Diamond, graphite, graphene & fullerenes

This question is about carbon and some carbon compounds.

Two forms of pure carbon are graphite and Buckminsterfullerene.

Explain why graphite is used as a lubricant.

Calculate the mass, in kg, of five moles of Buckminsterfullerene, C₆₀.

(relative atomic mass: C = 12)

A molecule in an homologous series has the formula C₉H₂₁N.

What is the formula of the next molecule in this homologous series?

A Bunsen burner burns methane gas, CH₄.

A student investigates the time taken to heat up a beaker of water using this Bunsen burner.

Figure 9 shows the apparatus used.

The student sees that a large amount of carbon forms as a black solid on the underside of the gauze.

The teacher said that the investigation would be improved if no carbon forms.

Explain what the student should do to stop carbon forming on the underside of the gauze.

*(d) Natural processes and human activities change the amount of carbon dioxide in the atmosphere.

Figure 10 shows the concentration of carbon dioxide in the atmosphere measured in one location and the mean global temperature from 1960 to 2000.

Evaluate whether the data in Figure 10 shows that the change in the amount of carbon dioxide is leading to climate change.

Your answer should include

• the natural processes that change the amount of carbon dioxide in the atmosphere

• the human activities that change the amount of carbon dioxide in the atmosphere

• how carbon dioxide contributes to the greenhouse effect and climate change.

A 250 cm³ solution of copper sulfate contains 6.52 g of dissolved solid.

Calculate the concentration of this copper sulfate solution in g dm^–3.

concentration =_........ g dm

Sodium hydroxide solution and copper sulfate solution were reacted together completely.

The result was a mixture of a precipitate of copper hydroxide in a solution of sodium sulfate.

Describe how to obtain

• a pure sample of solid copper hydroxide from the mixture

• a pure sample of solid sodium sulfate from the mixture.

Figure 9 shows the equipment used to electrolyse a sample of sodium sulfate solution.

Graphite electrodes are used in the electrolysis.

Give two reasons why graphite is a suitable material for the electrodes.

Sodium sulfate solution contains ions.

Which ions are attracted to the positive electrode during the electrolysis?

Draw one straight line from each electrode to the product formed at that electrode during the electrolysis of sodium sulfate solution.

This question is about the properties of different substances.

Silicon tetrachloride is a simple molecular covalent compound.

A molecule of silicon tetrachloride is composed of a silicon atom and four chlorine atoms.

• a silicon atom has 4 outer electrons

• a chlorine atom has 7 outer electrons

Draw a dot and cross diagram of a molecule of silicon tetrachloride, SiCl₄.

Show outer electrons only.

Explain why simple molecular covalent compounds such as silicon tetrachloride have low melting and boiling points.

Part of the structure of rubidium bromide is shown in Figure 7.

Which row shows the most likely melting point and boiling point of rubidium bromide?

*(c) Diamond and graphite are two forms of carbon.

Figure 8 shows how the carbon atoms are arranged in a part of the structure of each of these forms of carbon.

• diamond is one of the hardest known substances on Earth and is used in cutting tools.

• graphite is soft and flaky.

• diamond is a poor electrical conductor, but graphite is a good electrical conductor.

Explain, in terms of structure and bonding, these properties of diamond and graphite.

3.14 g of solid copper sulfate was dissolved in water and made up to 250 cm³ of solution.

Calculate the concentration of this copper sulfate solution in g dm⁻³.

concentration =_........ g dm

Sodium hydroxide solution was added to a solution of copper sulfate. A precipitate of copper hydroxide and a solution of sodium sulfate were formed.

State what would be seen in the reaction.

Complete the balanced equation for the reaction by adding a number in front of NaOH.

Describe how to obtain a pure, dry sample of the precipitate of copper hydroxide from the reaction mixture.

Figure 11 shows the ions in the sodium sulfate solution.

Draw a circle around each of the ions in Figure 11 that are attracted to the negative graphite electrode during the electrolysis.

State why it is important that the electrodes are inert.

Explain, in terms of its structure, how graphite conducts electricity.

Bromine is a liquid at room temperature and vaporises readily. Bromine has a simple molecular structure.

Which row of the table shows the most likely melting and boiling points of bromine?

Part of the structure of graphene is shown in Figure 5.

Explain why graphene will be a good conductor of an electric current.

Part of the structure of potassium chloride is shown in Figure 6.

Potassium chloride has a melting point of 770 °C.

Explain why potassium chloride has a high melting point.

*(d) A molecule of methane can be represented in several different ways as shown in Figure 7. These representations have been labelled A – E to assist you in your answer.

Describe what information can be obtained from each representation including the limitations of these representations of methane.

Hydrochloric acid reacts with solid B. Solid B is an alkali.

A student carries out an experiment to see how the pH changes when different masses of solid B are added to dilute hydrochloric acid.

The student uses the following method.

step 1 use a measuring cylinder to measure out 100cm³ of dilute hydrochloric acid

step 2 pour the acid into a beaker

step 3 measure the pH with a pH probe

step 4 add half a spatula of solid B and stir

step 5 repeat steps 3 and 4 until the pH stops changing.

Give a safety precaution that should be taken during the experiment.

Give an improvement to step 4 that would produce more accurate results.

What is the most likely change in pH during the experiment?

If some methyl orange indicator is added to the acid in step 2, the mixture changes colour during the experiment.

State the colour change.

colour at start in acid_........ colour at end_........

Concentrated hydrochloric acid can be broken down using electricity. The apparatus that can be used is shown in Figure 6.

Give the name of the piece of apparatus labelled X.

The rod labelled Y in Figure 6 is made of graphite.

What is the name of this piece of apparatus?

Give one reason why graphite is a suitable material to make Y.

Complete the balanced equation for the reaction that occurs.

The molecular formula of butene is C₄H₈.

Which of the following is the empirical formula of butene?

Calculate the relative formula mass of butene, C₄H₈.

(relative atomic masses: H = 1, C = 12)

relative formula mass_........

When burnt completely in air, butene forms carbon dioxide and water.

Balance the equation for this reaction by putting numbers in the spaces provided.

Describe the test to show that a gas is carbon dioxide.

Substance X is a gas at room temperature. It is a simple molecular, covalent substance.

Which row of the table shows the properties that substance X is most likely to have?

Diamond has a giant covalent structure.

State one property of diamond that is the result of its giant covalent structure.

Covalent substances can be simple molecular covalent or giant covalent.

Ammonia is a simple molecular, covalent substance.

Which is the most likely set of properties for ammonia?

Ammonia, NH₃, is made by reacting nitrogen with hydrogen.

Write the balanced equation for this reaction.

Oxygen, O₂, is also a simple molecular, covalent substance.

Draw a dot and cross diagram for the molecule of oxygen.

*(c) Figure 8 shows the arrangement of carbon atoms in diamond, graphene and a fullerene (C₆₀).

Consider these three substances.

Explain, in terms of their structures and bonding, their relative melting points, strengths and abilities to conduct electricity.