Rates of Reaction - The concentration of hydrochloric acid and the rate of reaction with sodium theosulphate

Rates of Reaction - The concentration of hydrochloric acid and the rate of reaction with sodium theosulphate

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Rate of Reaction

After doing my pilot run, i think that my method and apparatus used
should be mostly the same:

Apparatus - 1 conical flask

- 1 lamenated 'x'
- 3 test tubes
- 1 thermometer
- 1 stop watch
- 3 pipettes


1. Measure 10ml of 0.2mol/dm3 or 0.2moldm-3 sodium

2. Pour it into the conical flask

3. Add 40ml of distilled water for dillution.

4. Then add 5cm3 of dilute hydrochloric acid of concentration
2mol/dm3 at room temperature

5. Record the temperature of the mixture. Stir mixture gently.

6. Stir mixture gently

7. Start time when all is stirred and when the conical flask is
over the 'X' paper.

8. Once the cross is completely out of sight due to the reactionof the
sodium thiosulphate and hydrochloric acid and then record the time.

9. I willl then repeat this with different measurements of sodium
thiosulphate and water.

Changes I have made and why

- I am not going to be using a burette because after finishing my
pilot run, i realised that i was gradually getting more and more
behind schedule and I wouldn;t have enough time to complete my
obtaining evidence if I were to carry on using it.

Fair test

To make sure it was a fair test. i had to constantly keep cleaning and
washing the equipmentas any remaining substances can cause major
differences in the results. And we had to try ansd hope that the room
temperature will remain constant during the course of my experiment.
Also we always have to keep the volume of concentrstion the same -

number and range of experiments

- If I have enough time, I would like to try around nine different
concentrations of sodium thiosulphate with water. I am going to
try hte following volumes of sodium thiosulphate: 10ml, 15ml, 20ml,
25ml, 30ml,35ml, 40ml,45ml and 50ml.

- I have chosen a range of 40ml as I think this is enough to truly
experience the various actions of sodium thiosulphate reacting with
hydrochloric acid.

- If any of my results seem somewhat innaccurate or faulty, I will try
my best to redo them.


- Make sure to tie hair back.
- Wear a lab coat.
- Wear safety glasses or goggles.
- Wash hand in between each experimewnt and after anmd before eating.
- Open windows so the smell isn't too overwhelming


To make my experiment a fair test, we must always have the same volume
of solutions, 55ml.

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This is because otherwise, with different volumes
we are not concentrating or properly investigating the correct task.
Our volume of 55ml consists of 5ml or hydrochloric acid and a mixtue
of sodium thiosulphate and water always adding up to 50ml. Now, when
looking back to the table of dillutions in my planning, it should
hopefully make more sense then before.

After finding out my first set of results I realised that I could only
tell that my results were acurate if you compare it to itself and that
the order from the longest time to the shortest time turned out how i
had predicted, but still I was not sure that it was right.

So, after contemplating it, I realised I would have to do a whole
other set of results as repeats. So after doing this, I had two times
for each concentration of sodium thiosulphate, and therefore I should
be able to work out accurate averages for the rate of reaction and
average time of each concentration of sodium thiosulphate.



When first looking at my results with out the help of any graph. I
think that my results look fairly accurate, this is only because, in
my prediction I had said that the experiment with the most sodium
tiosulphate, 50ml, would be the fastest to react and from there the
time would get gradually longer and longer, meaning that the
experiment with the least sodium thiosulphate, 10ml, would take the

I shall now display graphs for both the rate of reaction and for the
time in seconds.



When looking at my line graph of average times with different
concentratiojns of sodium thiosulphate. It looks like all my results
are fairly accurat as my curve of best fit seems to run smoothly
through all the points. So therefore it gives out the impression that
there are no anomalies.

However, when looking at my graph of the average rate of reaction with
different concentrations of sodium thiosulphate. There are four
anomalies. event though these anomaliesare not big they do not fit
with the curve of best fit which seems to run through all the other
points. The four anomalies appear to be at 20ml,25ml,30,land 35ml.

My prediction was rather right when saying that as the concentration
doubles the reaction rate also doubles, I was also right when I said
that they will be directly proportional.Un fotuantely I had the wrong
idea of what the graph would look like as I thought my results, when
drawn on a line graph, would be a straight line, but no, in fact it is
a curve. I also got another graph wrong, also displaying the time it
took until teh cross could no longer be seen. IO had predicted this
one the wrong way around. I have shown in this graph that with 0ml of
sodium thiosulphate the reaction will be the fastest, whereas really
it is the other way around.

My anomalies could have been caused by one set of results going very
wrong and therefore it will effect my average. So now I will
investigate to find out if one of my sets of results rendered the
average to be an anomaly.


After looking at both of the experiment's rate of reaction graphs, I
can see that both of them contributed to my anomalous results, the
anomalies in my first experiment are 25ml, 30ml and 35ml. And the
anomalie in my second experiment are 20ml, 25ml, 30ml, 35ml and 40ml.
I think that the second experiment was more the cause of my anomalies
because it has five anomalies which are mostly very innacurate,
whereas my first experiment has only three anomalies which lie closer
to my curve of best fit.

I also think that my accurate result of 40ml in the first set evens
out my inaccurate result in the second set and make it an average
which lies on my curve of best fit. In turn I also think that my
inaccurat result of 20ml in the second experiment causes my accurate
result in my first experiment to become an anomaly.


I think that my method gave reliable evidence showing that my overall
prediction was fairly accurate. The results that do not seem to fit in
with everything are: 20ml, 25ml, 30ml and 35ml results. These are
rather a lot of anomalis and I definatley regret not being able to do
more repeats again on this. I think these anomaliescame to place
because of my second experiment which was very different to the first.
This could be because the room temperature was different on different
days, or it could have been thatthe thermometers we used measure to
plus or minus 1 degree celsius of the actual temperature.

These anomalies could also have come about due to my judgement of whne
the cross was out of sight, I am only human so I have to guesstimate
when I thought the solution was the right color.

If I could go back to my experiment again I would have re-done all my
experiments to triple check that they are accurate and hopefully more
precise averages. I would also have used a burette not a measuring
cylinder and test tubes to measure volumes with the burette. I also
would have preffered to use a more accurate thermometer as I have said
ours isn't very accurate at all.

I found it very hard to judge when the solution caused the cross to
appear gone because the exeperiments were on different days and
sometimes the lighting was different causing me to see the experiment
in different ways over the span of two weeks.

I think that my method gave evidence that it is very reliable, however
in this case I think it was the environmental fctors that caused my
results to go askew.
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