Experiment 1.2 – Effect of concentration on the rate of reaction.
Aim: To investigate the effect of concentration of a reactant on the rate of reaction.
Problem statement:
Hypothesis:
How does the concentration of a reactant affect the rate of
reactant?
When the concentration increases, the rate of reaction becomes
higher.
Variables:
Manipulated variable:
Responding variable:
Controlled variable:
Concentration of sodium thiosulphate solution
Rate of reaction
Temperature, total volume of the reacting
mixture, concentrated and volume of sulphuric
acid, size of conical flask
Apparatus: 150 cm3 conical flasks, 50 cm3 measuring cylinder, 10 cm3 measuring
cylinder, stopwatch.
Materials: 0.2 mol dm-3 sodium thiosulphate solution, 1.0 mol dm-3 sulphuric acid,
distilled water, white paper with a mark ‘X’ at the centre.
DIAGRAM (Figure 1.7 pg
11 practical book)
Procedure:
1. By using a measuring cylinder, 45 cm3 of 0.2 mol dm-3 sodium
thiosulphate solution was poured into a conical flask.
2. The conical flask was placed on top of a piece of white paper with a
mark ‘X’.
3. By using another measuring cylinder, 5 cm3 of 1.0 mol dm-3 sulphuric
acid was poured quickly and carefully into the conical flask and the
stopwatch was started immediately.
4. The mixture in the conical flask was swirled a few times and placed it
back on the white paper.
5. The mark ‘X’ was observed vertically from the top through the solution
as shown in the diagram above.
6. The time t required for the mark ‘X’ to disappear from sight was
recorded.
7. The experiment was repeated four more times using different volumes
of 0.2 mol dm-3 sodium thiosulphate solution to be diluted with different
volumes of distilled water as shown in the table below. The other
conditions remain unchanged.
8. The results were recorded.
Data and Observation:
Set
I
II
III
IV
V
Volume of
Volume
Concentration
Total
-3
0.2 mol dm
Volume
of 1.0
of sodium
volume
sodium
of
mol dm-3
thiosulphate
1/time,
of
Time
thiosulphate, distilled sulphuric
solution, M2
1/t (sreacting
(s)
-3
1)
Na2S2O3
water
acid,
(mol dm )
mixture,
3
solution, V1
(cm )
H2SO4
M2 = M1V1
V2 (cm3)
3
3
(cm )
(cm )
V2
45.0
0.0
5.0
50.0
0.18
18.18
40.0
5.0
5.0
50.0
0.16
20.05
30.0
15.0
5.0
50.0
0.12
26.98
20.0
25.0
5.0
50.0
0.08
40.82
10.0
35.0
5.0
50.0
0.04
83.24
Interpreting Data:
4.
Based on graph concentration of sodium thiosulphate solution against time, as
the concentration of sodium thiosulphate solution decreases, a longer time is
needed for mark ‘X’ to disappear from sight. Therefore, as the concentration
becomes lower, the rate of reaction also decreases.
Based on graph concentration of sodium thiosulphate solution against 1/time, it
implies that the concentration of sodium thiosulphate solution is directly
proportional to 1/time.
5.
Based on the deduction in (4), the relationship between the rate of reaction and
the concentration of sodium thiosulphate solution is, when the concentration of a
reactant increases, the rate of reaction increases.
Disscussion:
1. Necessary precautions to be taken in this experiments are:
a. Be careful when handling acid because it is corrosive.
b. The stopwatch must be started immediately when acid was poured into
the conical flask.
c. The conical flask must be swirled to ensure that the reactant mixes well.
2. The ionic equation for the reaction between sodium thiosulphate solution and
sulphuric acid is:
S2O32-(aq) + 2H+(aq) → S(s) + SO2(g) + H2O(l)
3. Different volumes of distilled water are added to the 0.2 mol dm
Conclusion:
When the concentration of sodium thiosulphate increases, the rate of
reaction increases. Hypothesis is accepted.