LOK Questions

Question 1

Give two reasosn why different amino acids have different Rf values. (2)

Answer 1

• amino acids have different solubility / adsorption
  to the stationary phase (1)
• amino acids have different solubility in the mobile
  phase (1)

Question 2

State why argon and nitrogen are suitable carrier gases for gas chromatography. (1)

Answer 2

gases are inert / do not react
(with the components of the mixture)

Question 3

State how anti-bumping granules prevent bumping (1)

Answer 3

An answer that makes reference to the following
prevention of uncontrolled boiling by:
- distributing the heat more evenly
or
- providing a surface for bubbles to form/allow
smaller bubbles to form/provides nucleation sites
for bubbles

Question 4

Using the apparatus for distillation instead of reflux is not an efficient way to produce ethanoic acid from ethanol. Explain why. (2)

Answer 4

An explanation that makes reference to the following
- ethanol would be oxidised to ethanal (1)
- because ethanal has a low boiling temperature
or
ethanal will distil before ethanoic acid can be
formed

Question 5

Devise an experiment, giving outline to details only, that would enable the relative rates of hydrolysis of halogenoalkanes to be compared. (5)

Answer 5

An answer that gives reference to the following
 (M1) use of ethanol (as a solvent) (1)
 (M2) use of silver nitrate (solution) (1)
 (M3) equal amounts used of each halogenoalkane (1)

 (M4) measure the time taken for precipitate to form (1)
 (M5) use a water bath (to control a raised temperature)
(1)

Question 6

Explain the trend in rates of hydrolysis of 1-chlorobutane, 1-bromobutane and 1-iodobutane. (2)

Answer 6

An explanation that makes reference to the following
 the reaction rate is in the order
1-chlorobutane<1-bromobutane<1-iodobutane
(1)
 because the C-Cl bond is stronger than the C-Br
bond which is stronger than the C-I bond (1)

Question 7

Manganate (VII) ions react with ethanedioate ions in acid solution. The reaction starts slowly, the rate of reaction then increases, before it decreases again. Explain this sequence.

Answer 7

Initially, both reactants are negatively charged which causes them to repelt therefore causing the slow rate of reaction.
The rate then increases due to the formation of Mn2+ ions which act as a catalyst.
The rate then decreases again due to the decrease in concentration of the reactants.

Question 8

What cheimcal is contained in the salt bridge?

Answer 8

KNO₃

Question 9

Give a possible reason why the salt bridge cannot be replaced by an unreactive wire.

Answer 9

Purpose of the salt bridge is to allow the flow of positive ions. Wire only allows the flow of electrons.

Question 10

You’re given two substances with both their theoretical and experiment lattice energies. You’ve been asked to comment on the values and explain any differences and simalarities. What should you compare/mention in your answer.

Answer 10

Describe bonding in both substances (whether 100% ionic or contains covalent character)
Compare the charge on the cations
Compare the polarizing ability of the cations
Compare the size of the anions
Compare ability of anion to be polarised