water and 5cm3 of Hydrochloric acid the reaction happened in 25seconds when
using the 2moler acid, 31seconds when using the 1moler acid and 43 seconds when
using the 0.5moler acid. The rate of reaction got slower as there were less
collision between the hydrochloric acid and thiosulphate because the
concentration of the acid got less. When we changed the concentration of the
sodium thiosulphate to 40cm3 to 10cm3 of water then add the same amount of
hydrochloric acid (5cm 3), the rate of reaction was slower. The 2moler of acid
took 231seconds for the cross to disappear. It took 310 seconds for the cross to
disappear in the 1moler acid. For the 0.5moler acid I didn't get a result, as it
took too long. We used the preliminary experiment to find a suitable
concentration of acid. I used my results from my preliminary experiment to get
my prediction of the more thiosulphate to water will make the rate of reaction
quicker and the cross with disappear in a shorter time, to the solution with
more water to sodium thiosulphate. I also predict that the double the strength
of thiosulphate to water, the rate of reaction will be double as quick, as there
are double the amount of thiosulphate particles to cause a reaction with the
hydrochloric acid.
Concentrations: which I am going to use.
Hydrochloric Acid(cm3) Sodium Thiosulphate (cm3) Distilled Water(Cm3)
5 50 10
5 40 20
5 30 30
5 20 40
5 10 50
Fair Test and Safety
I made my experiment fair by using the same bottles of sodium thiosulphate and
hydrochloric acid each time as the concentration in each bottle mite vary and
could change my results. I used distilled water every time, as normal tap water
has chemicals in which could also change my results. I made the volume of water
and thiosulphate the same each time. I also had two measuring cylinders one for
the thiosulphate and water and the other for the hydrochloric acid. As a safety
measure I wore glasses so that I didn't get any hydrochloric acid in my eyes by
mistake. Also when the cross (used the same piece of paper with a cross each
time) had disappeared I got rid of the solution as quickly as possible so I
didn't inhale too much of the sulphur dioxide. I used the same flask each time
but washed it out thoroughly.
Apparatus
Stop Clock,
2 Measuring cylinders,
1 Flask,
1 bottle of Sodium Thiosulphate,
1 bottle of Hydrochloric acid,
I bottle of Distilled Water,
A stop clock,
Safety glasses,
A piece of paper marked with a cross.
Method
Ÿ Collect all the apparatus needed.
Ÿ Put on the safety glasses before starting the experiment.
Ÿ Measure out 50cm cubed of sodium thiosulphate in to the flask
Ÿ Then measure out 5cm cubed of Hydrochloric acid.
Ÿ When adding the hydrochloric acid to the sodium thiosulphate in the flask,
immediately start the stop clock.
Ÿ Swirl the flask 3 times to mix, then place the flask on top of the paper with
the cross.
Ÿ Watch the cross from above. As soon as the cross disappears stop the stop
clock.
Ÿ Record the time in seconds, it took for the cross to disappear.
Ÿ Pour the mixture away as quickly as possible (so not to inhale the fumes)
Ÿ Wash out the flask.
Ÿ Restart the stop clock to start again with the next concentration using
distilled water to make up the volume.
Obtaining Evidence
Volume of Thiosulphate solution Cm3 Volume of waterCm3 1st expt. Time taken for
cross to disappear in seconds 2nd expt. Time taken for cross to disappear in
seconds Average time taken in seconds
50 0 32 28 30
40 10 39 41 40
30 20 55 51 53
20 30 103 91 97
10 40 328 296 312
Table to find the rate of reaction
Volume of Sodium thiosulphate Cm3 How to get the rate of reaction? Rate of
reaction
50 1/30 = 0.033 33x10-3
40 1/40 = 0.025 25x10-3
30 1/53 = 0.019 19x10-3
20 1/97 = 0.010 10x10-3
10 1/312 = 0.0032 3.2x10-3
Graphs to show the line of best fit on graph paper
Analysis of Evidence
What I can see from my results is basically the more thiosulphate to water the
quicker the rate of reaction happens and the cross disappears. From the graphs I
can see that the average time in seconds is much sorter and under a minute when
the thiosulphate when is more than the water. Which is for the first three
readings. After that the time taken gets much longer when the ratio of water to
thiosulphate is bigger. I didn't have any anomalous results from my experiment,
which means that the measurements must have been precise. What I predicted was
right to the out come of my experiment, as I predicted that the bigger the ratio
of sodium thiosulphate to water the quicker the cross would disappear from eye
sight. Which means the rate of reaction is quicker. Why this happens is because
the more thiosulphate to react with hydrochloric acid makes the reaction happen
quicker, because the greater the ratio of thiosulphate particles to collide with
the hydrochloric acid particles the quicker the rate of reaction is. This is
what I predicted to happen. The first three results that I got the time taken
for the cross to disappear was under a minute, but after that were the ratio of
water is greater then the sulphur thiosulphate the time taken becomes much
longer. This happens because there is more water so less particles of
thiosulphate can react with the hydrochloric acid, and make sulphur, which makes
the solution cloudy.
Evaluation
For this experiment changes I would have made would have been to use more
accurate equipment for measuring the Sodium thiosulphate, water and the
hydrochloric acid. I would have chosen to use a burette or a pipette, which
would ensure that I wouldn't get any anomalous results. Also if I could do the
experiment again I would find a better way of finding out when the solution
turned totally cloudy so that light can't pass through it. Maybe if we used a
light and a light sensitive device to tell when the solution is totally cloudy
that would make the experiment more accurate.
The way we conducted the experiment was not very precise as I was not always
sure when the cross had completely disappeared and the stop clock was not always
stopped exactly when I thought the cross was out of sight. I think that the
whole experiment should have been carried out again because we did not always
use the right pipette with the right solution, which probably affected the
results in some way.