Alkanes

Question 1

what is a catalytic converter

Answer 1

-device fitted in a car
-reduces amount of emissions from an internal combustion engine
-uses expensive metals like platinum and rhodium as the heterogeneous catalyst
-catalyst is mounted on a ceramic honeycomb to maximise the surface area

Question 2

Catalytic cracking

Answer 2

-type of cracking that takes place at:
-a slight pressure
-high temperature
-in the presence of a zeolite catalyst
-used mainly to produce motor fuels and aromatic hydrocarbons

Question 3

cracking

Answer 3

A process which involves breaking C-C bonds in alkanes to produce shorter chained alkanes and alkenes.

Question 4

thermal cracking

Answer 4

-type of cracking that takes place at a high pressure and high temperature
-produces a high percentage of alkenes

Question 5

difference between saturated and unsaturated

Answer 5

saturated: all the carbon-carbon bonds are single C-C bonds
unsaturated: have at least one double carbon bond (C=C)

Question 6

Compare catalytic and thermal cracking

Answer 6

Catalytic:
-uses zeolite catalyst, so faster rate contributes to it being cheaper
-high temperature (around 450 degrees), but lower than thermal so cheaper
-low pressure, so cheaper (not as high as thermal)
-produces alkanes and aromatic hydrocarbons

Thermal:
-high pressure (up to 7000kPa)
-produces mainly alkenes, which can be used to make polymers
-also produces some alkanes
-very high temperature (500-950 degrees)

Question 7

Steps of fractional distillation

Answer 7

-heat crude oil to a gas

-put gas in fractionating column, which has a temperature gradient – warmer at the bottom; cooler at the top

-the gases rise up the column, cool and condense at their boiling points

-the smaller the molecules are, the lower their boiling point, due to weaker Van der Waals forces between the molecules, so less energy is needed to separate them

-smaller molecules condense near the top of the column, where it is cooler

-the liquids are removed from the column as different fractions

-the smallest fractions are taken off at the top of the column as gases

-most of the shorter chains are used as fuels

-the longer chains are used as oil

Question 8

Order of fractions (top to bottom of fractionating column)
Remember: Real Guns Never Kill Deer by Firing Bananas

Viscosity ______ down the column

Flammability ______ down the column

Size of molecules ______ down the column

Boiling points ______ down the column

Answer 8

Shorter chain alkanes (refinery gases)
Petrol (used for cars)
Naphtha (used in cleaning products)
Kerosene (jet fuel)
Diesel (diesel engines)
Fuel oil (fuel for ships/factories)
Bitumen (contains paraffin wax and some other substances)

Viscosity increases down the column

Flammability decreases down the column

Size of molecules increases down the column

Boiling points increases down the column

Question 9

Explain why the sulfur compounds found in crude oil should be removed from the fractions before they are used for central heating fuel. (2 marks)

Answer 9

(On combustion) SO2 produced
Allow equation to produce SO2. Ignore sulfur oxides.

Which causes acid rain
If formula shown it must be correct
M2 is dependent on M1.
But if M1 is sulfur oxides, allow M2.
For M2 allow consequence of acid rain or SO2.
Ignore greenhouse effect and toxic

Question 10

Suggest one important substance manufactured on a large scale from propene (1 mark)

Answer 10

polypropene / propan(-1 or 2-)ol / propane(-1,2-)diol / isopropanol / propanone / propanal

Accept alternative names Ignore plastic and polymer

Question 11

Oxides of nitrogen are also produced during the combustion of paraffin in air.

Explain how these oxides of nitrogen are formed. (2 marks)

Answer 11

M1 Nitrogen and oxygen (from air) react / combine / allow a correct equation
If nitrogen from petrol / paraffin / impurities CE = 0 / 2.

M2 at high temperatures
Allow temperatures above 1000 °C or spark.
Not just heat or hot.
M2 dependent on M1.
But allow 1 mark for nitrogen and oxygen together at high temperatures.

Question 12

Write an equation to show how nitrogen monoxide in the air is converted into nitrogen dioxide. (1 mark)

Answer 12

2NO + O2 2NO2
Allow multiples.

Question 13

Nitric acid (HNO3) contributes to acidity in rainwater.
Deduce an equation to show how nitrogen dioxide reacts with oxygen and water to form nitric acid. (1 mark)

Answer 13

4NO2 + 2H2O + O2 —> 4HNO3

Question 14

Explain why the melting point of dodecane is higher than the melting point of the straight-chain alkane produced by cracking dodecane. (2 marks)

Answer 14

Larger molecule / longer carbon chain / more electrons / larger surface area

More / stronger van der Waals’ forces between molecules

Allow dispersion forces / London forces / temporary induced dipole-dipole forces between molecules.
If breaking bonds, CE = 0 / 2.

Question 15

Dodecane can be converted into halododecanes.
(2)
Deduce the formula of a substance that could be reacted with dodecane to produce 1-chlorododecane and hydrogen chloride only.

Answer 15

Cl2

Question 16

Pent-1-ene is a member of the alkene homologous series. Pent-1-ene can be separated from other alkenes.
State the physical property of alkenes that allows them to be separated from a mixture by fractional distillation. (1 mark)

Answer 16

(Different) boiling points
Ignore mp’s, references to imf, different volatilities

Question 17

The cracking of one molecule of compound X produces pent-1-ene, ethene and butane in a 1:2:1 mol ratio.
Deduce the molecular formula of X and state a use for the ethene formed. (2 marks)

Answer 17

C13H28

Making plastics/used to make polymers or polythene/used to make antifreeze/make ethanol/ripening fruit/any named additional polymer
not used as a plastic/polymer/antifreeze
not just ‘polymers’ – we need to see that they are being made

Question 18

State the type of cracking that produces a high proportion of ethene and propene.
Give the two conditions for this cracking process (2 marks)

Answer 18

Thermal (cracking)
If not thermal cracking CE = 0 / 2
High pressure AND high temperature
If blank mark on Allow high P and T

OR
Pressure of ≥ 10 atm, ≥ 1 MPa ≥ 1000 kPa
AND temp of 400 °C ≤ T ≤ 1000 °C or 650 K ≤ T≤ 1300 K
Do not allow high heat
If no units for T, then range must be 650 − 1000

Question 19

Outline the essential features of the fractional distillation of crude oil that enable the crude oil to be separated into fractions. (4 marks)

Answer 19

(1) Fractions or hydrocarbons or compounds have different boiling points/ separation depends on bp;
Ignore mp and vdw
(2) bp depends on size/ Mr/ chain length;
If refer to bond breaking/cracking/ blast furnace/oxygen/air 2
max
(3) Temp gradient in tower or column / cooler at top of column or vice versa;
QWC
(4) Higher bp / larger or heavier molecules at bottom (of column) or vice versa;
Not increasing size of fraction Not gases at top

Question 20

C8H18 is obtained by the catalytic cracking of suitable heavy fractions.
State what is meant by the term cracking and name the catalyst used in catalytic cracking.

Write an equation to show how one molecule of C14H30 is cracked to form one molecule of C8H18 and one molecule of another hydrocarbon.
Explain why oil companies need to crack ‘suitable heavy fractions’.
(4 marks)

Answer 20

Large molecules or compounds or long chain hydrocarbons (broken) into smaller molecules or compounds or smaller chain hydrocarbons;
QWC
Zeolite or aluminosilicate (catalyst);
C14H30 →C8H18 +C6H12;
Smaller chain molecules are in more demand or have higher value or vice versa;

Question 21

Write an equation for the incomplete combustion of C8H18 to form carbon monoxide and water only.
A catalytic converter is used to remove carbon monoxide from the exhaust gases in a car. Identify a catalyst used in the catalytic converter.
Write an equation to show how carbon monoxide is removed in a catalytic converter.
State why the water produced in the exhaust gases may contribute to global warming.
(4 marks)

Answer 21

C8H18 +81⁄2O2 →8CO+9H2O;
Allow multiples

Rh/ Pd/Pt/lr or in words;
Penalise contradiction of name and symbol
2CO+2NO→2CO2 +N2 / 2CO+O2 →2CO2;
Allow multiples
Greenhouse gas/ absorbs infrared radiation;

Question 22

When some petrol was accidentally contaminated in 2007, the sensors in the affected cars caused a decrease in the supply of petrol to the engine.
Suggest the effect that the contaminated fuel would have on the performance of the cars.
State how the oil company might have recognised the problem before the petrol was sold. (2 marks)

Answer 22

car less powerful/ car stops/ reduced performance/ won’t run smoothly/ can’t accelerate;
Not incomplete combustion or bad effect on engine. Not doesn’t go as far.
Test it (before sale) /Quality control etc;

Question 23

Crude oil is separated into fractions by fractional distillation. Outline how different fractions are obtained in this process (3 marks)

Answer 23

Crude oil is heated to vaporise it / oil vaporised (1)
(Vapour passed into fractionating) tower / column (1)
Top of tower cooler than bottom or negative temperature gradient (1)
fractions separated by b.p
OR condensed at different temperatures
OR levels
OR low boiling fractions at the top
OR at the top small molecules or light components (1)

Question 24

Give the two main types of product obtained by catalytic cracking. (2 marks)

Answer 24

Motor fuels
Aromatic hydrocarbons
Branched alkanes / hydrocarbons
Cycloalkanes

Any two (2)
Ignore specific fractions, alkanes, shorter alkanes, penalise alkenes, and hydrogen

Question 25

Name a catalyst used in catalytic cracking. State the type of mechanism involved and outline the industrial conditions used in the process. (4 marks)

Answer 25

Catalyst: Zeolite / aluminosilicate (1)

Type of mechanism: Carbocation / heterolytic fission (1)

Conditions: High temp OR around 450 °C [300 – 600] °C (1)
NOT heat / warm

Slight pressure [> 1 atm 10 atm OR 1 megaPa, 1000 kPa] (1)
NOT high pressure

Question 26

Gas oil (diesel), kerosine (paraffin), mineral oil (lubricating oil) and petrol (gasoline) are four of the five fractions obtained by the fractional distillation of crude oil within the temperature range 40–400 °C

Identify the missing fraction and state the order in which the five fractions are removed as the fractionating column is ascended. Give two reasons why the fractions collect at different levels in the fractionating column. (4 marks)

Answer 26

Missing fraction = naphtha (allow naphtha from list if not quoted separately) (1)
Order = mineral oil (lubricating oil), gas oil (diesel), kerosene (paraffin), naphtha, petrol (gasoline) (1)
Mark order consequential on M1 (if no missing fraction given, M2 = 0)
Accept correct reversed order

Negative temperature gradient on the column or temperature of column decreases upwards (1)

Larger molecules or heavier fractions condense at higher temperatures or lower down the column or reference to different boiling points (1)
(ignore mp)

Question 27

Explain why it is desirable that none of the sulphur-containing impurities naturally found in crude oil are present in petroleum fractions.

Answer 27

M1 Sulphur (containing impurities) burn to form or forms sulphur or oxides of sulphur
(if oxide identified, must be correct)
OR
equation: e.g. S+O2 →SO2 or H2S + 11⁄2 O2 → SO2 +H2O

M2 Leading to acid rain (must have specified oxides of S or burning) or toxic product or respiratory problems

Question 28

The pollutant gas NO is found in the exhaust gases from petrol engines. Explain why NO is formed in petrol engines but is not readily formed when petrol burns in the open air.

Answer 28

NO formed by reaction between N2 and O2 from the air (1)
OR
N2 +O2 →2NO
High combustion temperature or spark in engine (1)
provides EA or sufficient heat / energy to break N-N triple bond (1)

Question 29

The pollutant gas CO is also found in the exhaust gases from petrol engines. Explain how CO and NO are removed from the exhaust gases and why the removal of each of them is desirable.

Answer 29

Need to remove NO as forms acid rain or toxic product or causes respiratory problems (1)
2NO + O2 → 2NO2 (1)
4NO2 + O2 + 2H2O → 4HNO3 (1)
Need to remove CO as it is poisonous (1)
Catalytic converter (1)
uses Pt / Rh / Pd / Ir (wrong answer cancels a correct one) (1)
Provides active sites / reduces EA (1)
Forms N2 +CO2 (1)
2NO+2CO→N2 +2CO2 (correct equation worth last 2 marks) (1)

Question 30

Give examples of ozone depletion equations

Answer 30

Cl* + O3 → ClO* + O2
ClO* + O3 → 2O2 + Cl*

Question 31

Why is ozone beneficial

Answer 31

Absorbs UV before it reaches Earth

Question 32

Why do chlorine atoms form in the upper atmosphere

Answer 32

Chlorine atoms are formed in the upper atmosphere when ultraviolet radiation causes C–Cl bonds in chlorofluorocarbons (CFCs) to break.

Question 33

Impact of chlorine on ozone depletion

Answer 33

catalyse the decomposition of ozone and contribute to the hole in the ozone layer.