Carbon Chemistry (AQA GCSE Combined Science: Synergy: Physical Sciences): Exam Questions

This question is about hydrocarbons.

Methane is a hydrocarbon with the formula CH₄

FIGURE 10 shows part of the dot and cross diagram that represents a methane molecule.

Complete the dot and cross diagram for the methane molecule. [1 mark]

Crude oil is a mixture of compounds.

Most of the compounds in crude oil are hydrocarbons.

The hydrocarbons can be separated into fractions by fractional distillation.

FIGURE 11 shows a fractional distillation column.

Explain how the hydrocarbons in crude oil are separated into fractions by fractional distillation. [4 marks]

Explain how the size of the molecules in kerosene and fuel oil affects their:

• relative viscosity

• relative flammability.

Use FIGURE 11, on page 32. [2 marks]

C₁₀H₂₂ is a hydrocarbon in the kerosene fraction.

How does the formula show that C₁₀H₂₂ is an alkane? [1 mark]

This question is about hydrocarbon fuels.

The complete combustion of a hydrocarbon fuel produces carbon dioxide and one other product.

Name the other product of the complete combustion of a hydrocarbon fuel.

Do not refer to carbon dioxide. [1 mark]

Describe the test for carbon dioxide.

Give the result if carbon dioxide is present. [2 marks]

Test __________________________________________________

Result_________________________________________________

The combustion of hydrocarbon fuels releases energy.

A student investigated the energy released by three different fuels A, B and C.

FIGURE 1 shows the apparatus.

This is part of the method used.

1. Put fuel A in the burner.

2. Pour 100 cm³ of water into the conical flask.

3. Record the temperature of the water.

4. Light the fuel and heat the water for 5 minutes.

5. Record the final temperature of the water.

6. Repeat steps 1 to 5 using fuel B and then using fuel C.

The student also determined the mass of fuel burnt.

Describe how the student could determine the mass of fuel burnt. [2 marks]

Give one control variable in the investigation. [1 mark]

TABLE 1 shows the results.

TABLE 1

Explain how TABLE 1 shows that fuel C released the most energy per gram of fuel. [2 marks]

The student repeated the investigation with screens around the apparatus.

FIGURE 2 shows the apparatus with screens.

Give one reason why putting screens around the apparatus could improve the accuracy of the investigation. [1 mark]

How would stirring the water improve the accuracy of the investigation? [1 mark]

This question is about carbon and hydrocarbons.

Which is a form of carbon?

Graphite is a form of carbon.

Which is a property of graphite?

Buckminsterfullerene is a carbon molecule.

What is the formula of buckminsterfullerene?

Hydrocarbons are molecules made up of hydrogen atoms and carbon atoms only.

Ethane is a hydrocarbon.

FIGURE 4 represents an ethane molecule.

FIGURE 4

Complete the formula of an ethane molecule.

C_ H_

FIGURE 5 represents a bond between a carbon atom and a hydrogen atom in ethane.

Which TWO words describe the C—H bond in ethane?

Tick TWO boxes.

FIGURE 6 shows the percentage (%) of different hydrocarbon fractions in a sample of crude oil.

FIGURE 6

Determine the percentage of LPG AND the percentage of fuel oil in this sample of crude oil.

Complete the following steps.

Calculate the total percentage of petrol, diesel oil and kerosene.

Calculate the total percentage of LPG and fuel oil.

Calculate the percentage of LPG AND the percentage of fuel oil.

Use the ratio:

Percentage of LPG : percentage of fuel oil = 3 : 1

Percentage of LPG =_________________________%

Percentage of fuel oil =_______________________%

Fractional distillation is used to separate crude oil into hydrocarbon fractions.

FIGURE 7 shows a fractional distillation column.

FIGURE 7

Complete the sentences.

Choose answers from the list below.

   The liquid crude oil is heated and the hydrocarbons _____________ .

The hydrocarbons rise up the column.

The hydrocarbons cool and _________________ .

Complete the sentence.

Choose the answer from the list below.

  The hydrocarbons separate at different temperatures because each hydrocarbon has a different __________ .

Large hydrocarbon molecules can be broken down into smaller hydrocarbon molecules.

What is the name of this type of reaction?

This question is about hydrocarbons.

Hexane (C₆H₁₄) and pentane (C₅H₁₂) are hydrocarbons in the same homologous series.

Give the name of the homologous series that includes hexane and pentane.

Give the general formula of the homologous series that includes hexane and pentane.

Explain why the boiling point of hexane is higher than the boiling point of pentane.

Complete the equation for the cracking of hexane (C₆H₁₄) into ethene and one other molecule.

C₆H₁₄ → C₂H₄ + _

Methane undergoes complete combustion with oxygen.

Figure 10 represents the equation for the reaction.

Figure 10: CH₄ + 2 O=O → 2 H–O–H + O=C=O

(Methane (4 C–H bonds) + 2 oxygen molecules (each with one O=O double bond) → 2 water molecules (each with two O–H bonds) + 1 carbon dioxide molecule (with two C=O double bonds).)

The energy released forming the new bonds is 814 kJ/mol greater than the energy needed to break the existing bonds.

Table 4 shows some bond energy values.

Table 4

Calculate value Y in Table 4.

This question is about hydrocarbons.

Name the two elements in a hydrocarbon.

Which two of the following substances are hydrocarbons?

Tick (✓) two boxes.

C₆H₁₄ is a hydrocarbon.

C₆H₁₄ can be broken down into smaller molecules.

Complete the equation for the breakdown of C₆H₁₄ into smaller molecules.

C₆H₁₄ → C₄H₁₀ + _

What is the name of the process that breaks down C₆H₁₄ into smaller molecules?

Tick (✓) one box.

How does the boiling point of C₆H₁₄ compare with the boiling point of C₄H₁₀?

Give one reason for your answer.

Tick (✓) one box.

Reason: ___________________________________________

The complete combustion of C₆H₁₄ produces water and one other product.

Name the other product of the complete combustion of C₆H₁₄.

Do not refer to water in your answer.

Hydrocarbons are used to make useful products.

What are the elements in hydrocarbons?

Tick (✓) one box.

Ethene can be produced from long-chain hydrocarbons by cracking.

Give the conditions needed for cracking.

There are several different forms of carbon and many different carbon compounds.

Figure 6 shows a 3D model of a molecule of methane (CH₄) — a tetrahedral arrangement with one carbon atom at the centre and four hydrogen atoms at the corners.

Draw the 2D structure of a methane molecule.

Different forms of carbon have different bonding and structure.

Draw one line from the form of carbon to the bonding and structure.

Forms of carbon (left):

• A 3D tetrahedral structure (each carbon bonded to four neighbours) — diamond

• A structure showing several stacked layers of hexagonally-bonded carbon atoms — graphite

• A single layer of hexagonally-bonded carbon atoms — graphene

Bonding and structure (right):

• Each carbon atom is bonded to three other carbon atoms in a single layer

• Each carbon atom is bonded to four other carbon atoms

• Layers of carbon atoms with no covalent bonds between the layers

• Carbon ions held together by strong electrostatic forces

• Pairs of carbon atoms with no covalent bonds between the molecules

Crude oil is a mixture of many different carbon compounds.

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

Figure 7 shows a fractional distillation column used to separate crude oil (a tall vertical column, heated at the base; fractions are removed at different heights — refinery gases near the top, then petrol, kerosene, diesel oil, fuel oil and bitumen lower down).

Complete the sentences. Use words from the box.

Box: condense, evaporate, freeze

Crude oil is heated so that most of the compounds .

At different temperatures the compounds cool and .

Which fraction is the most viscous?

Tick (✓) one box.

Which fraction is the most flammable?

Tick (✓) one box.

Why does kerosene separate out of the mixture before diesel oil?