ensure by using measuring apparatus.
I will have to keep the temperature constant for all my experiments. If I do not, the
temperature will cause more collisions because all the particles will be moving faster and
hitting each other which will break more bonds. I will control the temperature by measuring
it using a thermometer in the solution. If I had the equipment I would use a water bath but
there is not enough equipment available for every student.
I will have to keep the amount of stirring constant. If I do not it will change my set of results.
I will keep the amount stirring the same by stirring at a steady speed until I cannot see
through the solution.
I will have keep my apparatus the same. This will ensure a fair test. I will use the same
beaker and all other items for all my experiments.
I will have to keep the volume of the whole solution the same. If I do not it will not ensure a
fair test.
A catalyst would affect the experiment but I will not be using one in my experiment.
The pressure and surface area will not affect the experiment.
Number of experiments
I will be performing seven readings. The range will be from 10-40 cm3 of sodium
thiosulphate and from 0-30 cm3 of water. The amount of hydrochloric acid will remain
constant at 10 cm3. I will repeat the experiment five times. By repeating the experiments it
will give me better results which will be more accurate. If anything goes terribly wrong in
one of the repetitions of my experiment I will repeat it to get a more realistic and accurate
result.
Trial experiments
I will be performing some trial experiments. By doing this it will tell me what
problems I may have with my experiments. Therefore I can rectify them and make my
experiments more accurate and precise.
In this trial experiment I have learnt that when using a large conical flask the time is a
lot greater than when using a small conical. For example; I had 10cm3 of sodium
thiosulphate, 30cm3 of water and 10cm of hydrochloric acid. When using a large conical
flask the experiment took 9 mins 35 seconds whereas it took 2mins36 seconds with a small
conical flask. So therefore I am going to use a small conical flask to ensure my results are
faster and my results will be more accurate over a smaller time.
Method
1.Before you start you must ensure that you wear a lab coat and safety glasses.
2.Take a measuring cylinder (size dependant on amount needed.) Measure out amount of
sodium thiosulphate needed
3.Put measured out sodium thiosulphate in into a 100cm3 conical flask.
4.Measure out amount of distilled water needed into a measuring cylinder.
5.Add distilled water into the sodium thiosulphate.
6.Measure out needed amount of hydrochloric acid into a different measuring cylinder.
7.Place 100cm3 conical flask directly above a piece of paper with a cross on it.
8.Have a stopwatch ready for use.
9.Add the hydrochloric acid to the sodium thiosulphate and distilled water solution.
10.Press start on your stopwatch.
11.Stir the mixed solution at a steady speed until you cannot see the cross through the
solution.
12.When you cannot see through the solution press stop on the stopwatch and record your
answer.
13.Pour the solution down a fume cupboard and rinse and clean the conical flask so it is fit
for use for the next experiment.
14. Now repeat the experiment 5 times.
List of Equipment
1. 100cm conical flask
2. 50cm measuring cylinder
3. 25cm measuring cylinder
4. Stopwatch
5. Thermometer
6. Dropping pipette
7. A cross on a piece of paper
8. 1.0 M hydrochloric acid
9. 40g/l sodium thiosulphate
10. Distilled water
11. Fume cupboard for waste products.
12. Safety glasses
13. Lab coat
Prediction
In my experiment I predict that when I increase the concentration of sodium
thiosulphate the rate of reaction will also increase. When I decrease the concentration of
sodium thiosulphate the rate of reaction will decrease. When I double the concentration of
sodium thiosulphate the number of particles will also double in every cm3. Therefore the
amount of collisions will double per second and therefore the amount of successful collisions
will double, and also the rate of reaction will double.
Evaluation
Looking at my results and my graph the results shown were fine on the
whole. From my graph there were a few points that were off the line but only slightly. These
points were shared out equally on either side of my line of best fit, which was good. During
my investigation there were a few problems which may of affected my results. The graph
trend was a straight line which was what I expected, because as the concentration of
sodium thiosulphate doubles the rate doubles. Therefore it means that graph will stay
constant and make a straight line.
After a couple of experiments consecutively, the conical flask got slightly cloudy
after washing it out. This will therefore make the times shorter and shorter than they should
be after more and more experiments because there was a layer of cloudy solid, which I
could not get rid off after washing it out. If I repeated the experiment I would of cleaned it
out properly every time and dry extremely well to make sure that that would not affect my
results. During my experiments I could not change the flask even though it was cloudy, the
reason being was that changing the flask would of made it an unfair test and therefore may
of jeopardised my results.
The temperature was also another problem that I had. The thermometer I
used was not at all very accurate. It was hard to tell if the temperature changed at all. If the
temperature did change that would of affected the results as they did but at a slight. If I
repeated the experiment I could of used a controlled thermostat heater which would of
made sure the temperature stayed the same.
I should of kept the amount of substance each time. I could not do this mainly
because of the equipment I had. The equipment used was not of the greatest standard. If I
had more accurate equipment that would of ensured being much more precise.
Controlling the amount of stirring was also a problem. It was hard to get the amount
and force of stirring the same every time. This may of affected my results slightly. If I had
the equipment I would of had it stirred in a automatic machine ensuring this would be the
same each time. If I repeated the experiment and I had the resources I would of stirred the
solution in an automatic stirrer for the right amount of time and at the right force every time.
This would of ensure that my results were not affected.
Seeing when the cross disappeared was quite hard. To ensure you got precise
results you would have had to kept the level of your eyesight the same every time and make
sure are concentrating without any distractions. This was quite a big problem for me
because some of the time it was hard to notice when the cross had totally disappeared and
this could have affected my results. If I repeated the experiment again I could of had a
microscope set up at the right level and height to make sure that you could be precise about
when the cross disappeared, I would keep the level and height of the microscope the same
every time.
Time was another pressure put on me. During experiments I was rushing quite a lot,
therefore when I was measuring out my solutions they may not of been perfect, when
washing up equipment the might not as been thorough as I would like them to be. So, if I
had more time I could of taken my time get everything perfect and produce some excellent
results.
During my experiments there was an anomaly. One of my experiments took
118.39secs, whereas the rest of experiments in that group took roughly 130secs. I spotted
before I plotted my graphs and worked out my averages. I then repeated this experiment a
couple more times to see if I could get better results which would of made my results
perfect. The repeated results were 134.19 and 124.39. these results were much more
consistent and they coincided with the rest of my results.
If I repeated the experiment I would investigate another factor which could affect
the experiment. I would investigate changing the concentration of hydrochloric acid.
I would investigate this to see what results I may get by changing a different factor. I
would change the concentration of the hydrochloric acid and change the amount of water
accordingly and I would keep the amount of sodium thiosulphate the same. Whilst doing all
this I would keep the total amount of solution the same throughout.
This is a table to show how I would do this experiment
AmountofHydrochloricAcid(cm3) 40 35 30 25 20 15 10
AmountofWater (cm3) 0 5 10 15 20 25 30
AmountofSodiumThiosulphate(cm3) 10 10 10 1 10 10 10
TotalAmountofSolution(cm3) 50 50 50 50 50 50 50
I predict that by increasing the hydrochloric acid the rate of reaction will decrease.
When I double the amount of hydrochloric acid the number of particles will halve in every
cm3. Therefore the amount of collisions will halve per second and therefore the amount of
successful collisions will halve, and the rate of reaction will also halve.
If I decrease the hydrochloric acid the rate of reaction will increase. When I
decrease the amount of hydrochloric acid the rate of reaction will increase. When I halve
the amount of hydrochloric acid the number of particles will double in every cm3. Therefore
the amount of collisions will double per second and therefore the amount of successful
collisions will double, and the rate of reaction will also double.