P4: Practical

Question 1

2: (Thermochemistry)
- if ^T is too small,

• if ^T is too large,

Answer 1

• percentage error of temperature measurement is too large
• more heat is lost to the surrounding which is not fully compensated because of differential rate or heat lost

Question 2

3: (Kinetics)
why deioniser water is added to ensure that the same total volume of reaction mixtures is used in all experiments

Answer 2

• To ensure that the concentration of mixture is directly proportional to the volume of reactant added
• So that the depth of the reaction mixture is constant, to ensure that the same amount of sulfur is formed in each experiment -> rate directly proportional to relative rate

Question 3

3:
safety hazard and precaution of using SO2 gas

Answer 3

• SO2 gas is toxic/ irritates eyes and respiratory tract
• The experiment should be carried out in a fume cupboard

Question 4

3: (Kinetics)
Explain the role of starch indicator and how it affects the reliability of the results

Answer 4

• The starch indicator forms a dark blue colour with iodine, which makes the colour change from colourless to dark blue more distinct
• It is easier to determine the time taken for the appearance of iodine, thus increasing the reliability of the results

Question 5

3:
safety hazard and precaution of using iodine

Answer 5

• Iodine vapour is toxic and can irritate the respiratory system
• The reaction mixtures should be discarded immediately/ conduct the experiment in a fume cupboard

Question 6

3: (kinetics)
why the rate of reaction between peroxydisulfate ions and iodide ions takes place relatively slowly

Answer 6

• Since peroxydisulfate and iodide and both negatively charged, they will repel each other. thus the reaction has a high activation energy.
• less particles possesses energy greater than or equal to high activation energy, hence frequency of effective collisions is low. According to the collision theory, rate of reaction is slow

Question 7

3: (kinetics)
why deionised water is added to the 25.0cm^3 aliquot

Answer 7

A large volume of water is added to reduce the concentration of the reactants significantly, hence quenching the reactant