Investigate the affect of temperature of sodium thiosulfate and hydrochloric acid against rates of reaction.
Affect of Temperature
Preliminary Experiment
For my first preliminary experiment, I had to investigate the affect of temperature of sodium thiosulfate and hydrochloric acid against rates of reaction. The chemical equation for this is:
Sodium thiosulfate + hydrochloric acid sodium chloride + sulfur dioxide + sulfur + water
Na2S2O3(aq) + HCL(aq) NaCl(aq) + SO2(aq) + S(s) + H2O(l)
The solid sulfur (S(s)) formed in this reaction makes the colourless solution go cloudy.
I used my preliminary results to give myself an idea of which temperature would give me the best results. For my preliminary results, I used 30 cm³ of sodium thiosulfate solution, 5 cm³ of Hydrochloric acid and 20 cm³ of distilled water. The variable that was changed was the temperatures. My preliminary results are in the table below:
Temperature (°C)
Time (seconds)
/ time (s¯¹)
/ time (s¯¹) x 100
22
61
0.016
.6
36
24
0.042
4.2
38
20
0.05
5
39
25
0.04
4
46
7
0.5882
58.82
49
7
0.5882
58.82
54
9
0.0185
.85
71
6
0.1667
6.67
From the table above, I can see that the 71°c temperature produced the best results, because this temperature gave me the quickest reaction time. Therefore, from my results I can say that, the higher the temperature, the faster the collision rate.
There was a systematic error on the 46°c and 49°c temperatures, as they are both the same. From my results, the 49°c temperature should have affected the rate of reaction quicker, because the temperature is higher. I also found an error when I did my 39°c test. The result is 5 seconds slower than the 38°c test. The result should have been 5 seconds quicker with the 39°c test. On my preliminary graph, I can see that the rate of the reaction gets quicker as the temperature increases. There are three anomalous results from my tests. These errors ...
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There was a systematic error on the 46°c and 49°c temperatures, as they are both the same. From my results, the 49°c temperature should have affected the rate of reaction quicker, because the temperature is higher. I also found an error when I did my 39°c test. The result is 5 seconds slower than the 38°c test. The result should have been 5 seconds quicker with the 39°c test. On my preliminary graph, I can see that the rate of the reaction gets quicker as the temperature increases. There are three anomalous results from my tests. These errors could have occurred due to delays in stopping the timer on time and reading the time off it incorrectly.
The Real Experiment
For my real experiment, I used the following:
* 40 cm³ of Sodium Thiosulfate solution
* 30 cm³ of Distilled water
* 10 cm³ of Hydrochloric acid
* Specific temperatures - 25°c, 35°c, 45°c, 55°c, 65°c, 75°c, 85°c and 95°c.
I changed the amounts of the thiosulfate solution and hydrochloric acid in order to see if my real results would be any different from my preliminary results. I also changed the temperatures because the temperatures in my preliminary tests were erratic and did not follow any sequence, but the temperatures that I have chosen in my real tests have a steadily increasing sequence to them. They all have the same gap between each other of 10°c starting at 25°c. This should reduce the mistakes in my preliminary experiment because I have chosen a more
Apparatus Used
* 3 beakers
* Tripod
* Gauze
* Bunsen burner
* Mat
* Conical flask
* Thermometer
* A4 paper
* Stopwatch
The Method
* Get 40 cm³ of sodium thiosulfate solution, 30 cm³ of distilled water and 10 cm³ of hydrochloric acid (HCL).
* Put each solution into a different beaker and label them.
* Get the tripod, place the gauze on top of it, and then place the Bunsen burner underneath it. Place the Bunsen burner on top of the fireproof mat.
* Put the water and thiosulfate solution into a conical flask and heat to a chosen temperature. Keep the acid away from the Bunsen burner, as this could start a fire. Choose a temperature by using a thermometer. Make sure you wear goggles, as this is a safety issue.
* While your partner watches the temperature and gets it to the chosen one, you draw a circle (the same width as the conical flask) and draw a cross on it.
* Once the thiosulfate solution and water have both been heated to a certain temperature, place 10 cm³ of HCL into it and quickly put it over the circle with the cross in the middle of the circle. This is important as the solution could react straight away and therefore could end up as a false result.
* Start the clock.
* Record the time it took to make the cross invisible.
* Repeat experiments using different temperatures.
The Things That Must Be Kept Constant
* The concentration of the thiosulfate solution because the more molecules there are, the more collisions there will be (according to the collision theory). If I keep the solution the same, then every experiment has an equal chance and this means I have a fair experiment.
* The concentration of the HCL solution, because again, the more molecules there are, the more collisions there will be. This will mean a greater chance of a successful reaction.
* I must use the same beaker all the way through, because different beakers have different surface areas and this will result in an unfair experiment.
* I must measure the temperature of the thiosulfate solution at the same point in each experiment - before I add the acid.
* I must use the same cross, as one cross could have a darker shade that another. This means that the darker shaded cross would be visible for longer.
* The same person must watch the cross disappear in the experiment, as different people have different eyesight.
My Results
I would expect the 75°c temperature to have the best result, as it is a higher temperature and therefore should have a quicker reaction rate.
Temperature (°C)
Time (seconds)
/ time ( s¯¹)
/ time ( s¯¹) x 100
25
48
0.02
2
35
31
0.03
3
45
20
0.05
5
55
2
0.08
8
65
7
0.14
4
75
3
0.33
33
From my table below, I can see that the 75°c temperature produced the best results, because this temperature gave me the quickest reaction time and therefore, this means that 75°c test is the highest temperature that I can go up to before the sodium thiosulfate solution begins to decompose. Once the solution began to decompose, it was too difficult to measure the time it took for the solution to turn cloudy because the reaction was too quick for me to measure.
My Graph
From my graph, I can say that there is an exponential relationship between the temperature and reaction rate, in the sense that for every 10°c rise in temperature, there is an increase in the reaction rate by about 60%.
My Conclusion
From my experiment, I can say that as the temperature of the sodium thiosulfate solution increased in both experiments, the time taken for the reactions to complete decreased. The rate of increase appeared to be 60% faster for every 10°c rise in temperature, although I expected the rate of reaction to double.
