GCSEScienceWJECScience (Double Award)ChemistryExam QuestionsChemical Bonding, Application Of Chemical Reactions & Organic ChemistryCrude Oil, Fuels & Organic Chemistry

Crude Oil, Fuels & Organic Chemistry (WJEC GCSE Science (Double Award): Chemistry): Exam Questions

Exam code: 3430

2 hours17 questions

6 marks

The structural formulae of seven organic compounds, A-G, are shown below.

Figure: Seven displayed structural formulae, labelled A to G. A: CH2=CH-CH2-CH3 (but-1-ene, 4 carbons, C=C between carbons 1 and 2). B: a central carbon bonded to four CH3 groups (above, below, left, right) — 2,2-dimethylpropane (neopentane), 5 carbons. C: a three-carbon chain with a CH3 branch on the middle carbon — 2-methylpropane (isobutane), 4 carbons, all single bonds. D: CH2=C(CH3)-CH3 (2-methylpropene, 4 carbons, C=C between carbons 1 and 2, with a methyl branch on carbon 2). E: a straight chain of 4 carbons, all single bonds — butane. F: a straight chain of 5 carbons with a C=C double bond between carbons 2 and 3 — pent-2-ene. G: a straight chain of 5 carbons, all single bonds — pentane

(i) Give the letters of the three compounds that have the general formula C_nH_2n.

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

[1]

(ii) State the number of compounds that are saturated.

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

[1]

(iii) Give the letter of the compound that is but-1-ene.

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

[1]

(iv) Draw the structural formula of the isomer of C₅H₁₂ not shown.

[1]

(v) Describe the chemical test that can be used to distinguish between compounds C and D.

Give the expected observation for both compounds.

[2]

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3 marks

The structural formula of vinyl chloride is shown below.

Figure: Displayed structural formula of vinyl chloride — two carbon atoms joined by a C=C double bond; the left carbon bonded to two H atoms, the right carbon bonded to one H atom and one Cl atom

Vinyl chloride can undergo a reaction known as polymerisation to produce polyvinyl chloride, commonly known as PVC.

Explain what happens to vinyl chloride molecules during the formation of PVC. Draw the repeating unit of PVC.

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1 mark

PVC is widely used in everyday life and has replaced many traditional materials.

Apart from cost, suggest two reasons why PVC has replaced iron for making drainpipes and guttering.

Reason 1 ....................................................................................

Reason 2 ...................................................................................

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6 marks

The diagram shows a fractionating column where crude oil is separated into simpler mixtures.

$Figure: Vertical fractionating column diagram. Crude oil enters near the bottom. Output pipes exit the column at different heights, from top to bottom: petroleum gases (very top), petrol, naphtha, kerosene, diesel oil, fuel oil (decreasing height down the column), and bitumen (bottom). Each pipe is labelled with the simpler mixture leaving the column at that point$

(i) Underline the correct word in the brackets to complete each sentence about the separation process.

I. Before the crude oil mixture enters the column it must be ( boiled / melted / filtered ).

[1]

II. Inside the column, the simpler mixtures ( evaporate / condense / solidify ).

[1]

III. The simpler mixtures that leave the fractionating column are called ( monomers / polymers / fractions ).

[1]

IV. The reason the simpler mixtures are separated from one another is that they have different ( masses / densities / boiling points ).

[1]

(ii) The table shows some information about the simpler mixtures obtained from crude oil.

Simpler mixture	Number of carbon atoms in the compounds	Use
petroleum gases	1–4	cooking
petrol	4–12	cars
naphtha	7–14	making chemicals
kerosene	11–15	aircraft
diesel oil	15–19	lorries
fuel oil	20–30	power stations
bitumen	more than 30	roads

I. Give the name of a mixture not used as a fuel.

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

[1]

II. Give the names of the two mixtures that contain compounds with 13 carbon atoms.

.............................................. and ............................................

[1]

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2 marks

One of the compounds found in petrol is octane, C₈H₁₈.

A_r(C) = 12

(i) Give the total relative mass of the carbon atoms in one molecule of octane.

Mass = .......................................................

[1]

(ii) The relative molecular mass of octane is 114. Use your answer to part (i) to calculate the percentage by mass of carbon in octane.

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

[1]

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3 marks

Fuel, heat and oxygen are the three factors needed to start and maintain a fire.

The photographs show three different methods used to put out fires or stop them from spreading.

Figure: Three photographs, each showing a different fire-fighting method. Photo 1 shows a cleared strip of land (a firebreak) cutting through a forest. Photo 2 shows a firefighter spraying a hose of water onto a large burning building. Photo 3 shows a woman in a kitchen smothering a small pan fire with a damp cloth.

(i) Draw one line from each method to the reason it puts out a fire.

[2]

(ii) Underline the type of fire that would be unsafe to put out using water.

bonfire electrical fire forest fire

[1]

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3 marks

The molecular formulae of five carbon compounds, A, B, C, D and E are shown below.

C₃H₆	C₂H₅OH	C₄H₈	C₂H₆	C₃H₈
A	B	C	D	E

(i) Alkanes are compounds with the general formula C_nH_2n+2.

Give the letters of the two compounds that are alkanes.

....................................................... and .......................................................

[1]

(ii) Give the name for compound A.

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

[1]

(iii) Draw the structural formula of compound E.

[1]

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4 marks

The following diagram shows two reactions of ethene.

Figure: Displayed structural formula of ethene (C=C double bond, each carbon bonded to two H atoms) with two reaction arrows leading from it: one labelled "orange bromine water, Br2" leading to a blank box labelled "molecule X" (showing a partial C-C single bond skeleton to be completed); another labelled "heat and catalyst" leading to a blank box labelled "repeating unit Y" (showing partial bracket ends with two dashes for bonds extending outward, to be completed)

(i) Complete the structural formulae for molecule X and repeating unit Y.

[2]

(ii) Describe the change that would be seen in the orange bromine water when molecule X is formed.

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

[1]

(iii) Name the type of reaction that takes place to form repeating unit Y.

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

[1]

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8 marks

Paper and plastic are both used to make disposable shopping bags.

Photograph comparing a brown paper shopping bag with handles on the left and a blue plastic carrier bag on the right.

The table compares the percentages of disposable paper and plastic bags used by consumers in a Welsh town between 1988 and 2018.

Type of bag	Percentage of disposable bags used (%)
Type of bag	1988	1993	1998	2003	2008	2013	2018
paper	73	63	31	12	8	13	21
plastic	27	37	69	88	92	87	79

(i) In 2003, the consumers of the town used a total of 1.25 million disposable bags.

Use the information in the table to calculate the number of paper bags used.

Number of paper bags = ....................................................... million

[2]

(ii) The graph below shows the percentage of paper bags used between 1988 and 2018.

Figure: Grid with x-axis "Year" showing 1988, 1993, 1998, 2003, 2008, 2013, 2018, and y-axis "Percentage of disposable bags used (%)" from 0 to 100 in steps of 10. A curve for paper bags is already plotted and drawn, passing through (1988, 73), (1993, 63), (1998, 31), (2003, 12), (2008, 8), (2013, 13), (2018, 21)

Plot on the same grid the percentage of plastic bags used between 1988 and 2018. Draw a suitable line.

[3]

(iii) Use the graph to answer the following questions.

I. Give the year when equal numbers of plastic bags and paper bags were used.

Year .......................................................

[1]

II. Circle the simplest ratio that compares the use of paper bags to plastic bags in 2000.

2 : 8 1 : 4 4 : 1 8 : 2 20 : 80

[1]

(iv) Give one reason that explains the change seen in plastic bag usage in Wales between 2008 and 2018.

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

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5 marks

Supermarkets across the UK now charge customers a minimum of 5p for every plastic carrier bag supplied.

Photograph of a person's hand carrying two white plastic carrier bags outdoors, with green foliage in the background

The reason for the charge is to reduce the number of plastic carrier bags used by consumers and therefore reduce waste and litter.

Since the introduction of the charge for plastic carrier bags in Wales, the number of these bags used by consumers has fallen by over 70%.

Similarly, reports in England claim that supermarkets have issued 83% fewer bags since the charge was introduced.

It is estimated that every person in the UK currently uses around 25 plastic carrier bags per year, compared to around 140 before charges were introduced.

The majority of the money retailers generate from sales of carrier bags is donated to good causes. A survey of retailers across England and Wales reported that £87 million had been donated to good causes since the introduction of the 5p charge, amounting to 4p for every bag sold.

(i) Use the information in the passage to decide whether the following statements are true or false.

Put a tick ( $✓$ ) in the correct column for each statement.

Statement	True	False
The number of plastic bags used in Wales and England has reduced since charging for them	$□$	$□$
Retailers donate all the money generated from the sale of plastic bags to good causes	$□$	$□$
Plastic bags are no longer used	$□$	$□$
The charge for plastic bags has totally stopped their use in Wales	$□$	$□$
The use of plastic bags leads to environmental problems	$□$	$□$
The charge for plastic bags is beneficial to good causes	$□$	$□$

(ii) How many fewer plastic bags will each person in the UK use over a 5-year period, based on the estimated number of bags used per person before and after the charge was introduced?

Number of bags = ................................................

[2]

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2 marks

More than half of all consumers still regularly buy plastic bags.

The pie chart shows the results of a survey where 100 consumers were asked what is the most they would pay for a plastic bag.

Give the number of consumers that would be prepared to pay more than 5p for a plastic bag.

Number of consumers = ................................................

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1 mark

Give one property of plastics which leads to long-term environmental problems.

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

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13a

1 mark

Saturated and Unsaturated Fats

Saturated and unsaturated fats are found in different amounts in different foods.

Unsaturated fats are often described as 'good fats'. When used to replace saturated fats in the diet they help lower cholesterol, one of the risk factors linked to heart disease.

While full-fat dairy products and meat contain large amounts of saturated fats, sources of unsaturated fats include nuts, seeds and vegetable oils.

Saturated and unsaturated fats differ in their chemical structures. Unsaturated fats contain double bonds between the carbon atoms within their molecular structure, whereas saturated fats have no double bonds.

The label on the bottle of a new brand of cooking oil claims that it is better than other cooking oils available on the market because it contains only 15% saturated fat. Scientists decided to investigate this claim.

They used bromine water to compare the percentage unsaturation of this new brand of cooking oil with four other vegetable oils, W, X, Y and Z. They also tested a known alkane and alkene.

They measured the volume of bromine water that could be added to each oil sample before the bromine water colour remained. Their results are shown below.

Sample	Mean volume of bromine water added (cm³)	Unsaturation (%)	Saturation (%)
oil W	20.4	50	50
oil X	12.0	30	70
oil Y	24.1	60	40
oil Z	16.3	40	60
new brand oil	30.1	?	?
alkane	0.1	-	-
alkene	40.0	-	-

Which one of these statements best describes the oils tested? Tick ( $✓$ ) the correct answer.

the oils contain saturated fats only	$□$
the oils contain unsaturated fats only	$□$
the oils contain both saturated and unsaturated fats	$□$
it is not possible to tell whether the oils contain saturated or unsaturated fats	$□$

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13b

2 marks

Explain why the first drops of bromine water that are added to each of the oil samples are decolourised.

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13c

3 marks

The label states that the new oil contains only 15% saturated fat. Use the results to show whether this statement is correct.

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13d

2 marks

Explain why these results might persuade many consumers to use this new brand of oil in preference to the other available brands.

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14a

2 marks

It is well known that plastic bags are a major source of litter. These bags can exist for a very long time, ranging from tens of years in the natural environment up to a thousand years in landfill.

The use of plastic bags is now banned in some countries. These countries commonly use bags made from paper or cotton, which do not cause the same litter problem as plastic bags.

Photograph of a large landfill site piled high with mixed rubbish, including extensive plastic waste. Birds fly above the waste and a muddy track runs through the foreground.

Paper or plastic?

Most people assume that a paper bag is better for the environment, however because paper bags are almost ten times heavier than plastic bags, they produce a greater mass of waste. On the other hand, because paper bags are biodegradable they do not lead to the same problem with litter as plastic bags.

When deciding whether paper is more suitable than plastic for making shopping bags, information from life cycle assessments (LCAs) of both materials must be taken into consideration.

Some of the findings from LCAs of paper and plastic bags are shown below.

Eight rounded text boxes present life-cycle assessment findings comparing paper and plastic bags, arranged in three rows: three boxes, three boxes, then two centred boxes.

On reading these findings it is important to consider all factors relating to sustainability when deciding on the most suitable material to make shopping bags. We should not just be thinking about what happens when we throw them away!

Use the information in the passage to compare the mass of waste and volume of litter generated from the use of plastic and paper bags.

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

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14b

3 marks

Use the information from the LCAs to tick ( $✓$ ) whether each of the factors supports or opposes the use of paper bags in preference to plastic bags.

Factor	Supports use of paper bags	Opposes use of paper bags
Impact of waste on marine life	$□$	$□$
Water consumption in production	$□$	$□$
Energy used in production	$□$	$□$
Carbon footprint generated in production	$□$	$□$
Energy used in recycling	$□$	$□$
Cost of transporting waste	$□$	$□$

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14c

1 mark

The use of which type of bag is more likely to be linked to the erosion of limestone buildings?

Give a reason for your answer.

Type of bag ...................................................................................

Reason ..........................................................................................

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Fire	Type of fire	Firefighting method	How method works
1	chip pan fire	tea towel	removes the heat
2	bonfire	fire blanket	removes the heat
3	electrical fire	fire breaks	removes the fuel

Time (hours)	Mass of bead (g)	Mass of water absorbed by bead (g) (to 1 decimal place)
0	0.035	0.0
2	4.048	4.0
4	6.030	6.0
6	7.280	7.2
8	7.891	7.9
10	8.181	8.1
12	8.181	8.1

Fire	Correction
1
2
3	Fire breaks are used to extinguish a forest fire

alkenes	$□$
monomers	$□$
polymers	$□$
alkanes	$□$