GCSEScienceWJECScience (Double Award)ChemistryExam QuestionsChemical Bonding, Application Of Chemical Reactions & Organic ChemistryBonding, Structure & Properties

Bonding, Structure & Properties (WJEC GCSE Science (Double Award): Chemistry): Exam Questions

Exam code: 3430

2 hours16 questions

3 marks

(i) The box below contains the names of some common types of smart material.

photochromic pigment hydrogel shape memory alloy
shape memory polymer thermochromic pigment

Choose from the box the type of smart material that is used in:

I. disposable nappies,

..........................................................................................................................................

[1]

II. lenses for sunglasses.

..........................................................................................................................................

[1]

(ii) What must be done to a thermochromic pigment for it to change colour?

Tick (✓) the box next to the correct answer.

heat it	$□$
add water	$□$
place it in sunlight	$□$

[1]

How did you do?

4 marks

The following diagram shows a giant ionic structure.

Figure: Close-packed 3D structure of a giant ionic lattice, showing alternating positive and negative ions (green and yellow spheres) regularly arranged and closely packed together

Giant ionic structures have high melting points and conduct electricity when dissolved or molten.

(i) Use the diagram and your knowledge to draw one line from each property to its correct explanation.

Figure: A matching exercise — two property boxes on the left ("high melting point", "conducts electricity when dissolved or molten") to be linked by drawn lines to four explanation boxes on the right ("ions are regularly arranged", "strong bonds between ions", "ions are free to move", "ions cannot move")

[2]

(ii) The following diagram shows a simple covalent structure.

Figure: Four separate small covalent molecules (each with one central red atom double-bonded to two grey/white atoms, similar to CO2), scattered apart from each other with gaps between them, showing weak forces between separate molecules

Simple covalent structures have low melting points and do not conduct electricity.

Use the diagram and your knowledge to draw one line from each property to its correct explanation.

Figure: A matching exercise — two property boxes on the left ("low melting point", "does not conduct electricity") to be linked by drawn lines to five explanation boxes on the right ("strong forces between molecules", "molecules cannot move", "weak forces between molecules", "molecules are not charged", "molecules are tightly packed")

[2]

How did you do?

2 marks

Diamond and graphite have giant covalent structures. Diamond is commonly used in drill tips, whereas graphite is used in pencils.

Figure: Two photographs side by side — drill tips coated with diamond grit, and a row of sharpened pencils

Use your knowledge of the properties of diamond and graphite to underline the correct word in the brackets to complete each sentence.

Diamond is used in drill tips because it is ( hard / soft / malleable ) and has a high melting point.

Graphite is used in pencils because the layers of atoms are held together weakly and are able to slide ( through / into / over ) each other.

How did you do?

Was this exam question helpful?

10a

2 marks

In 1985, a new allotrope of carbon was discovered and named buckminsterfullerene. This allotrope consists of sixty carbon atoms joined together to resemble a shape similar to that of a football (Figure 1), only ten septillion (10,000,000,000,000,000,000,000,000) times smaller.

This form of carbon was named after the architect Buckminster Fuller, famous for designing geodesic domes, as shown in Figure 2.

Figure: Figure 1 shows a ball-and-stick or space-filling model of buckminsterfullerene (C60), a spherical cage of 60 carbon atoms resembling a football pattern of hexagons and pentagons, labelled with a diameter of 1.1 nm. Figure 2 shows a geodesic dome building, a spherical lattice structure of triangular/hexagonal panels, illustrating the architectural inspiration for the molecule's name.

The structure of buckminsterfullerene is a truncated icosahedron, consisting of 20 hexagons and 12 pentagons that intersperse to form a spherical structure. Within the structure, each carbon atom is bonded to three other carbon atoms and no pentagon has a joining edge with another pentagon.

Other spherical allotropes of carbon, called fullerenes, have since been made. These include balls consisting of seventy, seventy-six and eighty-four carbon atoms. Together, they have become known as 'Buckyballs'.

Fullerenes have high melting points and boiling points. They also have a high density and a large surface area for their size.

Today, fullerenes are at the heart of nanotechnology – the study of atomic scale structures and devices. This provides many exciting new research possibilities for scientists including their potential uses in catalysts, lubricants and in nano-tubes for strengthening materials and as a way of delivering drugs into the body.

Nano-tubes are fullerenes that are used to reinforce graphite in tennis rackets because they are very strong. They are also used as semiconductors in electrical circuits.

The nano-tube's structure also allows it to be used as a container for transporting a drug in the body. A molecule of the drug can be placed inside the nano-tube cage. This keeps the drug 'wrapped up' until it reaches the site where it is needed. In this way, a dose that might be damaging to other parts of the body can be delivered safely to, for example, a tumour.

Tick ( $✓$ ) all the statements that correctly describe buckminsterfullerene.

its structure has 32 faces	$□$
it has a relative molecular mass of 60	$□$
it is an allotrope of carbon	$□$
it has a giant ionic structure	$□$
it is a hydrocarbon compound	$□$
it is a smart material	$□$
it is $1 \times 10^{25}$ times smaller than a football	$□$

How did you do?

10b

5 marks

(i) Use the following formula to calculate the number of edges that a molecule of buckminsterfullerene has.

$number of edges = \frac{total number of sides of all pentagons and hexagons}{2}$

Number of edges = ..........................................

[2]

(ii) Calculate, in m³, the approximate volume of a buckminsterfullerene molecule.

Write your answer to three significant figures and in standard form.

$Volume = \frac{4}{3} π r^{3}$

$π = 3.14 r = radius 1 nm = 1 \times 10^{- 9} m$

Volume = ............................................... m³

How did you do?

10c

1 mark

Give the main reason why the structure of fullerenes has resulted in there being an interest in developing their use as catalysts.

How did you do?

10d

1 mark

State why some people might oppose the use of fullerenes in drug delivery systems in the body.

How did you do?

10e

2 marks

One student said that Buckyballs should be good electrical conductors but her friend disagreed.

Use your knowledge of bonding and structure to give one reason that each student could use to support their argument.

How did you do?

Was this exam question helpful?

11a

1 mark

Hydrogels are macromolecules, meaning they contain very large numbers of atoms.

Photograph of two hands cupping a handful of small, translucent hydrogel beads in red, blue, green, yellow and purple, with many more colourful beads scattered across the background.

They are polymers made from hydrophilic polymer chains. This means that they readily mix with water.

Cross-links between the polymer chains enable hydrogels to form their three-dimensional shape.

The cross-links that join the individual polymer chains together are formed by small reactive molecules that contain one or more double bonds.

The interesting feature of hydrogels is their ability to swell and shrink, depending on their surroundings. When in contact with water, hydrogels are able to absorb water and swell to many times their original size and weight, whilst maintaining the same shape.

Being able to absorb water like this has enabled hydrogels to be used in a wide range of applications. For many of these applications it is important to understand how the properties of hydrogels change with temperature.

Table 1 and Table 2 show how temperature affects the properties of hydrogel beads in water over time.

Table 1 — the effect of temperature on the mass of hydrogel beads

Time (hours)	Mass of bead (g)
Time (hours)	10 °C	20 °C	40 °C
0	0.035	0.035	0.035
2	1.305	2.980	4.280
4	2.512	3.681	5.904
6	3.613	4.389	6.760
8	4.298	5.195	8.101
10	5.120	5.572	8.101
12	5.400	5.980	8.101

Table 2 — the effect of temperature on the diameter of hydrogel beads

Time (hours)	Diameter of bead (mm)
Time (hours)	10 °C	20 °C	40 °C
0	3.56	3.56	3.56
2	10.30	13.00	18.10
4	13.40	16.50	21.70
6	16.20	18.50	23.60
8	17.80	19.60	25.24
10	19.50	20.80	25.24
12	20.50	22.00	25.24

Tick (✓) the statement that best describes the molecules that form the cross-links within hydrogels.

they are macromolecules	$□$
they are unsaturated	$□$
they contain hydrophilic groups	$□$
they are polymers	$□$

How did you do?

11b

1 mark

Give the phrase in the passage that shows the change the hydrogel undergoes is a physical rather than a chemical change.

How did you do?

11c

2 marks

Calculate the percentage increase in mass of a hydrogel bead when placed in water at 20 °C for 6 hours.

Percentage increase = ........................................................ %

How did you do?

11d

2 marks

Write a conclusion for the effect of temperature on the diameter of hydrogel beads in water over time.

How did you do?

Was this exam question helpful?

Ionic compound	Ions present
potassium chloride	potassium and chloride
calcium oxide	calcium and oxide

Ion	Number of protons	Number of electrons
Ca²⁺	.......................................	.......................................
Br^-	.......................................	.......................................

Element	Electronic structure
carbon	2,4
hydrogen	1

Element	Electronic structure
sodium	2,8,1
oxygen	2,6

Element	Electronic structure
carbon	2,4
hydrogen	1

Substance	Melting point (°C)	Electrical conductivity	Type of structure
A	2072	conducts only when molten	.................................................................
B	-182	does not conduct electricity	.................................................................
C	1610	does not conduct electricity	.................................................................

Substance	Melting point (°C)
sodium chloride	801
magnesium oxide	2852

Ion	Charge	Electronic structure
magnesium	+2	...............................
chloride	............................	2,8,8