An investigation into what affects the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid
Daniel John Constable (8041)
An investigation into what affects the rate of reaction between Sodium
Thiosulphate and Hydrochloric Acid
Investigation to find out how the rate of reaction between sodium
thiosulphate and hydrochloric acid is affected by changing the
concentration.
Introduction
In this experiment I am going to find out how the rate of reaction
between sodium thiosulphate and hydrochloric acid is affected by
changing the concentration.
We place the reaction mixture on a paper with a black cross-drawn on
it. When the cross is completely hidden, the reaction will have
finished. The time taken for this to happen is the measure of the rate
of reaction. We must do this several times, and change the
concentration of sodium thiosulphate, in order for us to determine if
it is a safe test.
The rate of reaction is a measure of the `change', which
happens during a reaction in a single unit of time. The things that
affect the rate of reaction are as follows:
· Surface area of the reactants
· Concentration of the reactants
· The temperature at which the reaction is carried out
· Light
· Use of a catalyst
The factor which we are using is Concentration of the reactants.
Plan
Apparatus
· Conical flask
· Sodium thiosulphate (different concentrations)
· Hydrochloric acid (same concentration each time)
· Water (different concentrations)
· Stop watch
· Paper with black cross on it
· Small memiscus'
· A large memiscus
Method
Firstly, we drew a black cross on a white piece of paper. Then, we put
10 cm³ of hydrochloric acid in a conical flask (measuring the HCL with
a small memiscus), and then put the conical flask on the black cross
on the paper. We then added 50 cm³ of sodium thiosulphate to the
hydrochloric acid, and at this time we do not need to add any water.
Then, we started the stopwatch.
We waited for the black cross to be completely hidden by the
mixture. When this happened we stopped the stopwatch. By this time the
mixture was completely clouded. Then we recorded what the time was.
We then emptied out the contents of the conical flask, and
cleaned it out, and dried it. Next, we added 45 cm³ of sodium
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on the paper. We then added 50 cm³ of sodium thiosulphate to the
hydrochloric acid, and at this time we do not need to add any water.
Then, we started the stopwatch.
We waited for the black cross to be completely hidden by the
mixture. When this happened we stopped the stopwatch. By this time the
mixture was completely clouded. Then we recorded what the time was.
We then emptied out the contents of the conical flask, and
cleaned it out, and dried it. Next, we added 45 cm³ of sodium
thiosulphate; we kept the HCL acid constantly at 10 cm³. Now, because
we have to keep the volume the same for it to be a fair test, we added
5 cm³ of water. (We had to add the sodium thiosulphate and the water
at the same time for this to be a fair test also). We then recorded
the time for the cross to become completely hidden.
We repeated this many times, adding different amounts of sodium
thiosulphate and water each time, and recording the time taken each
time.
Diagram
(SEE ATTACHED SHEET)
Fair test
To make this experiment a fair test, we need to make sure we do a
number of things.
In this experiment we are trying to find the rate of reaction
using concentration as a factor, so there is a number of things we
need to make sure we do to keep it a fair test.
Firstly, we need to keep a chemical at a constant
concentration. So, in this experiment we have chose to keep
hydrochloric acid at a constant concentration. We could have, however,
used sodium thiosulphate as a constant, but we had chose to use
hydrochloric acid.
Next we must make sure that the solution is kept at a constant
volume throughout the experiment. If the volume is different, then it
could give different results to if it was at a constant volume.
We must also make sure that we add both the water and the
sodium thiosulphate at exactly the same time (into the conical flask
with the hydrochloric acid in it), or it could effect the results of
the experiment.
We must start the stop watch at the exact time as we put the
water and the sodium thiosulphate into the conical flask. To do this
it is a lot easier if there are two people doing the experiment, so
one person can put the two substances in the HCL, and one person can
start the stop watch.
Another thing we must do is to make sure that the conical flask
is completely clean and free of any water or any other substance
before we attempt to start the next experiment.
Safety
There are a lot of safety issues we must abide by in this experiment
also.
We must remember that the substances which we use in this
experiment can be very harmful if used the wrong way.
When we do this experiment, it may be necessary to wear safety
goggles, as things are very unpredictable, and even though it is very
unlikely that the solution would come out of the conical flask during
the experiment, one must still be cautious of spills.
We must make sure that coats and bags are all out of the way
while doing the experiment. Ties and hair should be tucked out of the
way, so they do not make contact with any of the chemicals. It would
also be preferable to wear a scientific apron, however this is not
essential.
We should also try our best not to spill any chemicals, and we
must not eat or drink in the lab while dealing with these harmfull
chemicals, as they can get on to our hands.
Prediction
I think that the higher the concentration we use of sodium
thiosulphate, the faster the reaction will happen.
The reason I think that this will happen is because, in a
reation particles collide to give the end results of the reaction. So
if there is a higher concentration of particles on a solution, then
there will be a high number of collisions. If there are a high number
of particles colliding, then there is a higher chance of them
reacting.
Results
Table of results
1^st try:-
Sodium Thiosulphate
Hydrochloric acid
Water
Time taken
50
10
0
48.85
45
10
5
45.46
40
10
10
51.06
35
10
15
59.84
30
10
20
109.04
25
10
25
115.27
20
10
30
141.32
15
10
35
219.08
10
10
40
312.53
5
10
45
459.47
2^nd try :-
Sodium Thiosulphate
Hydrochloric acid
Water
Time Taken
50
10
0
45.07
45
10
5
46.99
40
10
10
48.10
35
10
15
57.67
30
10
20
89.17
25
10
25
107.45
20
10
30
134.61
15
10
35
179.81
10
10
40
234.84
5
10
45
347.21
3^rd try :-
Sodium Thiosulphate
Hydrochloric acid
Water
Average Time Taken
50
10
0
47.299
45
10
5
48.04
40
10
10
52.17
35
10
15
58.76
30
10
20
107.88
25
10
25
114.09
20
10
30
142.52
15
10
35
221.26
10
10
40
310.33
5
10
45
449.27
AVERAGES
I have also come up with a set of average results for all 3
experiments :-
Sodium Thiosulphate
Hydrochloric acid
Water
Average Time Taken
50
10
0
47.07
45
10
5
47.10
40
10
10
50.77
35
10
15
58.76
30
10
20
102.63
25
10
25
112.27
20
10
30
139.48
15
10
35
206.71
10
10
40
285.03
5
10
45
418.65
Conclusion
In conclusion I have found that my prediction was correct. The rate of
reaction was quicker when there was a higher concentration of sodium
thiosulphate. This can easily be seen when we look at the results
table.
This may have also have been the same if I had used the
hydrochloric acid as a variable instead of the sodium thiosulphate. It
may have been faster or slower at reacting than the sodium
thiosulphate.
Evaluation
I think that most of the experiment I have done has been fine, with as
little anomalous results as possible. However, there are still a few
anomalous results, which I can point out below:.
Sodium Thiosulphate
Hydrochloric acid
Water
Time taken
50
10
0
48.85
45
10
5
45.46
40
10
10
51.06
35
10
15
59.84
Anomalous Result
This is the only anomalous result that I have recorded. The result may
have turned out anomalous because of basic human error, or maybe
because we measured the substances wrong. It may have even been
because we did not clean the apparatus properly.
Apart from this, the accuracy of my experiment has been more or
less accurate. Although there are a number of ways in which we could
have made the results more reliable. For instance, we could have used
better measuring equipment, because the apparatus we used was mainly
basic equipment.
Another thing we could have done to bring more evidence is to
have tried to use the hydrochloric acid as the variable substance, and
used the sodium thiosulphate as the constant substance. This would
have brought more evidence to support the idea that the higher
concentration of a substance, the faster it will react.
I think that the evidence, which I have received, is enough to
reach a suitable conclusion, but there are a few flaws to the
experiment (which I have mentioned). Apart from them, the experiment
is fine.