F332 Blue Book questions

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Question 1

Give two reasons why bromine is dangerous if spilt while being transported. [2]

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Answer 1

toxic (vapour)/ respiratory problems (1); corrosive/ dangerous to/blisters/damages skin (1)

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Question 2

In the event of an accident when chlorine is being transported, people living near the accident site are evacuated. What properties of chlorine make this necessary? [2]

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Answer 2

Volatile / gas (1); toxic (to humans) / causes respiratory diseases / choking gas (1).

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Question 3

Suggest what is meant by the term oxidant [1]

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Answer 3

Chemical that: causes another chemical to be oxidised / is itself reduced / decreases in oxidation state / is an electron acceptor / removes electrons from another chemical (1)

allow ‘chemical that oxidises another chemical’ / oxidising agent.

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Question 4

Explain the benefits and disadvantages of using chlorine to treat drinking water. Include references to the transport and storage of chlorine. [5]

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Answer 4

Any five points from:

 1.      kills bacteria / kills pathogens / disinfectant (1)

2.      cheap compared to other water treatment chemicals. (1 do not allow just ‘cheap’.

3.      Cl2 or chlorine is a gas, making it difficult to contain / it spreads easily. (1)

Answer must have ‘gas’ and either ‘difficult to contain’ or ‘spreads easily’ to gain the mark.

4.      toxic / poisonous (1)

do not allow harmful / irritant / dangerous instead of toxic.

5.      causes respiratory problems / breathing problems (1)

7.      dissolves in rivers / local water supplies (1)

8.      forming bleach and acid (1)

9.      (bleach and acid) kill life forms in the water (1)

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Question 5

The reactivities of the elements of Group 2 are related to their ionisation enthalpies.

(i)      Calcium has lower first and second ionisation enthalpies than magnesium.

          Explain why this is so.

          How does the difference in ionisation enthalpies of calcium and magnesium affect the relative ease of ion formation and the reactivities of the elements? [4]

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Answer 5

(i)      Four from
SIZE: Calcium / “It” has larger atom / more electron shells / electrons
further from nucleus (1);
ATTRACTION: electron(s) held less tightly / more shielding /
less attraction to nucleus / protons (1);
EASE OF LOSS: electron(s) more easily lost / got rid of / ion
formed more easily / less energy needed to remove electron(s) ora (1)
REACTIVITY: more reactive ora (1);
Group 2 / Mg and Ca / Metals react by losing electrons (1)

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Question 6

Many properties such as first ionisation enthalpy vary in a regular way across a period.

Explain the general increase in first ionisation enthalpy as the Period 3 (sodium to argon) is crossed from left to right. [2]

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Answer 6

electrons in same shell/same no. of shells/rings (1); NOT energy level                     

nuclear charge bigger/greater nuclear/proton attraction/more protons/e’s held more tightly (1)

NOT more nucleons/magnetic attraction

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Question 7

In this question, one mark is available for the use and organisation of scientific terms.

          You are provided with 250 cm3 of clear rain water and 100 cm3 of 0.0050 mol dm–3 sodium hydroxide solution. You have access to normal laboratory apparatus and any other chemicals you require.

          Describe how you would carry out a titration to find the acidity (concentration of hydrogen ions) of the rain water. These solutions do not need diluting. [6]

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Answer 7

Pipette NaOH into flask (1);
fill burette with rain water (1);
add indicator (1);
(at end point) add rain water dropwise / slowly (1);
repeat to get concordant readings AW (1).
If NaOH & rain water reversed then allow 1 mark, hence max of 4.

1 mark for two sentences / 2 bullet points including correct use of two
of the following words:
pipette, burette, indicator, concordant, end-point.

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Question 8 (links to 7)

Write an ionic equation for the reaction of the acidic solution with hydroxide ions. Give state symbols.


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Answer 8

H+(aq) + OH(aq) à H2O(l)
OH (1); rest correct (1); state symbols correct (1).

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Question 9

Explain, in terms of intermolecular bonds, why chlorine is a gas at room temperature and pressure but bromine is a liquid under the same conditions. As part of your answer, you should explain how the intermolecular bonds arise. [5]

          In your answer, you should use appropriate technical terms, spelt correctly.

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Answer 9

must have:

          1. instantaneous (dipole) – induced dipole bonds (underlined part must be correctly spelt) (1);

          plus four out of:

          2. electron movements in the molecules create an uneven distribution of charge (1);

          3. a dipole is induced in a neighbouring molecule leading to attraction (1);

          4. intermolecular bonds are stronger in bromine/Br2 ORA(1);

          5. bromine has more electrons (ORA) (1);

          6. more energy / higher temperature is needed to break intermolecular bonds in bromine ORA (1);

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Question 10

Explain instantaneous dipole-induced dipole forces of attraction.

          In your answer you should refer to:

        how instantaneous dipole–induced dipole forces arise;

        how these forces can be used to account for the higher boiling point of straight chain hydrocarbons compared to that of branched chain hydrocarbons. [6]

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Answer 10

5 from:                                                                                                                                   

  • A Electron movements (1) stated or implied
  • B in the molecules create an uneven distribution of charge, leading to
  •           a temporary/instantaneous dipole (1);
  • C The temporary/instantaneous dipole in one molecule
  •           creates/induces a dipole in a neighbouring molecule, then attracts it (1);
  • D straight chain molecules have stronger * instantaneous dipole – induced dipole forces (1)
  • E This allows greater surface contact/molecules closer together and
  •           stronger * intermolecular forces between straight chain molecules (1);
  • F Stronger * intermolecular forces mean that more energy is needed to
  •           overcome them/ harder to break, therefore higher b.p. (1);
  •  * allow “more” or “greater”. Allow “intermolecular bonds”                                     1
  • And QWC: Logical, correct use in context of at least three terms below:
  • dipole * ; electron; intermolecular; charge; induces * ; molecule, branches
  •  * but not in “instantaneous dipole- induced dipole”


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Question 11

When bromomethane, CH3Br, is bubbled through aqueous silver nitrate a precipitate of silver bromide forms slowly.

(i)      The first reaction to occur is the hydrolysis of bromomethane by the water present. Write an equation for this reaction. [2]

(ii)     The bromomethane molecule has a polar bond. Explain the meaning of the term polar and how this is linked to the electronegativities of the atoms involved. Draw a diagram to illustrate the polar bond in bromomethane. [3]

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Answer 11

(i)         CH3Br + H2O (1) → CH3OH + HBr (1) ignore state symbols

(ii)        carbon is δ+, bromine δ– (1) (in diagram)
polar means electrons shared unequally in the bond/ one atom has
a partial positive charge, other partial negative (1)
partial only needs to be mentioned once
bromine has a greater electronegativity than carbon (ora)/ atoms
forming bond have different electronegativities (1);

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Question 12

Scientists monitor the composition of the Earth’s atmosphere. They have found that the concentration of carbon dioxide in dry, unpolluted tropospheric air has increased from 300 ppm to around 380 ppm between 1900 and the present day.

(ii)     Carbon dioxide is described as a ‘greenhouse gas’. Greenhouse gases absorb infrared radiation in the troposphere.

          Explain the source of the infrared radiation absorbed by carbon dioxide and the possible link between increased concentrations of carbon dioxide in the troposphere and global warming. [6]

 In your answer, you should make it clear how the steps you describe are linked to one another.  

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Answer 12

(ii)     Any four points from:
1       Sun emits UV (1) - ignore other types of radiation from the Sun.
2       Earth absorbs some of the energy (from the Sun) /heats up (1)
3       Earth radiates emits / re-emits IR (1) - do not allow Earth reflects IR in point 3.
4       (CO2) absorbs IR radiation (1)
5       making bonds vibrate (more) (1) (Award marks for points 5 and 6 if the wrong frequency range of radiation is given as being absorbed in 4. (eg candidate states CO2 absorbs UV).)
6       turned into kinetic energy that raises the temperature /transfers kinetic energy to thermal energy or heat or it warms the atmosphere or Earth. (1)
7       some CO2 molecules radiate IR (which warms Earth) (1) AND more CO2 molecules means more radiation is absorbed / more COmeans greater temperature increase / enhancing the greenhouse
effect / causing global warming / warming the atmosphere / Earth / planet more (1)
          QWC mark for connection of ideas: idea of linking IR absorbtion to vibrations of bonds / increase in temperature 

 (marking point 4 linked to 5 or 6) (1)

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Question 13

13.     Chlorine atoms in the upper atmosphere catalyse the breakdown of ozone.

(i)      Complete the equations below to illustrate this. [2]

                             Cl      +       O3    ®           +

                                      +                ®     Cl   +      O2

(ii)     How can you tell from the equations in (i) that chlorine atoms are catalysts for the breakdown of ozone? Why is the process faster in the presence of a catalyst? [2]

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Answer 13

(i)         ClO + O2 (1); ClO + O (1) IGNORE dots         

(ii)     They are recycled/not used up/remain unchanged (AW) (1);
Catalysts provide a route with lower activation enthalpy/energy
(accept; They lower the activation e.) (1)                                                 


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Question 14

Hydrofluorocarbons, HFCs, are now being used to replace CFCs for many of their uses. They are broken down in the troposphere before they have time to reach the stratosphere. Their disadvantage is that they are greenhouse gases.

 (i)     CFCs were once widely used. Give two of their uses and two of their properties. [4]

(ii)     CFCs cause depletion of the ozone layer. Describe how they do this. [5]

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Answer 14

(i)      two from:                                                                                                            

          aerosol (propellants); blowing agents; cleaning agents; refrigerants (aw);
coolant in air conditioning units; fire extinguishers (2)

            High heat of vaporisation/volatile/non-toxic/unreactive (2)

(ii)     in the stratosphere/upper atmosphere (1);

High energy uv light (1);

homolytic fission (1);

chlorine radicals/ Cl (1);

these catalyse the breakdown of ozone (1)                                                         

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Question 15 a

(a)     Bromomethane and chloromethane are both present in the atmosphere. Explain how chloromethane causes ozone depletion in the stratosphere and suggest why bromomethane has a lower ozone depleting potential than chloromethane. [5]

  In your answer, you should use appropriate technical terms, spelled correctly.

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Answer 15 a

(a)     Any two from:

1.      chloromethane is not broken down / unreactive in the troposphere / lower atmosphere (1)

2.      but is broken down / photodissociated (in the stratosphere) /
AW by (1)

3.      high energy UV / high frequency UV (1) (allow ‘radiation’ for ‘UV’)

4.      (breakdown of chloromethane) producing chlorine atoms /
chlorine radicals (1)              (
Points 2 and 4 can be scored from a reaction equation.)

          AND   (products of chloromethane) catalyse ozone breakdown / AW (1)

QWC: To gain this mark, candidate must use the word catalyst or a derivative of it, spelled correctly and used in a grammatically correct way (eg: do not award for ‘it catalyse the breakdown of ozone’). allow ‘catalyze’.

C–Br bond is weaker (than C–Cl) OR so can be broken in the troposphere / molecule reacts in the troposphere / reacts before reaching the stratosphere (1)

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Question 15 b

(b) Why did the scientists think their results from the ozone experiments were incorrect?

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Answer 15 b

so much data was being collected that any results outside the expected ranges were discarded (1),

the (concentration) values were significantly low for ozone (1) – this meant they were outside the range expected

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Question 16

16.     The equation below represents the reaction of hydroxyl radicals with carbon monoxide to produce carbon dioxide.

                                                                CO + OH → CO2 + H

Explain what is meant by the term radical. [1]

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Answer 16

A particle with one (or more) unpaired electron(s). (1)

Answer must be in the context of an electron as part of some sort of particle. ignore ‘free’ or ‘lone’ or single electron.

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Question 17

In the stratosphere, Br radicals act as catalysts to break down ozone.

(i)      Explain how the presence of ozone in the stratosphere benefits us. [3]

(ii)     Why is the action of bromine described as homogeneous catalysis? [1]

(iii)    In this question, one mark is available for the quality of spelling, punctuation and grammar.

          The breakdown of ozone in the stratosphere is speeded up by the presence of a catalyst.

          Give two other factors which will increase the rate of this reaction.

          Explain the increase in reaction rate in each case in terms of the reacting particles. [6]

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Answer 17

            (i)         it filters/screens/removes (AW) uv (1); plus two from:
(uv) of high energy/frequency/ UVC/UVB 1016 Hz/200-320nm (1);
which causes skin cancer/ harms skin/damages DNA (1);
affects crops (1) damages eyes (1);
damages immune system (1); growth of phytoplankton (1)

(ii)     reactants and catalyst in same phase/state       

(iii)    temperature (1) – molecules have more energy/ move faster (1);
more frequent collisions with energy greater than activation energy (1)
pressure/concentration (of ozone) (1) – more collisions (1) per unit time
intensity/amount of uv (1) greater amount of radiation breaks
more O3 per unit time/ more photodissociation/ more radicals (1)                 5

          QWC At least two sentences with spelling, punctuation and grammar

with only one error in all (1)                                                                               1 

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Question 18

It has been proposed that the substance ‘n-propyl bromide’, CH3CH2CH2Br, could be used as a suitable substitute for certain CFCs.

          One possible use of n-propyl bromide is as a substitute for the chlorofluorocarbon CFC-113.

          This CFC was used as a cleaning solvent for metals and electronic components.

Suggest two factors (apart from ozone depleting potential) that must be taken into account when considering n-propyl bromide as a replacement for CFC-113. [2]

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Answer 18

two from boiling point/volatility; flammability; toxicity/harm to health;
cost of manufacture (AW); (un)reactivity/stability/ease of disposal.
IGNORE greenhouse gases

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Question 19

If molecules of CH2F2 reach the stratosphere, they do not break down to produce F radicals.

Suggest why C–F bonds are not broken in the stratosphere. [2]

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Answer 19

uv/radiation (1);                                                                                                                     

          does not have high enough energy/ does not have high enough frequency (1)
REJECT for second mark answers which imply intensity of radiation

“C–F is strong/stronger than C–Cl” scores (1) only if no other mark awarded

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Question 20

Natural processes in the air can control the concentrations of some types of atmospheric pollutants. Although carbon monoxide emissions increased in the twentieth century, the percentage of carbon monoxide in the troposphere has remained almost constant.

The increased use of cars in the twentieth century is one reason for the increase in carbon monoxide emissions.

            (a) Explain the origin of these carbon monoxide emissions. [2]

 (b)    Give two reasons why carbon monoxide is classed as a polluting gas. [2]

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Answer 20

     (a)     Incomplete combustion (1) of hydrocarbons (1)

(b)     Toxic / poisonous / reduces the capacity of blood to carry oxygen around the body(1)


          Any one from:

          causes (photochemical) smog (1)

          oxidised to CO2 which is a greenhouse gas / reacts with O2 to form CO2 which is a greenhouse gas (1)


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Question 21

21.     One of the most important uses of platinum is as a catalyst.
Complete the enthalpy profile diagram below to show how a catalyst speeds up an exothermic reaction. The uncatalysed reaction takes place in a single step.

Show and label in your diagram the
              activation enthalpy without a catalyst
              activation enthalpy with a catalyst
              enthalpy change of reaction

[Total 5 marks]

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Answer 21

Enthalpy of products lower than reactants in both cases (1);                                                        
correct shape curve for reaction, single ‘hump’ (1);
correct shape curve for catalysed reaction, two ‘humps’ (1);
enthalpy change of reaction correct (1);
both enthalpy changes of activation correct (1).


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Question 22

In this question, one mark is available for the quality of the use and organisation of scientific terms.

          The cracking reaction in step 1 converts ethane into ethene and hydrogen. The reaction equation is shown below.

C2 H6(g)  C2H4(g) H2(g)    H = 138 kJ mol–1

          Altering the temperature and pressure conditions for the process given in the equation above can increase the rate of this reaction.

          Explain how the temperature and pressure could be changed in order to make the reaction faster. Use the ideas of activation enthalpy and collision theory to help you explain why your changes make the reaction faster. [7]

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Answer 22

          Increasing the temperature (makes the reaction faster) (1);
At higher temperatures the particles have more (kinetic)
energy/move faster/ vibration/ more frequent successful collisions (1);
More particles have an energy greater than the activation enthalpy
when they collide (1);
Increasing the pressure (makes the reaction faster) (1);
At higher pressures there are more particles per unit of volume/
closer together (1);
So more frequent collisions / more likely to collide/ collide more often/
greater chance of collision (1)                                                                           

          QWC: logical, correct use in context of at least three terms below:
molecule; particle; activation enthalpy/energy; kinetic/ vibrational
energy; collisions; rate (1)                                                                                   

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Question 23

Explain the term activation enthalpy [2]

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Answer 23

The minimum combined (kinetic) (1); energy on collision of particles                      
that will lead to a reaction (AW) (1) first mark depends on second

“breaking bonds in reactants” scores (1)

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Question 24

Carbon dioxide and silicon dioxide are both common in nature. Carbon and silicon are both in the same group of the Periodic Table and both form oxides of formula XO 2.

          Explain why silicon dioxide is a solid at room temperature while carbon dioxide is a gas. [3]

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Answer 24

SiO2 giant covalent/ network solid/ lattice/ whole structure held together by

covalent bonds (1) IGNORE “intermolecular”

CO2 molecular (AW) (1)

weak intermolecular forces (can be named and can be abbreviated

ALLOW permanent dipole - permanent dipole)/less energy needed to

separate molecules/ bonds in SiO2 are stronger (1)

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Question 25

The equation below represents the reaction that occurs when propene forms from propan-1-ol.

          CH3CH2CH2OH(g) CH3CH=CH2(g) + H2O(g)                ΔH = + 81 kJ mol−1

(a)     The reaction represented by the equation above can reach a position of dynamic equilibrium.
Explain what is meant by the term dynamic equilibrium. [2]

(b)     Describe and explain the effect of the following changes on the equilibrium amount of propene produced in the reaction represented by the equation above.

(i)      Increasing the total pressure of the reaction system. [2]

(ii)     Carrying out the reaction at a higher temperature. [2]

(c)     Describe and explain the effect of increasing the total pressure of the reaction system on the rate of production of propene  [3]

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Answer 25

(a)     rate of forward reaction = rate of back reaction (1)
concentrations of reactants and products remain constant / closed system (1)

(b)     (i)      describe mark –decrease in amount of propene (1) (increased pressure) pushes (position of) equilibrium to the side with fewest molecules (1) Must mention equilibrium for the second mark

(ii)     amount of propene produced increases (1) (increased temperature) pushes (position of) equilibrium in the endothermic direction / to the right / to the products (1) Must mention equilibrium for the second mark.

(c)     Any three from:

1.      increased pressure increases number of particles per
unit of volume (1) 
allow ‘particles are closer together’ for the first point do not allow ‘reactants are closer together’.

2.      more frequent collisions occur (1) More frequent collisions / collisions occur more oftenIgnore more likely to collide / greater chance of collisions in point 2.

3.      rate increases/gets faster (1)

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Question 26

26  (a)    Explain what is meant by the term photochemical dissociation. [2]

(b)     Describe and explain the way in which the temperature of the atmosphere changes on going from the surface of the Earth to the top of the stratosphere. [4]

(c)     Explain why reactions between atoms may occur more quickly at the top of the troposphere than in the middle of the stratosphere, even though the temperature at these points is the same. [2]

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Answer 26

(a)     splitting / breaking down a chemical / molecule / bond(1); using energy absorbed from UV / visible / light(1);

(b)     the temperature in the troposphere decreases as you move away from the Earth’s surface (1); because hot gases near the Earth’s surface rise & cool / higher concentrations of greenhouse gases / named gas lower down absorb more IR from Earth / the atmosphere is heated by the Earth low down(1); within the stratosphere the temperature of the atmosphere rises as you move away from the Earth (1); due to exothermic reactions (1);

(c)      the concentration of gases is higher in the troposphere / troposphere is more dense / pressure is higher ORA (1); so there are more collisions per second / more frequent collisions (in the troposphere) (1);do not allow ‘more collisions’ or ‘more chance of collisions’

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Question 27

Chloroethene will undergo the following sequence of reactions.

chloroethene       chloroethane         ethanol                  ethanal

(i)      Name the reagent and conditions needed to turn chloroethene into chloroethane.[2]

(ii)     Classify ethanol as primary, secondary or tertiary, giving a reason. [2]

 (iv)   Give the reagents and conditions for the conversion of ethanol to ethanal in the laboratory. [3]

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Answer 27

Hydrogen (1);

            Ni, hot or Pt (room temperature and pressure) (1)

(ii)        Primary (1);
as OH is attached to CH2/ C with OH attached to one other C (1)

(iv)       (potassium/sodium) dichromate/ correct formula (1);
(sulfuric) acid (1);
distil (1) NOT heat

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Question 28

The equation below represents the reaction that occurs when propene forms from propan-1-ol.

          CH3CH2CH2OH(g) CH3CH=CH2(g) + H2O(g)                ΔH = + 81 kJ mol−1

          Give the reagents and conditions required for the reaction represented by the equation. [3]

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Answer 28



sulfuric / phosphoric acid (1)

heat / reflux (1)

concentrated (1)



alumina / silica/ pumice /
porous pot (1)

heat (1)

with (propan-1-ol) vapour (1)

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Question 29

The student carried out the reaction of propene with hydrogen at room temperature and pressure by carefully choosing the catalyst to use. Name the catalyst that would be required under these reaction conditions. [1]

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Answer 29

platinum (1)

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Question 30

Chloroethene will undergo the following sequence of reactions.

chloroethene      chloroethane           ethanol           compound A

          Much of the ethanol is made industrially from ethene.

Give the reagents and conditions by which ethanol is made from ethene in industry. [2]

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Answer 30

Water (1);

            Catalyst with high temp & pressure/ catalyst of sulfuric or phosphoric acid (1)
(second mark dependant on first)

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Question 31

Chlorine is used to convert ethene into 1,2-dichloroethane in an electrophilic addition reaction. Explain what is meant by the terms electrophilic and addition. [3]

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Answer 31

(Partially) positively charged/electron deficient reagent/attracted to areas of high electron density (1);

Bonds by accepting a pair of electrons (can be shown via mechanism) (1);

Two molecules react to form one product  (1)

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Question 31

What is meant by cis-trans isomerism? [1]

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Answer 31

Different arrangement (of groups) around a (carbon–carbon)
double bond (1)
Allow from diagram (1) ALLOW other centres of restricted rotation

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Question 32

The alcohol group in the side-chain can be oxidised to a carboxylic acid.

Give the reactants and conditions needed to carry out this oxidation reaction in a laboratory. [3]

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Answer 32

(potassium) dichromate (1);
(sulphuric) acid (1);
reflux/ heat (if first mark scored) (1)

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Question 33 b

Bromine reacts with an alkene to form a dibromoalkane.

(b)     Bromine also reacts with alkanes.

What conditions are necessary for this reaction to occur? [1]

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Answer 33 b

(b)     light (on its own or qualified “visible”, “uv” “sun”, “radiation”)/u.v. (radiation)

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Question 34

One way to analyse the air bubbles from Antarctic ice is to use infrared spectroscopy. This process involves passing infrared radiation of known frequencies through the gas mixture and measuring the amount of radiation that is absorbed at each frequency value.

(i)      The air must be dried before it can be put into the infrared spectrometer. Name a drying agent that could be used. [1]

(ii)     Explain why molecules absorb infrared radiation of specific frequencies. [2]

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Answer 34

(i)      (anhydrous) sodium sulphate or other suitable salt/silica gel (1)                               

ALLOW conc. H2SO4

(ii)     The bonds need a specific frequency to make them (1); vibrate                      
(more) (1); second mark if bond or molecule mentioned

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Question 35

In this question, one mark is available for the quality of spelling, punctuation and grammar.

          When the chemists measured the concentration of NO in the stratosphere, they realised that there was not enough NO to cause significant ozone depletion at that time.

          Concentrations of NO can be measured by infrared spectroscopy.

          What effect does infrared radiation have on NO molecules?
Suggest how infrared spectroscopy could be used to show

•   the presence of NO

•   the concentration of NO in a sample of the atmosphere. [6]

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Answer 35

1 mark for point in bold and any 4 other points from 5:
Infrared radiation is absorbed by NO / NO molecule excited by / NO is given energy (1);
NO bond / molecule (1);

          vibrates (1)
more / may answer in terms of higher vibrational energy levels (1);
at a specific frequency / wavelength / allow in terms of  ‘characteristic
absorption’ (1);
more IR absorbed by higher concentrations of NO / larger peak in IR
spectrum / relationship mark between absorbance and concentration (1).

At least two readable and clear sentences with no more than one spelling,
punctuation or grammatical error (1).


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Question 36

Explain why trans poly(isopropene) cannot be rotated to give cis poly(isopropene). [1]

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Answer 36

The C=C double bond can’t be rotated (1)

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Question 37

Explain the meaning of the term thermoplastic. [1]

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Answer 37

Softens/ flows/ melts when heated/ warmed (1)

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Question 38

(a) Suggest how ultraviolet light might affect rubber. [3]

(b)     Explain how vulcanisation improves the properties of rubber and accelerator molecules catalyse the process. [6]

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Answer 38

(enough) energy (1);
to break bonds (1);
breaking down structure (1)

(b)        strong S–S bonds (1);
stop chains sliding over each other (1)
 relation between strong bonds and stopping sliding (1)
path of lower Ea (1);
molecules contain sulfur (1);
form intermediates (1)

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Question 39

How would you test a sample for unsaturation. [3]

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Answer 39

Add bromine water (1);
Bromine water is decolourised/ colour changes from brown (1)
to colourless if sample contains unsaturated bonds (1)  

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Question 40

Large quantities of chloromethane, CH3Cl, and bromomethane, CH3Br, are released into the Earth’s troposphere (lower atmosphere) each year from marine life in the oceans.

Chloromethane and bromomethane are both gases at room temperature whilst water is a liquid.

(i)      Water molecules are held together by hydrogen bonds. Draw a diagram to show how two water molecules can be linked by a hydrogen bond. Include relevant lone pairs and partial charges in your diagram. [4]

(ii)     Describe two features of a water molecule that enable it to form hydrogen bonds. [2]

(iii)    Propan-1-ol has a higher boiling point than propene. Explain this in terms of intermolecular bonding. [4]

*   In your answer, you should make it clear how the steps you describe are linked to one another.

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Answer 40

 can be shown on either O)
Water molecule shape drawn correctly (1);
(lose this mark if HO2 but can score others. 
 Lone pair on relevant O pointing along bond (1); Partial charges shown, one O (shown δ) and one H (shown δ+) (1); O–H–O straight (1)

(ii)     Non-bonding/lone/unshared pair on oxygen / oxygen atom small* & electronegative (  hydrogen with δ+ charge / H in polarised O–H bond (*or very/high electronegativity)

1.      intermolecular bond in propene is instantaneous dipole-induced
dipole (1)

2.      hydrogen bonds / intermolecular bonds (in propan-1-ol) are
stronger than those in propene (ORA) (1) 
do not allow harder / easier

3.      intermolecular bonds must be broken for the liquid to boil (1)

4.      more energy is needed to break them (ORA) (1) do not allow ‘higher temperature’ for ‘more energy’.


          QWC – mark for connection of ideas: idea of linking strength of
intermolecular bonds to amount of energy needed to break them (1)

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Question 41

The reaction represented by equation CO + OH → CO2 + H produces carbon dioxide, which is a gas at room temperature. Silicon dioxide, another Group 4 oxide, is a solid at room temperature.

          Explain this difference in terms of bonding and structure.

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Answer 41

          SiO2: giant covalent / network solid / lattice / whole structure held together
by covalent bonds / diagram (1)

ignore ‘intermolecular bonds’ in SiO2 / giant molecule /
can be given for a labelled / annotated diagram

          CO2: simple molecular / molecules / O=C=O / AW (1)

ignore ‘covalent’.

          comparison of forces: weak intermolecular bonds (or forces) in CO2 / less
energy needed to separate molecules / bonds in SiO2 are stronger than CO2
intermolecular bonds (or forces) (1)

Any type of intermolecular bonds can be named and can be abbreviated.
must be clear that the intermolecular bonds in CO2 are being discussed, not the covalent bonds.



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