanol (M_r = 46) is burned.

Calculate the molar enthalpy change (Δ H), in kJ/mol, for the combustion of ethanol, C₂H₅OH

Include a sign in your answer.

Give your answer to two significant figures.

In this experiment, the calculated value of Δ H is less than the value given in a data book.

Give a possible reason for the difference in values.

A teacher uses this apparatus to test the products of the combustion of liquid hydrocarbons.

Explain the change in appearance that occurs in the limewater.

The equation represents the complete combustion of an alkene.

C_nH_2n + oxygen carbon dioxide + nH₂O

Complete combustion of 0.0100 mol of the alkene produces 2.16 g of water.

Determine the molecular formula of this alkene.

[for H₂O, M_r = 18]

Give a reason why the mass of pure water that collects in the U-tube is less than 2.16 g.

Give a physical test to show that the water that collects in the U-tube is pure.

The teacher burns 30.0 g of heptane.

This is the equation for the complete combustion of heptane.

Calculate the minimum mass of oxygen needed for the complete combustion of 30.0 g of heptane.

[for C₇H₁₆, M_r = 100 for O₂, M_r = 32]

A student uses this apparatus to find the molar enthalpy change (Δ H) of combustion for the liquid fuel, pentanol.

This is the student’s method.

• find the initial mass of the spirit burner and pentanol

• add 100 cm³ of water to the copper can

• record the initial temperature of the water

• light the wick of the spirit burner to heat the water

• stir the water until the temperature rises by 35.0 °C

• extinguish the flame and immediately find the final mass of the spirit burner and pentanol

State why the student stirs the water.

Suggest why it is important that the student immediately finds the final mass of the spirit burner and pentanol.

The diagram shows the initial temperature of the water.

Complete the table to show the temperature readings.

Give both values to the nearest 0.1 °C.

Show by calculation that the heat energy (Q) supplied by the pentanol is approximately 15 000 J.

[for water, c = 4.2 J / g / °C]

[for 1.0 cm³ of water, mass = 1.0 g]

The table gives the initial and final mass readings.

Use your answer to part (c)(i) and the information in the table to calculate the molar enthalpy change (Δ H) of combustion, in kJ / mol, for pentanol.

[for pentanol, M_r = 88]

Include a sign in your answer.

ΔH for pentanol =_........ kJ / mol

The formula of pentanol is C₅H₁₁OH

Write a chemical equation for the complete combustion of pentanol.

This question is about alkanes.

Which of these is the molecular formula of an alkane?

Which of these has the same empirical formula and molecular formula?

In the presence of ultraviolet radiation, methane reacts with bromine to form bromomethane and hydrogen bromide.

State the name of this type of reaction.

Give a chemical equation for this reaction.

One mole of an alkane burns completely in oxygen.

The equation represents the reaction.

The numbers x, y and z are used to balance the equation.

The complete combustion of one mole of the alkane produces 220 g of carbon dioxide and 108 g of water.

Calculate the values of y and z.

[M_r of CO₂ = 44 M_r of H₂O = 18]

Determine the molecular formula of the alkane and the value of x.

When an alkane burns in a limited supply of air, incomplete combustion occurs.

Explain why incomplete combustion of an alkane could be harmful to humans.

A student uses this apparatus to find the heat energy supplied by a liquid fuel.

The student burns some fuel to heat the water in the copper container and measures the change in temperature.

The student notices that the bottom of the container turns black.

Give the name of the black substance that forms on the bottom of the container.

In one experiment, the student burns 0.92 g of ethanol.

The student calculates that the heat energy absorbed by the water is 18.2 kJ.

Show that the results of this experiment give an approximate value for the enthalpy of combustion of ethanol of Δ H = –900 kJ/mol.

[M_r of ethanol = 46]

The data book value of Δ H for the combustion of ethanol is –1367 kJ/mol.

Give two reasons why the student’s value is much lower than the data book value.

Calculate the bond energy of the C H bond, using information from the equation and the table.

Complete the energy level diagram to show the products and Δ H.

The diagram shows a fractionating column used to separate crude oil into fractions.

Give a use for bitumen and a use for gasoline.

Explain why bitumen is collected at the bottom of the fractionating column and gasoline is collected near the top of the fractionating column.

There is a low demand for some of the fractions obtained from crude oil.

Cracking can be used to convert these fractions into more useful substances.

State the conditions needed for cracking.

Dodecane (C₁₂H₂₆) can be cracked to produce an alkane and two alkenes.

Complete the equation by giving the formulae of the two alkenes.

A student uses this apparatus to investigate the heat energy released when a liquid fuel is burned.

This is the student’s method.

● measure the mass of the spirit burner and fuel

● add 100 cm³ of water to the copper can

● record the temperature of the water

● use the spirit burner to heat the water until the temperature rises by 30 °C

● immediately measure the new mass of the spirit burner and fuel

Suggest why the student measures the mass of the spirit burner and fuel immediately after heating the water.

When the fuel is burned, the student notices that a black solid forms on the bottom of the copper can.

Identify the black solid.

Explain why the black solid forms.

Show that the heat energy change, Q, to raise the temperature of 100 cm³ of water by 30 °C is approximately 13 kJ.

[c for water = 4.2 J/g/ °C]

The student burns 0.96 g of methanol, CH₃OH

Calculate the molar enthalpy change, Δ H, in kJ/mol, for the combustion of methanol.

Include a sign in your answer.

[M_r of methanol = 32]

ΔH =_........ kJ/mol

The table shows data book values for the molar enthalpy change, Δ H, for the combustion of some alcohols with different numbers of carbon atoms per molecule.

Plot the data values from the table on the grid.

Draw a straight line of best fit.

Number of carbon atoms

Deduce the value of Δ H for an alcohol with six carbon atoms per molecule.

Show on the graph how you obtained your answer.

State the relationship between Δ H and the number of carbon atoms per molecule.

Crude oil is an important source of organic compounds.

The diagram shows crude oil being separated into different fractions.

Name the process used to separate crude oil into different fractions.

State what happens to the crude oil at X.

Describe the differences between fraction B and fraction E.

In your answer, refer to

● size of the molecules

● boiling point

● colour

● viscosity

Crude oil often contains sulfur as an impurity.

Explain why this is a problem when using crude oil fractions as fuels.

Some cars in Brazil use ethanol, C₂H₅OH, as a fuel instead of petrol.

The ethanol is made by the fermentation of glucose which is obtained from sugar cane.

The sugar is extracted from the sugar cane and then dissolved in water to make a sugar solution.

Name the substance that is added to the sugar solution that causes glucose to ferment.

Which temperature is the most suitable for fermentation?

Explain why fermentation is done in the absence of air.

State what is meant by the term fuel.

Write a chemical equation for the complete combustion of ethanol in air.

Ethanol is also manufactured by reacting steam with ethene, C₂H₄

The equation for this reaction is

State the conditions of temperature and pressure used in this process.

When ethanol is heated with acidified potassium dichromate(VI), it is oxidised to ethanoic acid.

State the colour change that occurs in the potassium dichromate(VI) during this reaction.

The structural formula of ethanoic acid is CH₃COOH

Draw the displayed formula of ethanoic acid.

Complete the equation for the reaction of ethanoic acid with sodium.

_........ CH₃COOH(aq) +_........ Na(s) _........ (aq) +_........ (g)