2016 ppq

Question 1

The [Fe(H2O)6]2+ ion has unpaired electrons and is therefore
paramagnetic.
Explain how unpaired electrons can arise in this complex ion. (splittings go over it)

Answer 1

1 mark is awarded for recognising that there is a small energy gap.
1 mark is awarded for recognising that electrons are promoted.

Question 2

Explain why all of the complex ions formed by the Fe3+ ion are paramagnetic

Answer 2

It has a half-filled d-subshell

Question 3

Suggest an analytical technique that could be used to determine
the presence of copper ions in spiders’ blood.

Answer 3

Flame test

Question 4

state what is meant by “weigh accurately approximately” 4∙25 g of solid silver nitrate.

Answer 4

The exact mass should be known/measured and should be close to 4∙25 g

Question 5

Outline how the student would have prepared the standard silver nitrate solution.

Answer 5

Dissolve a solution of the silver nitrate in deionised water (in a beaker).
Transfer the solution and the rinsings (to the standard flask) (1)
Make (the solution) up to the mark in a standard flask (with deionised water).

Question 6

Samples of the diluted seawater were titrated and the average titre was found to be 3∙9 cm3.
Suggest an improvement the student could make to reduce the uncertainty in the titre value. 1

Answer 6

Dilute the standard silver nitrate solution

Question 7

For the gravimetric method, standard silver nitrate solution was added to a seawater sample to form a precipitate of silver chloride.
(i) Describe how the filtration should have been carried out to ensure
a fast means of separating the precipitate from the reaction mixture. 1

Answer 7

Vacuum filtration

Question 8

After the precipitate was filtered, the filtrate was tested with a few drops of silver nitrate solution.
Suggest why the student tested the filtrate in this way.

Answer 8

To check the reaction is complete

Question 9

The student also planned to carry out an analysis of chloride ion concentration in fresh river water.
Explain why the volumetric method, rather than the gravimetric method, would be more appropriate for the analysis of chloride ion concentration in fresh river water.

Answer 9

Gravimetric method would produce too little/no precipitate.

Question 10

Suggest why the optical activity of 3-methylpentan-2-one decreases over time.

Answer 10

A racemic mixture is forming

Question 11

State what is meant by the term agonist.

Answer 11

An agonist is a molecule which behaves like/mimics/enhances/triggers the natural response (of the body)

Question 12

Suggest a suitable reagent that could be used to convert the ketone carbonyl group to the hydroxyl group.

Answer 12

LiAlH4 or lithium aluminium hydride

Question 13

State the type of hybridisation which is adopted by the carbon atoms in the aromatic ring.

Answer 13

sp2

Question 14

Describe how pi bonds form.

Answer 14

Orbitals overlap sideways

Question 15

Complete the diagram below to show how the reaction mixture is heated under reflux.
Do in own time now

Answer 15

.

Question 16

At the start of the reaction, two layers were observed in the reaction mixture.
Explain why only one layer was observed when the reaction was complete.

Answer 16

The (named) product/products are soluble/ miscible/have dissolved

Question 17

Explain fully why a solution of the salt sodium 4-hydroxybenzoate
has a pH greater than 7.

Answer 17

The (4-hydroxybenzoate) ion from the salt removes/ reacts with H+ from the water
OR
Conjugate base of a weak acid, removes/reacts with H+ from the water (1)
This results in the water equilibrium shifting to the right hand side
OR
shifting to the left hand side if candidate has written an equilibrium reaction with ions on the left hand side
OR
This results in the water equilibrium producing an excess of OH- ions.

Question 18

State two factors that should be considered when selecting an appropriate solvent for this recrystallisation.

Answer 18

being more soluble in the hot solvent than in the cold
boiling point
polarity.