Section A
Answer all questions in this section.
o A value for enthalpy of solution can be determined from the results of
a calorimetry experiment or by the application of Hess's law.
n
I
Give the equation, including state symbols, for the process that
occurs when the enthalpy of solution of potassium hydroxide is
determined.
(1 mark
,0 1 .A student does an experiment to determine a value for the enthalpy of
2 solution of potassgurn hydroxide.
The student uses this method.
• Add some distilled water to a measuring cylinder and record
the volume.
• pour the water into a polystyrene cup.
• Record the temperature of the water in the cup.
• Add 3.00 g of solid KOH to the water in the cup.
• Stir the solution and record the maximum temperature
reached.
Table 1 shows the student's results.
Table 1
Initial
18.1
temperature / oc
Final temperature /
30.4
o
c
The student calculated the enthalpy of solution of
potassium hydroxide to be —51.3 kJ mol-I
The specific heat capacity of the solution, c = 4.18 J K-1 g-'
Assume the density of the solution = 1.00 g cm-3
Calculate the volume of water that the student added to the cup.
[5 marks]
, Volume of water Units
Table
Use
3
, Enthalpy of solution kJ mop
Suggest why the value calculated in Question 01.3 is different
from the experimental value given in Question 01.2.
(1 mar
The effect of reactant concentrations on the rate of a reaction is investigated.
The equation for the reaction is shown.
H202(aq) + 21-(aq) + 2H'(aq)12(aq) + 2H20(l)
The experiment is done five times in the presence of thiosulfate ions
and starch. The reactant concentrations are varied by changing the
volume of each reactant in the mixture.
The thiosulfate ions react with the iodine as it is produced, until
all the thiosulfate has reacted.
12(aq) + 2S2032-(aq) 21-(aq) + S4062-(aq)
After all the thiosulfate has reacted, the iodine produced in the
mixture then reacts with the starch and the solution turns blue-black.
The time taken for the solution to turn blue-black is recorded.
If the amount of thiosulfate is the same in each experiment, the time
recorded represents the time to produce the same amount of iodine
in each experiment.
Table 3 shows the results of the investigation.
Table 3
[1-1 Time for reaction
Experime [H2021
I mol dm- 1 mol mixture to turn
nt I mol dm-3
3 dm-3 blue-black I s
1 0.010 0.010 0.10 60
2 0.020 0.010 0.10 30
3 0.030 0.010 0.10 20
4 0.030 0.020 0.10 10
5 0.030 0.020 0.20 10
Answer all questions in this section.
o A value for enthalpy of solution can be determined from the results of
a calorimetry experiment or by the application of Hess's law.
n
I
Give the equation, including state symbols, for the process that
occurs when the enthalpy of solution of potassium hydroxide is
determined.
(1 mark
,0 1 .A student does an experiment to determine a value for the enthalpy of
2 solution of potassgurn hydroxide.
The student uses this method.
• Add some distilled water to a measuring cylinder and record
the volume.
• pour the water into a polystyrene cup.
• Record the temperature of the water in the cup.
• Add 3.00 g of solid KOH to the water in the cup.
• Stir the solution and record the maximum temperature
reached.
Table 1 shows the student's results.
Table 1
Initial
18.1
temperature / oc
Final temperature /
30.4
o
c
The student calculated the enthalpy of solution of
potassium hydroxide to be —51.3 kJ mol-I
The specific heat capacity of the solution, c = 4.18 J K-1 g-'
Assume the density of the solution = 1.00 g cm-3
Calculate the volume of water that the student added to the cup.
[5 marks]
, Volume of water Units
Table
Use
3
, Enthalpy of solution kJ mop
Suggest why the value calculated in Question 01.3 is different
from the experimental value given in Question 01.2.
(1 mar
The effect of reactant concentrations on the rate of a reaction is investigated.
The equation for the reaction is shown.
H202(aq) + 21-(aq) + 2H'(aq)12(aq) + 2H20(l)
The experiment is done five times in the presence of thiosulfate ions
and starch. The reactant concentrations are varied by changing the
volume of each reactant in the mixture.
The thiosulfate ions react with the iodine as it is produced, until
all the thiosulfate has reacted.
12(aq) + 2S2032-(aq) 21-(aq) + S4062-(aq)
After all the thiosulfate has reacted, the iodine produced in the
mixture then reacts with the starch and the solution turns blue-black.
The time taken for the solution to turn blue-black is recorded.
If the amount of thiosulfate is the same in each experiment, the time
recorded represents the time to produce the same amount of iodine
in each experiment.
Table 3 shows the results of the investigation.
Table 3
[1-1 Time for reaction
Experime [H2021
I mol dm- 1 mol mixture to turn
nt I mol dm-3
3 dm-3 blue-black I s
1 0.010 0.010 0.10 60
2 0.020 0.010 0.10 30
3 0.030 0.010 0.10 20
4 0.030 0.020 0.10 10
5 0.030 0.020 0.20 10
