Giant Structures (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Chemistry): Exam Questions

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For each of the following unfamiliar elements predict one physical and one chemical property.

Caesium (Cs)

Physical property .............................................................................................................. Chemical property .............................................................................................................

Vanadium (V)

Physical property .............................................................................................................. Chemical property .............................................................................................................

Fluorine (F)

Physical property .............................................................................................................. Chemical property .............................................................................................................

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The following table gives information about six substances.

Which substance could be a metal?

State all the substances that are liquid at room temperature.

Which substance could be propane?

Which substance could be sodium chloride?

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Explain why Na, Mg and Al are good conductors of electricity.

Which element exists as diatomic molecules of the type X₂?

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Sodium chloride is a crystalline solid with a high melting point. It dissolves in water to give a neutral solution. Phosphorus trichloride is a liquid at room temperature. It reacts with water to form an acidic solution.

Suggest an explanation for these differences in properties.

Describe how you could show that magnesium oxide is a basic oxide and not an amphoteric oxide.

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Draw a dot-and-cross diagram showing the bonding in magnesium oxide. Show outer electrons only.

The first three elements, Na, Mg and Al, are metals.

Describe the structure of a typical metal.

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The table shows the melting points, boiling points and electrical properties of five substances, A to E.

Choose a substance from the table above to match each of the following descriptions. A substance may be used once,  more than once or not at all. Justify each choice with evidence from the table. One has been completed as an example.

This substance is covalent and is a solid at room temperature (25 °C): D Evidence: Its melting point is above room temperature. It has a low melting point and it does not conduct as a liquid, so it is covalent.

This substance has a giant covalent structure: Evidence:

This substance is a metal: Evidence:

This substance is a liquid at room temperature.

This substance is an ionic solid. 

Explain why the physical properties of carbon dioxide are different from those of diamond and silicon(IV) oxide.

Germanium is an element in Group IV. The electron distribution of a germanium atom is 2 + 8 + 18 + 4. It has oxidation states of +2 and +4.

Germanium forms a series of saturated hydrides similar to the alkanes.

i) Draw the structural formula of the hydride which contains three germanium atoms per molecule.

[1]

ii) Predict the general formula of the germanium hydrides.

[1]

Draw a diagram showing the arrangement of the valency electrons in one molecule of the covalent compound germanium(IV) chloride, GeCl₄.

Use o to represent an electron from a chlorine atom.
Use x to represent an electron from a germanium atom.

The first three elements in Group IV are carbon, silicon and germanium. The elements and their compounds have similar properties.

The compound, silicon carbide, has a macromolecular structure similar to that of diamond. 

i) A major use of silicon carbide is to reinforce aluminium alloys which are used in the construction of spacecraft. Suggest three of its physical properties.

[3]

ii) Complete the following description of the structure of silicon carbide.

Each carbon atom is bonded to four ................................. atoms. Each silicon atom is bonded to ................................. carbon atoms.

[2]

Germanium forms a series of hydrides comparable to the alkanes.

i) Draw the structural formula of the hydride which contains four germanium atoms per molecule.

[1]

ii) Predict the products of the complete combustion of this hydride.

[2]

The properties of five alkenes at room temperature are shown in Table 1.1

Table 1.1

Answer this question using only the information in the table.

Suggest why the densities of the first three alkenes are much lower than the density of pentene and hexene.

The diagrams show part of the structures of five substances, A, B, C, D and E.

Answer the following question about these structures.

Which one of these structures, A, B, C, D or E, is used in cutting tools? 

Part of the structure of graphite is shown.

Use the information from the diagram to explain why graphite is used as a lubricant.

Carbon is an element which exists in different forms.

Name two forms of the element carbon that have giant covalent structures.

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Magnesium is a metal.

Describe the structure and bonding of metals. Include a labelled diagram in your answer.

In 1985 the fullerenes were discovered. They are solid forms of the element carbon. The structure of the C₆₀ fullerene is given below.

i) In the C₆₀ fullerene, how many other carbon atoms is each carbon atom bonded to?

 [1]

ii) Another fullerene has a relative molecular mass of 840.

How many carbon atoms are there in one molecule of this fullerene?

 [1]

Fullerenes are soluble in liquid hydrocarbons such as octane. The other solid forms of carbon are insoluble. Describe how you could obtain crystals of fullerenes from soot which is a mixture of fullerenes and other solid forms of carbon.

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A mixture of a fullerene and potassium is an excellent conductor of electricity.

i) Which other form of solid carbon is a good conductor of electricity?

 [1]

ii) Explain why metals, such as potassium, are good conductors of electricity.

 [2]

iii) The mixture of fullerene and potassium has to be stored out of contact with air. There are substances in unpolluted air which will react with potassium. Name two potassium compounds which could be formed when potassium is exposed to air.

[2]

It was reported from America that a turbine engine, the size of a button, might replace batteries. The engine would be built  from silicon which has suitable properties for this purpose.

The engine will run on a small pack of jet fuel. What other chemical is needed to burn this fuel?

Silicon has the same type of macromolecular structure as diamond.

i) Explain why one atom of either element can form four covalent bonds.

[2]

ii) Predict two physical properties of silicon.

[2]

iii) Name a different element that has a similar structure and properties to silicon.

[1]

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There are three types of giant structure – ionic, metallic and macromolecular.

Sodium nitride is an ionic compound. Draw a diagram that shows the formula of the compound, the charges on the ions and the arrangement of the valency electrons around the negative ion.

Use x to represent an electron from a sodium atom. Use o to represent an electron from a nitrogen atom.

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i) Describe metallic bonding.

[3]

ii) Use the above ideas to explain why:

metals are good conductors of electricity,
metals are malleable.

[3]

Carbon and silicon are elements in Group IV. Both elements have macromolecular structures.

Diamond and graphite are two forms of the element carbon.

i) Explain why diamond is a very hard substance.

[2]

ii) Give one use of diamond.

[1]

iii) Explain why graphite is a soft material.

[2]

iv) Give one use of graphite.

[1]

The first three elements in Group IV are

   Carbon

   Silicon

   Germanium

The element germanium has a diamond-type structure. Describe the structure of germanium. A diagram is acceptable.

Unlike diamond, graphite is soft and is a good conductor of electricity.

i) Explain why graphite has these properties.

[3] 

ii) Give a use of graphite that depends on one of these properties.

Property .................................

Use .................................

[1] 

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Lead is an excellent roofing material. It is malleable and resistant to corrosion. Lead rapidly becomes coated with basic lead carbonate which protects it from further corrosion.

Lead has a typical metallic structure which is a lattice of lead ions surrounded by a ‘sea’ of mobile electrons. This structure is held together by attractive forces called a metallic bond.

i) Explain why there are attractive forces in a metallic structure.

[2]

ii) Explain why a metal, such as lead, is malleable.

[2]

Basic lead(II) carbonate is heated in the apparatus shown below. Water and carbon dioxide are produced.

Silica gel absorbs water. Silica gel often contains anhydrous cobalt(II) chloride. When this absorbs water it changes from blue to pink. Suggest a reason.

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An ore of the important metal zinc is zinc blende, ZnS. This is changed into zinc oxide which is reduced to the impure metal by carbon reduction.

i) How is zinc oxide obtained from zinc sulfide?

[2]

ii) Write a balanced equation for the reduction of zinc oxide by carbon.

[1]

iii) The major impurity in the zinc is cadmium. The boiling point of zinc is 907°C and that of cadmium is 767 °C.

Name a technique which could be used to separate these two metals.

[2]

In common with most metals, zinc is a good conductor of electricity. It is used as an electrode in cells.

i) Give two other uses of zinc.

[2]

ii) Describe the metallic bonding in zinc and then explain why it is a good conductor of electricity.

[4]