revision pack topic 7 – organic chemistry...revision pack topic 7 – organic chemistry topic...

Revision Pack Topic 7 – Organic Chemistry

Topic R/A/GCrude oil, hydrocarbons and alkanes Crude oil is a finite resource found in rocks. Crude oil is the remains of an ancient biomass consisting mainly of plankton that was buried in mud. Crude oil is a mixture of a very large number of compounds

Most of the compounds in crude oil are hydrocarbons, which are molecules made up of hydrogen and carbon atoms only

Most of the hydrocarbons in crude oil are hydrocarbons called alkanes. The general formula for the homologous series of alkanes is Cn H2n+2 The first four members of the alkanes are methane, ethane, propane and butane.

Alkane molecules can be represented in the following forms: C2H6 (molecular formula) or the displayed formula:

You should be able to recognise substances as alkanes given their formulae in these forms. You do not need to know the names of specific alkanes other than methane, ethane, propane and butane.

Fractional distillation and petrochemicals The many hydrocarbons in crude oil may be separated into fractions, each of which contains molecules with a similar number of carbon atoms, by fractional distillation

The fractions can be processed to produce fuels and feedstock for the petrochemical industry

Many of the fuels on which we depend for our modern lifestyle, such as petrol, diesel oil, kerosene, heavy fuel oil and liquefied petroleum gases, are produced from crude oil

Many useful materials on which modern life depends are produced by the petrochemical industry, such as solvents, lubricants, polymers, detergents

The vast array of natural and synthetic carbon compounds occur due to the ability of carbon atoms to form families of similar compounds

You should be able to explain how fractional distillation works in terms of evaporation and condensation. Remember, it is the relatively weak intermolecular forces between separate chains that are broken, not the strong internal covalent bonds in a molecule. Knowledge of the names of other specific fractions or fuels is not required

Revision Pack Topic 7 – Organic Chemistry Properties of hydrocarbons Some properties of hydrocarbons depend on the size of their molecules, including boiling point, viscosity and flammability. These properties influence how hydrocarbons are used as fuels

The boiling point (liquid to gas) and viscosity (thickness) increase with increasing number of carbons in a hydrocarbon chain. This is due to the increase in the strength of intermolecular forces between separate chains

The flammability (ability to burn the alkane) decreases with increasing molecular size, again due to an increase in the strength of intermolecular forces between separate chains

The combustion of hydrocarbon fuels releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised

The complete combustion of a hydrocarbon produces carbon dioxide and water. Students should be able to write balanced equations for the complete combustion of hydrocarbons with a given formula

Knowledge of trends in properties of hydrocarbons is limited to: • boiling points • viscosity • flammability

Cracking and alkenes Hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules

Cracking can be done by various methods including catalytic cracking and steam cracking. You should be able to describe in general terms the conditions used for catalytic cracking and steam cracking

The products of cracking include alkanes and another type of hydrocarbon called alkenes

Alkenes are more reactive than alkanes and react with bromine water, which is used as a test for alkenes. You should be able to recall the colour change when bromine water reacts with an alkene (red/brown to colourless – known as decolourisation of bromine water)

There is a high demand for fuels with small molecules and so some of the products of cracking are useful as fuels

Alkenes are used to produce polymers and as starting materials for the production of many other chemicals


Students should be able to balance chemical equations as examples of cracking given the formulae of the reactants and products e.g.

You should be able to give examples to illustrate the usefulness of cracking and also be able to explain how modern life depends on the uses of hydrocarbon (necessity of hydrocarbons as fuels)

Reactions of alkenes and alcohols (Chemistry only) Structure and formulae of alkenes Alkenes are hydrocarbons with a double carbon-carbon bond. The general formula for the homologous series of alkenes is Cn H2n

Alkene molecules are unsaturated because they contain two fewer hydrogen atoms than the alkane with the same number of carbon atoms

The first four members of the homologous series of alkenes are ethene, propene, butene and pentene

Alkene molecules can be represented in the following forms: C3H6 or:

Reactions of alkenes

Alkenes are hydrocarbons with the functional group C=C. It is the generality of reactions of functional groups that determine the reactions of organic compounds

Alkenes react with oxygen in combustion reactions in the same way as other hydrocarbons, but they tend to burn in air with smoky flames because of incomplete combustion

Alkenes react with hydrogen, water and the halogens, by the addition of atoms across the carbon-carbon double bond so that the double bond becomes a single carbon-carbon bond

Alkenes react with hydrogen, water and the halogens, by the addition of atoms across the carbon-carbon double bond so that the double bond becomes a single carbon-carbon bond

Revision Pack Topic 7 – Organic Chemistry Alcohols Alcohols contain the functional group –OH. Students should be able to recognise alcohols from their names or from given formulae

Methanol, ethanol, propanol and butanol are the first four members of a homologous series of alcohols. Alcohols can be represented in the following forms: CH3 CH2 OH or:

You should be able to: • describe what happens when any of the first four alcohols react with sodium, burn in air, are added to water, react with an oxidising agent • recall the main uses of these alcohols

Aqueous solutions of ethanol are produced when sugar solutions are fermented using yeast. You should know the conditions used for fermentation of sugar using yeast.

You do not need to know the names of individual alcohols other than methanol, ethanol, propanol and butanol. You are not expected to write balanced chemical equations for the reactions of alcohols other than for combustion reactions.

Carboxylic acids

Carboxylic acids have the functional group –COOH. Students should be able to recognise carboxylic acids from their names or from given formulae

The first four members of a homologous series of carboxylic acids are methanoic acid, ethanoic acid, propanoic acid and butanoic acid. The structures of carboxylic acids can be represented in the following forms: CH3COOH or:

Students should be able to: • describe what happens when any of the first four carboxylic acids react with carbonates, dissolve in water, react with alcohols • (HT only) explain why carboxylic acids are weak acids in terms of ionisation and pH (see Strong and weak acids (HT only))


Students do not need to know the names of individual carboxylic acids other than methanoic acid, ethanoic acid, propanoic acid and butanoic acid. Students are not expected to write balanced chemical equations for the reactions of carboxylic acids. Students do not need to know the names of esters other than ethyl ethanoate

Addition polymerisation

Alkenes can be used to make polymers such as poly(ethene) and poly(propene) by addition polymerisation.

In addition polymerisation reactions, many small molecules (monomers) join together to form very large molecules (polymers). For example:

In addition polymers the repeating unit has the same atoms as the monomer because no other molecule is formed in the reaction

You should be able to: • recognise addition polymers and monomers from diagrams in the forms shown and from the presence of the functional group C=C in the monomers • draw diagrams to represent the formation of a polymer from a given alkene monomer • relate the repeating unit to the monomer

Condensation polymerisation (HT only)

Condensation polymerisation involves monomers with two functional groups. When these types of monomers react they join together, usually losing small molecules such as water, and so the reactions are called condensation reactions

The simplest polymers are produced from two different monomers with two of the same functional groups on each monomer. For example:


You should be able to explain the basic principles of condensation polymerisation by reference to the functional groups in the monomers and the repeating units in the polymers

Amino acids (HT only)

Amino acids have two different functional groups in a molecule (an amine and a carboxylic acid end, where R can be anything):

Amino acids react by condensation polymerisation to produce polypeptides. For example: glycine is H2NCH2COOH and polymerises to produce the polypeptide (-HNCH2 COO-)n and n H2O Different amino acids can be combined in the same chain to produce proteins

DNA and other naturally occurring polymers DNA (deoxyribonucleic acid) is a large molecule essential for life. DNA encodes genetic instructions for the development and functioning of living organisms and viruses

Most DNA molecules are two polymer chains, made from four different monomers called nucleotides, in the form of a double helix

Other naturally occurring polymers important for life include proteins, starch and cellulose. You should be able to name the types of monomers from which these naturally occurring polymers are made


Task one

Task two


Task three

Define the following Organic Chemistry Key Words Alkene – Alkane – Saturated – Unsaturated – Hydrocarbon – Functional Group – Homologous Series Ethene – Propene – Butene – Pentene – Addition reaction – Hydration – Hydrogenation – Halogenation –


Define the following Key Words - answers Alkene – unsaturated hydrocarbon Alkane – saturated hydrocarbon Saturated – maximum number of hydrogens, no C=C Unsaturated – contains at least one C=C Hydrocarbon – molecule made of hydrogen and carbon only Functional Group – gives a family of organic compounds their characteristic reactions e.g. C=C Homologous Series – family of organic compounds with the same functional group e.g. alkene Ethene – alkene with 2 carbons Propene – alkene with 3 carbons Butene – alkene with 4 carbons Pentene – alkene with 5 carbons Addition reaction – molecule added across the double bond Hydration – addition of water (steam) Hydrogenation – addition of hydrogen Halogenation – addition of a halogen


Addition Reactions – Alkenes 1. Why can alkenes undergo addition reactions but alkanes cannot? (1 mark)

_______________________________________________________________________________________________ 2. Write the balanced equation for the reaction of propene and steam (2

marks)

_______________________________________________________________________________________________

3. Give the balanced symbol equation for complete combustion of butene (2

marks)

_______________________________________________________________________________________________ 4. Draw the displayed formula, showing all the bonds, and name the products

formed when: a. Propene reacts with iodine (2 marks)

b. Ethene reacts with steam (2 marks)

c. Butene reacts with chlorine (2 marks)

5. Explain why only one molecule of hydrogen is needed for every double bond

(2 marks)

Name:

Name:

Name:

Revision Pack Topic 7 – Organic Chemistry ___________________________________________________________

___________________________________________________________

________________________________________________________

6. Why do we react alkenes with hydrogen? What can hydrogenation be used to make? (2 marks)

___________________________________________________________

___________________________________________________________

________________________________________________________

Stretch 7. Draw the two products formed when pentene (with its double bond at the

end of the chain) reacts with steam. Explain why two products are formed (3 marks)

___________________________________________________________

___________________________________________________________

___________________________________________________________

_____________

Challenge 8. Using the slide on mechanisms, try and complete the mechanism for butene

(with the double bond in the middle of the chain) and chlorine. Then name the product, why is there only one product? (5 marks)


Alcohols – task Alcohols are a homologous series with the functional group –OH. One of the hydrogens on a carbon is replaced by –OH. Remember you have seen alcohols before in hydration of alkenes. In molecule: each carbon atom must form 4 bonds each hydrogen atom must form 1 bond each oxygen atom must form 2 bonds Using this information:

Make a model for each of the following alcohols using the moly mods Fill in the gaps in the table

Name Structural Formula Displayed Formula

Methanol CH3OH

Stretch: are alcohols hydrocarbons? Explain your answer Stretch: can you think of the link between the number of carbons, the number of hydrogens and number of oxygens? Put this together as a general formula Challenge: the last three alcohols can exist in different forms (called isomers). Draw one other form of each.


6 mark questions

Describe and evaluate the two methods for producing ethanol [6 marks] ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________

Describe the term homologous series and give examples and compare the structure of both alkanes and alkenes [6 marrks] ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________


Answers to 6 mark questions


Carbon compounds as fuels and feedback examination questions

Q1.This question is about hydrocarbons.

(a) The names and formulae of three hydrocarbons in the same homologous series are:

Ethane C2H6

Propane C3H8

Butane C4H10

The next member in the series is pentane.

What is the formula of pentane?

....................................................................................................................... (1)

(b) Which homologous series contains ethane, propane and butane?

Tick one box.

Alcohols

Alkanes

Alkenes

Carboxylic acids

(1)

(c) Propane (C3H8) is used as a fuel.

Complete the equation for the complete combustion of propane.

C3H8 + 5O2 → 3 .............................. + 4 ................................. (2)

(d) Octane (C8H18) is a hydrocarbon found in petrol.

Explain why octane is a hydrocarbon.


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

....................................................................................................................... (2)

(e) The table below gives information about the pollutants produced by cars using diesel or petrol as a fuel.

Fuel Relative amounts of pollutants

Oxides of Nitrogen

Particulate matter

Carbon dioxide

Diesel 31 100 85

Petrol 23 0 100

Compare the pollutants from cars using diesel with those from cars using petrol.

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

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

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

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

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

....................................................................................................................... (3)

(f) Pollutants cause environmental impacts.


Draw one line from each pollutant to the environmental impact caused by the pollutant.

Pollutant

Environmental impact caused

by the pollutant

Acid rain

Oxides of nitrogen

Flooding

Global

dimming

Particulate

matter

Global warming

Photosynthesis

(2) (Total 11 marks)

Q2.Plastic and glass can be used to make milk bottles.


The figure below shows the percentage of milk bottles made from glass between 1975 and 2010.

(a) Plot the points and draw a line on the figure above to show the percentage of milk bottles made from materials other than glass between 1975 and 2010.

(3)

(b) The table below gives information about milk bottles.


Glass milk bottle Plastic milk bottle

Raw materials Sand, limestone,

salt Crude oil

Bottle material Soda-lime glass HD poly(ethene)

Initial stage in production of bottle material

Limestone and saltused to produce

sodium carbonate.

Production of naphtha fraction.

Maximum temperature in production process

1600 °C 850 °C

Number of times bottle can be used for milk

25 1

Size(s) of bottle 0.5 dm3 0.5 dm3, 1 dm3, 2 dm3, 3 dm3

Percentage (%) of recycled material used in new bottles

50 % 10 %

Evaluate the production and use of bottles made from soda-lime glass and those made from HD poly(ethene).

Use the information given and your knowledge and understanding to justify your choice of material for milk bottles.

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

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

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

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

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

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

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

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

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(6)

(Total 9 mark

Revision Pack Topic 7 – Organic Chemistry Q3.Crude oil is a mixture of a very large number of compounds.

Figure 1 shows a laboratory experiment to separate crude oil.

Figure 1

(a) Complete the sentence.

The name for compounds that contain only hydrogen and

carbon is ...................................................................... . (1)

(b) Use the correct word from the box to complete each sentence.

condensation decomposition distillation evaporation reduction

(i) The process of separating crude oil is fractional ........................... . (1)

(ii) The process taking place at A is ............................................... . (1)

(iii) The process taking place at B is .............................................. . (10


(c) One of the compounds in crude oil is hexane. The displayed structure of hexane is shown in Figure 2.

Figure 2

Complete the sentences.

(i) Each line between the atoms in hexane represents a covalent ............................... .

(1)

(ii) Complete the chemical formula for hexane.

C6H............

(1)

(iii) Hexane can be broken down into smaller molecules by a process called

................................ . (1)

(d) Small molecules, called alkenes, are used to make polymers.

(i) Name the polymer made from butene.

............................................................................................................ . (1)

(ii) Incinerators are used to burn waste polymers, such as plastic bags.


Tick (✓) one advantage and tick (✓) one disadvantage of burning plastic bags.

Advantage

Tick (✓)

Disadvantage

Tick (✓)

Energy is released.

More recycling is needed.

Carbon dioxide is produced.

(2) (Total 10 marks)

Q4.A student investigated the viscosity of liquid hydrocarbons.

A viscous liquid is a liquid that flows slowly.

The student used this method.

• Measure 50 cm3 of the liquid hydrocarbon.

• Pour the liquid hydrocarbon into the funnel, as shown in Figure 1.

• Time how long it takes for all of the liquid hydrocarbon to run out of the funnel.

• Repeat the experiment for other liquid hydrocarbons.

(a) (i) Give the name of apparatus A in Figure 1.

.............................................................................................................. (1)


(ii) Name the apparatus that could be used to measure 50 cm3 of liquid hydrocarbon.

.............................................................................................................. (1)

(b) The student’s results for six liquid hydrocarbons are shown in Table 1.

Table 1

Formula of liquid hydrocarbon

Time for liquid hydrocarbon to run out of the funnel in seconds Mean time in

seconds Experiment 1 Experiment 2 Experiment 3

C5H12 12 11 13 12

C6H14 14 15 15 15

C7H16 19 20 18

C8H18 27 26 28 27

C10H22 46 48

47

C12H26 65 67 69 67

(i) The student did the experiment three times with each liquid hydrocarbon.

Give two reasons why. .......................................................................................................................

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

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

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

(2)


(ii) Use the data in Table 1 to calculate the mean time, in seconds, for C7H16

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

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

Mean time = ................................... seconds (1)

(iii) Complete the sentence.

As the number of carbon atoms in a molecule of liquid hydrocarbon increases, the time taken for the liquid hydrocarbon to run out of the funnel ................................................ .

(1)

(iv) A ring has been drawn around one result in Table 1.

This result has not been used to calculate the mean time for C10H22

Suggest why this result was not used.

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

.............................................................................................................. (1)

(v) Suggest one error the student may have made to get the ringed result.

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

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

.............................................................................................................. (1)


(c) The student investigated the effect of temperature on the viscosity of one of the liquid hydrocarbons.

The liquid hydrocarbon he was using had the hazard symbols shown in Figure 2.

(i) Suggest why the student warmed the liquid hydrocarbon using warm water and not a Bunsen flame.

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

.............................................................................................................. (1)

(ii) The student wore safety glasses.

Give one other safety precaution the student should take, and give a reason for this safety precaution.

Safety precaution .................................................................................

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

.............................................................................................................. (2)


(d) This is the method the student used to investigate the effect of temperature on the viscosity of one of the liquid hydrocarbons.

• Measure 50 cm3 of the liquid hydrocarbon and pour it into a beaker.

• Stand the beaker of liquid hydrocarbon in a heated water bath.

• Leave for a few minutes.

• Measure the temperature of the liquid hydrocarbon.

• Pour the liquid hydrocarbon into the funnel, as shown in Figure 3.

• Time how long it takes for all of the liquid hydrocarbon to run out of the funnel.

• Repeat the experiment at different temperatures.

(i) The student’s results are shown in Table 2.

Table 2

Temperature of liquid hydrocarbon in °C

Time to run out of the funnel in seconds

23 27

30 21

37 17

46 16

55 11

65 9


Plot the results shown in Table 2 on the graph in Figure 4.

Draw a curve of best fit.

(3)

(ii) One of the points is anomalous.

Draw a ring around the anomalous point on your graph. (1)

(iii) Predict how long it will take the liquid hydrocarbon to run through the funnel at 70 °C.

Show your working on your graph.

Time = ........................................ seconds (2)

(iv) Describe the relationship between the temperature of the liquid hydrocarbon and the viscosity of the liquid hydrocarbon.

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

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

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

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

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

.............................................................................................................. (3)


(v) The apparatus the student used in Figure 2 could lead to a systematic error in the results.

Identify one source of systematic error, and describe how the student could avoid or reduce the error.

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

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

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

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

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

.............................................................................................................. (2)

(Total 22 marks)

Q5.Crude oil is a fossil fuel.

(a) To make crude oil more useful it is separated into fractions.

Use the correct word from the box to complete each sentence.

boiling compound decomposition distillation

filtration mixture molecule

(i) Crude oil is a .................................................. of different substances. (1)

(ii) The substances in crude oil have different

.................................................. points. (1)

(iii) Crude oil is separated by fractional .................................................. . (1)


(b) Petrol is one of the fractions produced from crude oil.

Car engines use a mixture of petrol and air.

The diagram shows some of the gases produced.

(i) What type of reaction happens to petrol in a car engine?

Tick ( ) one box.

combustion

decomposition

neutralisation

(1)

(ii) Petrol contains octane (C8H18).

Complete the word equation for the reaction of octane with oxygen.

octane + ............................ ............................ + ............................ (2)

(iii) Cars use sulfur-free petrol as a fuel.


Describe why sulfur should be removed from petrol.

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

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

.

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

.

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

. (2)

(c) Some fractions from crude oil contain large hydrocarbon molecules.

These molecules can be cracked to produce smaller, more useful molecules.

An equation for cracking decane is:

C10H22 C3H8 + C2H4 + C5H10

decane propane ethene pentene

(i) Why is propane useful?

Tick ( ) one box.

Propane is a polymer.

Propane is an alloy.

Propane is a fuel.

(1)

(ii) Draw bonds to complete the displayed structure of ethene.


(1)

(iii) What is the colour change when bromine water reacts with ethene?

Tick ( ) one box.

Orange to colourless

Orange to green

Orange to red

(1)

(iv) Complete the sentence.

Pentene is useful because many pentene molecules can join together

to form .................................................. . (1)

(Total 12 marks)

Carbon compounds as fuels and feedback examination questions - answers


M1.(a) C5H12

1

(b) Alkanes 1

(c) (3) CO2

1

(4) H2O 1

allow for 1 mark

4 CO2 + 3 H2O

(d) contains hydrogen and carbon 1

(hydrogen and carbon) only 1

(e) (diesel) produces more oxides of nitrogen

allow converse answers in terms of petrol 1

produces (more) particulate matter 1

produces less carbon dioxide 1

(f)


2

[11]

M2.(a) all points correct

±1 small square

allow 1 mark for 6 or 7 plots 2

Year Percentage (%) ofbottles made from

other materials 1975 5 1980 10 1985 22 1990 42 1995 70 2000 72 2005 90 2010 95

1

(b) Level 3 (5–6 marks): A detailed and coherent argument is provided which considers a range of issues and comes to a conclusion consistent with the reasoning.

Level 2 (3–4 marks): An attempt to describe the advantages and disadvantages of the production and uses is made, which comes to a conclusion. The logic may be inconsistent at times but builds towards a coherent argument.


Level 1 (1–2 marks): Simple statements made. The logic may be unclear and the conclusion, if present, may not be consistent with the reasoning.

0 marks: No relevant content.

Indicative content

• glass – 2 stages in production of soda-lime glass • glass – second stage, heating sand, limestone and sodium

carbonate • HDPE – 3 stages in production • HDPE – second stage, cracking of naphtha to obtain ethene • HDPE – third stage, polymerisation of ethene • fewer stages in glass production, may be quicker • higher temperature in glass manufacture, therefore maybe

higher energy requirement • glass bottle can be reused • consideration of collection / cleaning costs to reuse glass

bottles • other glass products can be made from recycled glass • plastic has greater range of sizes • both produced from limited raw materials • higher percentage recycled materials in glass conserves raw

materials This indicative content is not exhaustive, other creditworthy responses should be awarded marks as appropriate.

6 [9]

M3.(a) hydrocarbons or hydrocarbon 1

(b) (i) distillation 1

(ii) evaporation 1

(iii) condensation 1


(c) (i) bond 1

(ii) (C6H)14

1

(iii) cracking 1

(d) (i) poly(butene)

allow with or without brackets 1

(ii) Advantage = energy is released

do not accept more than one tick in the advantage column

1

Disadvantage = carbon dioxide is produced

do not accept more than one tick in the disadvantage column

1 [10]

M4.(a) (i) (conical) flask 1

(ii) measuring cylinder / pipette / burette 1

(b) (i) any two from: • so anomalous results could be identified / ignored • so a mean / average could be taken • (to improve) accuracy

2


(ii) 19 1

(iii) increases / gets longer / gets bigger 1

(iv) anomalous / does not agree with other times for C10H22

1

(v) any one from: • shorter hydrocarbon used • volume of hydrocarbon too small • started timing late • stopped timing too early / when liquid left in funnel

must suggest why the result is lower than the others.

allow the temperature was higher or the students used a wider funnel.

1

(c) (i) flammable 1

(ii) suitable safety precaution 1

reason that links the safety precaution to the hazard symbols

eg:

• wear gloves

• (because) it is hazardous to health / harmful / toxic / irritant

or

• do not pour down sink or dispose of properly

• (because) it is harmful to the environment / kills fish

or

• wear a mask or do it in the fume cupboard or a well-ventilated area

• respiratory irritant 1

(d) (i) points plotted correctly (within half small square)

all six points correct scores 2

3, 4 or 5 points correct scores 1 2

smooth curve of best fit


1

(ii) point at 46 °C circled

allow point furthest from the line as drawn 1

(iii) working shown on graph 1

value read from graph line drawn (within half small square) 1

(iv) the higher the temperature the lower the viscosity

allow the higher the temperature the lower / shorter the time taken for 1 mark

2

non-linear or change gets smaller as temperature gets higher

answer relating temperature to time taken can score a maximum of 2 marks.

1

(v) identifying source of the error 1

method of avoiding the error

eg:

• the temperature will drop

• insulate the funnel

or

• runs out before all added

• put a tap on the funnel 1

[22]

M5.(a) (i) mixture (of different substances) 1

(ii) boiling (points) 1

(iii) distillation 1

(b) (i) combustion 1

(ii) (reactant)


oxygen

allow correct formulae 1

(products)

products in any order

carbon dioxide

allow carbon or carbon monoxide and water

allow water vapour or steam or hydrogen oxide 1

(iii) (burning sulfur) produces sulfur dioxide / S02

allow it / sulfur reacts with oxygen ignore sulfur oxide

1

causes acid rain 1

(c) (i) propane is a fuel 1

(ii) double bond drawn between carbon atoms

do not allow any other bonds or symbols 1

(iii) orange to colourless 1

(iv) poly(pentene)

allow polymer(s) 1

[12]

Synthetic and naturally occurring polymers questions

Q1.A molecule of ethene (C2H4) is represented as:

(a) A sample of ethene is shaken with bromine water.


Complete the sentence.

The bromine water turns from orange to ......................................................................... .

(1)

(b) Most ethene is produced by the process of cracking.

(i) Complete the sentence.

Cracking is a type of thermal .................................................................................. .

(1)

(ii) Decane (C10H22) can be cracked to produce ethene (C2H4) and one other product.

Complete the equation to show the formula of the other product.

C10H22 C2H4 + ......................... (1)

(c) Many molecules of ethene join together to produce poly(ethene).

(i) Complete the structure of the polymer in the equation.

(2)

(ii) Some carrier bags are made from poly(ethene). Some carrier bags are made from cornstarch.

Suggest two benefits of using cornstarch instead of poly(ethene) to make carrier bags.

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

.

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

.


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

.

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

. (2)

(Total 7 marks)

Q2. Modem window frames are often made from uPVC which contains the plastic poly(chloroethene).

Replace your old wooden windowswith our super high quality uPVC

windows!

(a) State why plastic window frames need no painting or maintenance.

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

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

(1)

(b) Poly(chloroethene) is a polymer formed by the addition polymerisation of chloroethene.

(i) Chloroethene is an unsaturated molecule. Why is this molecule said to be unsaturated?

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

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

(1)


(ii) Complete the diagram to represent how poly(chloroethene) is formed from chloroethene.

(3)

(iii) Explain what is meant by the term polymerisation.

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

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

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

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

(2)

(iv) Why is this an addition polymerisation?

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

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

(1) (Total 8 marks)

Q3. (a) Alkenes can be made by cracking large alkane molecules.

(i) Explain how the cracking process is carried out.

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

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

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


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

(2)

(ii) Give a chemical test which would show the difference between an alkene and an alkane.

Test ..................................................................................................................

Result of test ....................................................................................................

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

(2)

(b) Alkenes, such as ethene, can be made into polymers.

(i) Complete the following to show how the ethene molecules bond to form part of a polymer.

(1)

(ii) Name the polymer formed from ethene.

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


............ (1)

(iii) Explain one important problem caused by the everyday use of this polymer.

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

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

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

(2) (Total 8 marks)

Q4.Disposable nappies for babies need to absorb as much water as possible. Disposable nappies have a pad containing a special polymer called a hydrogel. Hydrogels absorb water.

A company called Aqanaps compared the water absorption of its nappy pads with nappy pads made by other companies.

• A scientist from Aqanaps poured 100 cm3 of water onto the pad of one of their nappies.

• He measured the volume of water that passed

through.

• He did the test three times using a new nappy pad for

each test.

• The scientist then repeated the procedure using the

nappy pads from three other companies, A, B and C.

The results are shown in the table.


Company

Volume of water collected in cm3

Pad 1 Pad 2 Pad 3

Aqanaps 55 57 55

A 47 46 39

B 65 63 64

C 38 39 38

(a) (i) Choose one result in the table that should be tested again.

Result: Company ............................ Pad ............................

Explain why you chose this result.

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

.

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

.

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

. (2)

(ii) Suggest one variable that should be controlled in this investigation.

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

.

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

. (1)

(iii) Suggest one possible cause of error in this investigation.

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

.

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

. (1)


(b) (i) The Aqanaps company studied the results. The company concluded that it should increase the amount of hydrogel used in its nappy pads.

Give two reasons why the company decided to increase the amount of hydrogel used in its nappy pads.

1 ............................................................................................................

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

.

2 ............................................................................................................

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

. (2)

(ii) Suggest one disadvantage for the company if it increases the amount of hydrogel used in its nappy pads.

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

.

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

. (1)

(Total 7 marks)

Q5. The raw materials used to make the polymer polyvinyl chloride (PVC) are crude oil and sea salt (sodium chloride).

(a) There are three main stages in the production of PVC.

(i) Stage 1 Cracking of hydrocarbons from crude oil produces ethene, C2H4

C10H22 C8H18 + C2H4

How are hydrocarbons cracked?

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

.


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

.

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

.

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

. (2)

(ii) Stage 2 Electrolysis of sodium chloride solution produces chlorine. Ethene from Stage 1 is then reacted with this chlorine. One of the hydrogen atoms in each ethene molecule is replaced by a chlorine atom to produce vinyl chloride.

Complete the chemical equation by writing in the formula of the product vinyl chloride.

C2H4 + Cl2 ........................................ +HCl

(1)

(iii) Stage 3 Polymerisation of vinyl chloride produces polyvinyl chloride (PVC).

Complete the chemical equation by drawing in the missing bonds of the product, PVC.

(1)

(b) Unplasticised polyvinyl chloride (uPVC) is used to make door and window frames. PVC with a plasticiser added is used to make cling film for wrapping food. A plasticiser is a chemical compound.

A student investigated how the percentage of plasticiser added to PVC affected its flexibility. The student measured the bending of PVC samples when a mass was


added.

The student’s results are shown in the table.

Sample of PVC

Percentage (%) of plasticiser

added

Bending of PVC sample in mm

Test 1 Test 2 Test 3 Test 4 Mean

A 0 2 3 3 4 3

B 5 22 15 23 24

C 10 27 27 29 29 28

D 15 34 35 35 36 35

(i) Each PVC sample should be the same size to make it a fair test. Explain why.

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

.

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

. (1)

(ii) The student repeated the test four times for each sample. Explain why.


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

.

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

. (1)

(iii) Calculate the mean value for sample B.

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

.

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

.

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

.

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

. (2)

(iv) Each of the samples bent the most in test 4. Suggest a possible reason for this.

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

.

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

. (1)

(c) Suggest why unplasticised polyvinyl chloride (uPVC) is used to make door and window frames.

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

.

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

. (1)

(Total 10 marks)


Synthetic and naturally occurring polymers questions - answers

M1.(a) colourless

ignore clear 1

(b) (i) decomposition 1

(ii) C8H18

1

(c) (i)

two single trailing bonds extending from the carbons (through the brackets) 1 mark

five single bonds (1 C–C bond and 4 C–H bonds) 1 mark

2

(ii) any two from:

• (polymers made from) cornstarch are biodegradable • less space needed in landfill sites • polymers from cornstarch come from a renewable source.

allow converse for poly(ethene) 2

[7]

M2. (a) not broken down by microorganisms or not bio-degradable

accept alternative answers such as:


do not rot / corrode / fade / react with atmosphere etc any answers which imply the inertness or non-biodegradability of this plastic accept they don’t react, they are ‘inert’ ignore rusting

do not accept weathering 1

(b) (i) (have a) double bond or do not have maximum number of (hydrogen) atoms attached

accept can add / react with hydrogen accept can take part addition reactions

do not accept it is a double bond do not accept additional reactions

do not accept has ‘spare’ / ‘free’ bond do not accept alkene alone

1

(ii) single bond between carbon atoms 1

all atoms correct + 2 ‘linking’ bonds (linking bonds need not go through bracket)

1

n moved to bottom right of bracket i.e. is below way on the right

first 2 marks are possible for chain structures

accept [– CHCl–CH2–] n

1

(iii) many molecules or many monomers 1

joined / bonded / linked or form long chain molecules / large molecules or to form a long chain polymer

accept many alkenes or many (ethene) molecules

do not accept many ethene alone etc.


to form a long polymer is not enough for 2nd mark 1

(iv) no other substances formed (A + B → C)

allow because double bond breaks so other atoms can add allow one product only

do not accept saturation occurs 1

[8]

M3. (a) (i) by heating

pressure is neutral

using a catalyst/pot/ceramic/porcelain/aluminium oxide 1

(ii) use bromine water/(alkaline) permanganate

accept bromine 1

alkene makes bromine go colourless or lose its colour

accept alkane does not change the red/orange colour of bromine

not change colour/goes clear 1

(b) (i)

either of these must show bonds at end 1

or


not H on ends

allow 3 instead of n not any other number

(ii) poly(ethene) – brackets not essential

accept polythene 1

(iii) large amount of waste polymer/poly(ethene)/polythene/litter

accept large amount of crude oil or finite resource used

1

it is not biodegradable

accept it does not

decompose/decay/break down

it causes pollution/it creates toxic

fumes when burnt are neutral

not it is not recyclable 2

[8]

M4.(a) (i) A and 3

accept A and 39 1

anomalous result

independent mark accept not close to other two volumes or correct comparison using the results

ignore does not fit the pattern 1


(ii) any one from:

• volume of water (used)

allow amount of water (used)

• time (for water to run through)

accept rate / speed (at which water runs through)

• temperature

• mass / surface area of pad

accept amount / size / volume / thickness of pad

• same filter funnel

ignore other equipment 1

(iii) any one from:

ignore human error unqualified

• incorrect / volume / amount of water added

• reading / volume / amount of water collected

• some water does not go through the pad

allow spillage / poorly placed pad

• not enough time allowed for water to drain through

accept rate / speed at which water is added

• pads (from one company) not identical / faulty 1

(b) (i) any two from:

• it was not the best (at absorbing the water)

accept correct descriptions of ‘not the best’ / third best or only better than B

• (needed) to absorb more (water)

allow not absorbing enough (water)

• to improve their image / sales

accept (needs) to absorb more (water) than A and C for 2 marks

2


(ii) any one from:

• cost (more)

• use (more) resources

• use (more) energy

must relate to the company 1

[7]

M5. (a) (i) if (fractional) distillation / hydrogenation mentioned as the method = max 1

heat / high temperature / hot / vaporise

allow thermal decomposition

ignore evaporation

do not accept ‘burns�

do not accept temperature < 100 1

catalyst or silica / alumina / porous pot

ignore other named catalyst

or steam

allow heat (the vapour) to a very high temperature / >800°C for 2 marks

1

(ii) C2H3Cl

ignore attempts to balance equation 1

(iii) single bonds between C – H, C – Cl and C – C

do not accept symbols outside the bracket 1


(b) (i) so that the amount of plasticiser / (sample of) PVC is the independent / only variable that affects the bending / flexibility of the samples

allow because different sizes would give different results

accept because size is a control variable

ignore references to reliability / precision etc 1

(ii) to improve the reliability (of the investigation)

accept to calculate a mean

accept to check for anomalous results or to check the range of results

ignore accuracy / precision etc 1

(iii) 23

correct answer with or without working = 2 marks

if answer is incorrect

allow

or 21 for 1 mark 2

(iv) (PVC) sample had been stretched / used / tested in first three tests

accept higher temperature

allow worn or become weaker

ignore (human) error

ignore more flexible / softer

ignore intermolecular forces 1

(c) does not bend (easily / much)

ignore non-biodegradable / low maintenance

or it is not flexible or it is rigid

ignore sturdy / stronger / harder 1

[10]

revision pack topic 7 – organic chemistry...revision pack topic 7 – organic chemistry topic...

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