Specimen

Question 1

Explain how the electron pair repulsion theory can be used to deduce the shape of,
and the bond angle in, PF3

Answer 1

Stage 1: Electrons round P
• P has 5 electrons in the outside shell
• With 3 electrons from 3 fluorine, there are a total
of 8 electrons in outside shell
• so 3 bond pairs, 1 non-bond pair
Stage 2: Electron pair repulsion theory
• Electron pairs repel as far as possible
• Lone pair repels more than bonding pairs
Stage 3: Conclusions
• Therefore, tetrahedral / trigonal pyramidal shape
• With angle of 109(.5)° decreased to 107°

Question 2

Explain why sodium oxide forms an alkaline solution when it reacts with water

Answer 2

Sodium oxide contains O2– ions

These O2– ions react with water forming OH– ions

Question 3

Suggest one reason why electron pair repulsion theory cannot be used to predict the
shape of the [CoCl4]
2– ion.

Answer 3

Too many electrons in orbitals

Question 4

Another structural isomer of J is shown below.
CH3CH2C=CCH3CH2OHH
Explain how the Cahn-Ingold-Prelog (CIP) priority rules can be used to deduce the full
IUPAC name of this compound. (6 marks)

Answer 4

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 5

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.
[6 marks]

Answer 5

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 6

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.
[4 marks]

Answer 6

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 samples from the flask