2016-

Question 1

Suggest one reason, other than incomplete combustion or heat transfer to the atmosphere, why the student’s value for the enthalpy of combustion of methanols different from that in a Data Book.

Answer 1

Experiment not done under standard conditions

Question 2

The student said correctly that using a thermometer with an overall uncertainty for
the rise in temperature of ±0.5 °C was adequate for this experiment.
Explain why this thermometer was adequate for this experiment.

Answer 2

Idea that temperature change/rise is (significantly / much)

bigger than uncertainty/Idea that heat loss is more significant issue

Question 3

Identify a reagent that could be used in a chemical test to show that oleic acid is unsaturated.
State what would be observed in this test.

Answer 3

bromine water 
(orange/yellow to) colourless

Question 4

Explain why determining the precise relative molecular mass of propanal and prop-2-en-1-ol by mass spectrometry could not be used to distinguish between samples of these two compounds.

Answer 4

have the same molecular formula

so have the same relative molecular mass

Question 5

Predict the relative boiling points of these three compounds from the highest to the lowest boiling points.
Justify this order in terms of intermolecular forces.

Answer 5

Correct order (highest to lowest) =
prop-2-en-1-ol > propanal > butane
 Prop-2-en-1-ol has hydrogen bonds
 Propanal has (permanent) dipole-dipole forces
 Butane has van der Waals’ forces
 Strength of intermolecular forces:
hydrogen bonds > dipole-dipole > van der Waals

Question 6

Draw a labelled diagram to show how you would set up apparatus for refluxing.

Answer 6

flask with condenser vertically above it (without gaps
between flask and condenser)
flask and condenser labelled

Question 7

Anti-bumping granules are placed in the flask when refluxing.
Suggest why these granules prevent bumping.

Answer 7

form small(er) bubbles or prevent large bubbles

Question 8

Deduce which of Na+ and Mg2+ is the smaller ion.

Explain your answer.

Answer 8

Mg(2+) or Magnesium

Because Mg2+ has more protons

Question 9

Write an equation to represent the process that occurs when the first ionisation energy for sodium is measured.

Answer 9

Na(g) → Na+(g) + e−

Question 10

Explain why the first ionisation energy of sulfur is different from that of phosphorus.

Answer 10

e− paired in (3)p orbital in S

Paired e− repel (so less energy needed to remove)

Question 11

Name the type of bond formed between N and Al in H3NAlCl3 and explain how this bond is formed.

Answer 11

Dative (covalent) /co-ordinate bond

Shared pair of / both electrons come from the N(H3)

Question 12

Explain how the value of the Cl-Al-Cl bond angle in AlCl3 changes, if at all, on formation of the compound H3NAlCl3

Answer 12

Aluminium is now surrounded by 4 electron pairs/bonds or is tetrahedral
Therefore Cl-Al-Cl bond angle decreases / changes (from 120° in AlCl3 ) to allow range 107-111° in H3NAlCl3

Question 13

A solution of sodium chlorate(l) was added to a colourless solution of potassium iodide.
Suggest what is observed.
Explain the reaction that leads to this observation.

Answer 13

Goes brown (or shades of brown)
Due to iodine or I^3−
Because I− oxidised

Question 14

Write an ionic equation, with state symbols, to show the reaction of calcium with an excess of water.

Answer 14

Metal(s) + H20(l) –> MetalOH(aq) + H2(g)

Question 15

State the role of water in the reaction with calcium.

Answer 15

Oxidising agent

Question 16

Write an equation to show the process that occurs when the first ionisation energy of calcium is measured.

Answer 16

Ca(g) Ca+(g) + e–

Question 17

State and explain the trend in the first ionisation energies of the elements in Group 2 from magnesium to barium.

Answer 17

Decrease
Ions get bigger / more (energy) shells
Weaker attraction of ion to lost electron

Question 18

Describe how ions are formed in a time of flight (TOF) mass spectrometer.

Answer 18

the sample is bombarded by high energy electrons

the sample molecule loses an electron forming M+

Question 19

Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer.

Answer 19

Ions, not molecules, will interact with and be accelerated by an electric field
Only ions will create a current when hitting the detector

Question 20

Explain why CF4 has a bond angle of 109.5°.

Answer 20

Around carbon there are 4 bonding pairs of electrons (and no lone pairs)
Therefore, these repel equally and spread as far apart as possible

Question 21

The student added a few drops of Y(aq) to the equilibrium mixture of X(aq), Y(aq) and Z(aq) in Question 4.3.
Suggest how the colour of the mixture changed. Give a reason for your answer.

Answer 21

Darkened / went more orange
The equilibrium moved to the right
To oppose the increased concentration of Y

Question 22

The student warmed the equilibrium mixture from Question 4.3.
Predict the colour change, if any, when the equilibrium mixture was warmed.

Answer 22

The orange colour would fade

Question 23

Sodium bromide reacts with concentrated sulfuric acid in a different way from sodium chloride.
Write an equation for this reaction of sodium bromide and explain why bromide ions react differently from chloride ions.

Answer 23

2NaBr + 2H2SO4 Na2SO4 + Br2 + SO2 + 2H2O

Br– ions are bigger than Cl– ions
Therefore Br– ions more easily oxidised / lose an electron more easily (than Cl– ions)

Question 24

A colourless solution contains a mixture of sodium chloride and sodium bromide.
Using aqueous silver nitrate and any other reagents of your choice, develop a procedure to prepare a pure sample of silver bromide from this mixture.
Explain each step in the procedure and illustrate your explanations with equations, where appropriate.

Answer 24

Stage 1: formation of precipitates
• Add silver nitrate
• to form precipitates of AgCl and AgBr
• AgNO3 + NaCl → AgCl + NaNO3
• AgNO3 + NaBr → AgBr + NaNO3

Stage 2: selective dissolving of AgCl
• Add excess of dilute ammonia to the mixture of
precipitates
• the silver chloride precipitate dissolves
• AgCl + 2NH3 → Ag(NH3)2+ + Cl–

Stage 3: separation and purification of AgBr
• Filter off the remaining silver bromide precipitate
• Wash to remove soluble compounds
• Dry to remove water

Question 25

The mass of MgO obtained in this experiment is slightly less than that expected from the mass of Mg(NO3)2 used.
Suggest one practical reason for this.

Answer 25

Some of the solid is lost in weighing product

Question 26

Explain how the Cahn-Ingold-Prelog (CIP) priority rules can be used to deduce the full IUPAC name of this compound.

Answer 26

Stage 1: consider the groups joined to right hand carbon of the C=C bond
Consider the atomic number of the atoms attached
C has a higher atomic number than H, so CH2OH takes priority

Stage 2: consider the groups joined to LH carbon of the C=C bond
Both groups contain C atoms, so consider atoms one bond further
away C, (H and H) from ethyl group has higher atomic number than H, (H
and H) from methyl group, so ethyl takes priority

Stage 3: conclusion
The highest priority groups, ethyl and CH2OH are on same side of
the C=C bond so the isomer is Z
The rest of the IUPAC name is 3-methylpent-2-en-1-ol

Question 27

State how your answer to Question 2.2 is likely to differ from the value quoted in
reference sources.
Give one reason for your answer.

Answer 27

Less negative than the reference

Heat loss

Question 28

A 50.0 g sample of water was used in this experiment.

Explain how you could measure out this mass of water without using a balance.

Answer 28

Water has a known density (of 1.0 g cm–3)

Therefore, a volume of 50.0 cm3 could be measured out

Question 29

State the meaning of the term structural isomers.

Answer 29

(Compounds with the) same molecular formula but different structural formula

Question 30

Write an equation for the reaction occurring during fermentation.

Answer 30

C6H12O6 –> 2C2H5OH + 2CO2

Question 31

In industry, this fermentation reaction is carried out at 35 °C rather than 25 °C.
Suggest one advantage and one disadvantage for industry of carrying out the fermentation at this higher temperature.

Answer 31

Adv: ethanol is produced at a faster rate
Dis: more energy is used / required in the reaction

Question 32

The method used by the student in Question 4.2 would result in the ethanol being contaminated by ethanoic acid.
How does this contamination occur?

Answer 32

Air gets in / oxidation occurs

Question 33

Give two differences between the infrared spectrum of a carboxylic acid and that of an alcohol other than in their fingerprint regions.

Answer 33

Alcohol OH absorption in different place (3230–3550 cm–1) from acid OH
absorption (2500–3000 cm–1)
The C=O in acids has an absorption at 1680–1750 cm–1

Question 34

Reaction 1 is an example of thermal cracking and is carried out at a temperature
of 750 °C.
State one other reaction condition needed.

Answer 34

High Pressure

Question 35

Reaction 2 is exothermic. A typical compromise temperature of 200 °C is used industrially for this reaction.
Explain the effect of a change of temperature on both the position of equilibrium and the rate of reaction, and justify why a compromise temperature is used industrially

Answer 35

Stage 1: consider effect of higher temperature on
yield
• Le Chatelier’s principle predicts that equilibrium
shifts to oppose any increase in temperature
• Exothermic reaction, so equilibrium shifts in
endothermic direction / to the left
• So a Higher T will reduce yield

Stage 2: consider effect of higher temperature on rate
• At higher Temperature, more high energy
molecules
• more collisions have E>Ea
• So rate of reaction increases/time to reach
equilibrium decreases

Stage 3: conclusion
Industrial conditions chosen to achieve (cost-effective)
balance of suitable yield at reasonable rate

Question 36

In a trial experiment, the student failed to fill the burette correctly so that the gap between the tap and the tip of the burette still contained air.
Suggest what effect this would have on the measured volume of bromine water in this
trial. Explain your answer.

Answer 36

Measured volume would be greater

Level in burette falls as tap is filled before any liquid is delivered

Question 37

Other than incorrect use of the burette, suggest a reason for the inconsistency in the student’s results.

Answer 37

Drop sizes vary

Question 38

Outline how the student could improve this practical procedure to determine the number of C=C double bonds in a molecule of the oil so that more consistent results are obtained.

Answer 38

Use a larger single volume of oil
Dissolve this oil in the organic solvent
Transfer to a conical flask and make up to 250 cm3 with more solvent Titrate (25 cm3) samples from the flask