Investigating the Rate of Reaction between Sodium Thiosulphate and Hydrochloric Acid

. Set up the equipment as shown in the diagram.

2. Heat the water bath using the Bunsen burner until it begins to boil.

3. Use two pipettes to withdraw 10cm³ of each chemical and add them into the two separate boiling tubes.

4. Place the boiling tubes into the water bath and place the thermometer into one if the boiling tubes.

5. When the thermometer reaches twenty degrees take out the two boiling tubes and pour the sodium thiosulphate into the beaker which is above the cross.

6. Then pour in the second chemical, as soon as the two chemicals touch start the stop watch.

7. Time how long it takes for the cross to disappear.

8. Repeat the experiment for 25, 30, 35, 40, 45 and 50 degrees. Do not contaminate any of the glass wear.

Results:

Trial

Start Temperature (°c)

End Temperature (°c)

Average Temperature (°c)

Time (seconds)

Average Time

Rate of Reaction 1/t (4 d.p)

Rate of Reaction x100 (2 d.p)

One

0

0

0

27.8

26.9

0.0079

0.79

Two

0

0

26

One

5

6

7

68.4

69.9

0.0143

.43

Two

6

7

71.4

One

21

22

22

63.8

63.5

0.0157

.57

Two

20

23

63.2

One

25

25

25

44.2

45.4

0.0221

2.21

Two

24

26

46.6

One

30

32

32

33.4

32.6

0.0306

3.06

Two

32

32

31.8

One

35

34

35

8.1

8.3

0.0546

5.46

Two

35

34

8.5

One

39

35

37

22.7

23.4

0.0427

4.27

Two

38

36

24.1

One

48

47

48

3.9

4.9

0.0671

6.71

Two

48

48

5.9

One

50

50

50

3

4

0.0714

7.14

Two

51

49

5

Discussion of Results

* It is clear from the graph that as the temperature increases the rate of reaction also increases. You can also see that the line does not go through the origin this is because the two chemicals are both still liquid at zero degrees this means that particles are still colliding causing a slow reaction to take place because the particles are colliding with little energy. I took readings at zero degrees so the position where the line crosses the y-axis is accurate.

* In the first few readings the rate of reaction increases at a slow rate but gradually the rate of reaction begins to increase quicker. You can see this because the gradient becomes gradually steeper.

* After the chemicals reach one hundred degrees the water in the chemicals will begin to evaporate this will increase the concentration of the two chemicals causing the reaction to occur slightly quicker making the results inaccurate so I am unable to extrapolate beyond the range of data because the prediction will be inaccurate.

* The results relate to the collision which I have mentioned earlier it states that when reactions occur the particles of the chemicals collide and some of the collisions result in reactions. By increasing the temperature I am providing the particles with more energy this causes them to move around faster and collide with more energy this results with more reactions occurring more often as my results show.

Conclusion:

Looking at my results it is clear that as the temperature increases the rate of reaction also increases. The graph also becomes steeper as the temperature increases this is because the increase in the rate of reaction rises. However it does not rise proportionality to the temperature. My hypothesis was correct.

Evaluation

I believe the data which I obtained in the experiment is reliable because I have taken a number of steps to increase the accuracy and reliability of my results. I have used pipettes instead of measuring cylinders to increase the accuracy of the amount of substances measured out and I have also increased the accuracy of the temperature reading taken as well. I believe that the evidence obtained is sufficient to support the conclusion that as the temperature increases the rate of reactions also increases. However I have spotted an anomaly which shows up obviously on my graph. It is at (37,4.27) however this result should not really be counted because when this reading was taken the beaker which I poured the two chemicals into was not the same as I had used for the previous readings because it had been mislaid. However after that particular reading I managed to find the beaker which I had used before but unfortunately I did not have enough time to retake that the reading but I am confident that if I did retake it, it would fit in with the line of best fit on the graph.

I believe that the procedure itself is flawed this is because as the temperature of the chemicals the water within them will evaporate and therefore increase the concentration of the chemicals and in turn increase the rate of reaction. If this does occur it would cause all of the readings to increase by a relatively small amount and there for make them slightly inaccurate. These readings would make the graph slightly steeper than it should be. However there is another factor which will also alter the graphs shape. This is temperature because I found that when the chemicals were cooled below room temperature the resulting temperature after the reaction had taken place would be slightly higher than what I started with. This is the reason I chose to take the average temperature instead of just the start temperature. I also found that all of the temperatures taken above room temperature would fall slightly. I also found the fall in temperature would increase as the temperature increased. When these factors are taken into consideration it becomes clear that the graph should be altered accordingly. These two factors each affect the graph in the opposite way. So in order to predict what the graph should like I must work out which these affects the graph the most however I cannot tell which factor has the greatest affect upon the data the only way to tell would be to carry out further work.

However if I was to repeat this experiment there are certain steps I could take to reduce these factors. In order to reduce water loss, cling-film could be applied to the boiling tubes this would catch the water and prevent it from escaping, however this method would make it hard to take the temperature of each chemical so instead of a water bath an electronic water bath could possibly be used this can be set to a certain temperature and the boiling tubes could be left in them for a particular time until they have reached the required temperature. This I believe would help solve the concentration problem.

In order to stop the temperature loss the best way would be to constantly heat or cool the chemicals while they are reacting this would help prevent the temperature from changing so much. In order to cool the chemicals ice would be applied round the side of the beaker this would hopefully help cool it. To heat the chemicals while they are reacting would be very difficult. I believe that the method which was used in the experiment was not very accurate. I found that it would be difficult to tell exactly when the cross had vanished. Looking at the chemical equation I noticed that sulphur gas was given off, I think that a much more accurate method would be to measure the amount of gas produced when the chemicals react together. If a boiling tube had a delivery tube connected to it the chemicals could be poured in and the gas would be bubbled into a burette. This would also allow the chemicals to be constantly heated easily.

Despite all of these flaws in the experiment I still believe that the results do support my conclusion and that the graph itself is relatively accurate. The one anomaly which occurred can easily be accounted for and I do heavily believe if that reading was retaken it would fit with the trend of the rest of the data.

Further work to investigate the rate of reaction could be to test the other factors which affect the collision theory. Experiments could be carried out to see how greatly pressure affects the rate of reaction; the same two chemicals would be put under different pressures and the time for the cross to disappear taken. Or possible the concentration of the chemicals could be increased this would cause there to be more particles in the chemicals and therefore more collisions occurring. The rate of reactions of 1-5 mole chemicals could be taken and this would give an idea of how concentration will also affect the rate of reaction. Another possible extension would be to use different chemicals in the reaction instead of sodium thiosulphate; potassium thiosulphate would be used after this evidence is obtained the two for sodium thiosulphate could then be compared with the graph of potassium thiosulphate. Instead of these extensions other acids could be used nitric and sulphuric acid could be used in the same experiment and then the graphs obtained would be compared.