Science Rates of Reaction

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Reaction Rate Coursework

Aim
To see how the concentration of a reactant affects the rate of reaction, in this case sodium thiosulphate and acid.

Scientific Background
For a reaction to occur, the particles of the reactants must be colliding with each other with enough energy, the amount of energy needed for the reaction is called activation energy. Activation energy is altered by temperature, concentration, surface area of and the pressure on the reactants. Stirring the reactants also increases the rate of reaction because the particles are travelling at a higher speed therefore less time will be taken for a sodium thiosulphate molecule to collide with an acid molecule.

Prediction
As the concentration of sodium thiosulphate increases, the time it takes for the reaction to complete will decrease, less with each higher concentration.

Fair Test
Because this experiment is only conducted to see how the concentration of a reactant affects the rate of reaction, other variables must be kept the same for it to be a fair test: the same person is going to watch the reaction; a thermometer can record the room temperature to make sure that it’s consistent throughout the experiment; the other variables will stay consistent without interferences; none of the reacting solutions will be stirred.

Equipment List
2.Large beaker
3.2 small beakers
4.Large measuring cylinder (25ml)
5.Small measuring cylinder
6.Dropper
7.Flask
8.Stop-clock

Method

9.Write ‘water’, ‘sodium thiosulphate’ and ‘acid’ across a piece of paper then draw a shape. 10.Fill up the large beaker with sodium thiosulphate and place it over the word on the paper. 11.Fill up one of the small beakers with acid and the other with water then place each over its word on the paper. 12.Fill up the large measuring cylinder with 25ml of sodium thiosulphate, use the dropper for corrections. 13.Use the dropper to fill up the small measuring cylinder with 2ml of acid. 14.Pour sodium thiosulphate into the flask; place it over the shape on the paper. 15.Pour the acid into the flask, start the stop-clock at the same time. 16.Watch the mixture until the shape underneath it cannot be seen, stop the stop-clock at the same time. 17.Record the time in seconds in a table.

18.Wash out the flask and place it back over the shape.
19.Work out the next concentration of sodium thiosulphate and fill up the measuring cylinder with that amount. 20.Add water to the sodium thiosulphate until it fills up to 25ml. 21.Use the dropper to fill up the small measuring cylinder with 2ml of acid. 22.Repeat steps 7-10.

23.Repeat the same process for all the other concentrations.

Results Tables

Trial Run Results:

Reaction time(sec)

1st Try
2nd Try
Average
75%
46.46
52.37
49.665
50%
73.50
72.96
73.23
25%
189.82
199.22
194.52

Results Table (1st attempt):

Reaction time(sec)

1st Try
2nd Try
Average
100%
40.43
42.50
41.465
90%
59.56
43.32
51.44
80%
71.59
60.43
66.01
70%
73.32
63.84
68.58
60%
78.15
62.22
70.185
50%
86.37

86.37
40%
137.27

137.27
30%
189.12

189.12

Results Table (2nd attempt):

Reaction time(sec)

Repeats

1st
2nd
3rd
4th

100%
38.68
32.02
34.17
47.24
35.59

35.115
90%
47.87
47.09
47.01

47.323
80%
44.37
46.41
47.06
43.75
38.56
44.01
41.68
43.691
70%
62.75
48.12
47.64
48.96

48.24
60%
51.63
55.78
55.64
52.63
58.84

54.904
50%
60.72
60.06
72.56
70.36
65.82

65.904
40%
83.38
95.34
87.01
80.41
89.37
80.56
98.06
87.733
30%
135.32
142.37
138.56
158.15

138.75
20%
235.22
238.06
176.56
236.18

236.487
(Bold numbers in italics are outliers)

Conclusion (Results evaluation for prediction)

The results from the trail run proves the prediction to be right; the results from the second attempt also fit in quite well with the prediction, except for the 90% concentration which was probably a mistake. However, the results from the first...
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