Revision Pack Topic 7 – Organic Chemistry Topic R/A/G Crude 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
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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
Revision Pack Topic 7 – Organic Chemistry
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))
Revision Pack Topic 7 – Organic Chemistry
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:
Revision Pack Topic 7 – Organic Chemistry
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
Revision Pack Topic 7 – Organic Chemistry
Task one
Task two
Revision Pack Topic 7 – Organic Chemistry
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 –
Revision Pack Topic 7 – Organic Chemistry
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
Revision Pack Topic 7 – Organic Chemistry
Revision Pack Topic 7 – Organic Chemistry
Revision Pack Topic 7 – Organic Chemistry
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
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
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)
Revision Pack Topic 7 – Organic Chemistry
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.
Revision Pack Topic 7 – Organic Chemistry
Revision Pack Topic 7 – Organic Chemistry
Revision Pack Topic 7 – Organic Chemistry
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] ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________ ___________________________________________________________
Revision Pack Topic 7 – Organic Chemistry
Answers to 6 mark questions
Revision Pack Topic 7 – Organic Chemistry
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:
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.
Revision Pack Topic 7 – Organic Chemistry
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.
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
(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.
Revision Pack Topic 7 – Organic Chemistry
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
Revision Pack Topic 7 – Organic Chemistry
(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
Revision Pack Topic 7 – Organic Chemistry
(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
Revision Pack Topic 7 – Organic Chemistry
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.
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.
Revision Pack Topic 7 – Organic Chemistry
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 ............................
(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.
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
Revision Pack Topic 7 – Organic Chemistry
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.
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:
Revision Pack Topic 7 – Organic Chemistry
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.
Revision Pack Topic 7 – Organic Chemistry
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
Revision Pack Topic 7 – Organic Chemistry
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
Revision Pack Topic 7 – Organic Chemistry
(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
Revision Pack Topic 7 – Organic Chemistry
(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
Revision Pack Topic 7 – Organic Chemistry
(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