Factors which affect the rate of reaction between dilute hydrochloric acid and sodium thiopsulphate

A dilute solution (i.e.: less particles of sodium thiosulphate)

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These collisions can be related to the particle collision theory. The particle collision theory states that

"The more molecules there are the frequency of succesful collisions is greater and therefore the reaction rate is speeded up"

so when water is added to the concentrated solution it makes it even harder for the solution to react, redulting in a longer time taken for the whole reaction to take place.

I am going to make the experiment a fair test by:

* Keeping the volume of hydrochloric acid the same

* Using clean experiment

I am going to make the experiment safe by:

* Wearing goggles

* Being sensible

* Using correct & safe equipment

Method:

* Measure out the correct volume of dilute hydrochloric acid (a constant measurement of 10ml) and sodium thiosulphate (a measurement of 25ml going down 2.5 ml every time) and water (Going up 5ml every time) into measuring cylinders. The increase of water dilutes the concentrated solution more and more every time, making the reaction a lot harder to happen.

* Place the beaker on top of a black cross (drawn on paper) and pour both dilute hydrochloric acid and sodium thiosulphate (and water later on) into the beaker at the same time. Start the stopwatch and start stirring.

* When the solution has gone cloudy and the cross is no longer visible stop the stopwatch and record the time.

* Repeat these steps until a full set of results is finished.

To help me with my investigation I carried out a preliminary experiment the results are as follows:

Concentration (ml)

Time

(minutes/sec)

Sodium thiosulphate

Dilute hydrochloric acid

Water

25

0

0

30:04 sec

20

0

5

43:50 sec

5

0

0

57:04 sec

0

0

5

m:34 sec

5

0

20

4m:21sec

From this preliminary experiment I found out that the higher the volume of water is the longer the reaction takes to happen. This is because it is "diluting" the solution. This helped me as knew that the results of my final experiment would also follow this trend.

When I do the experiment properly I will use more concentrations and I will repeat each concentration so that I can get an accurate average and plot a graph.

For my real experiment I carried out the experiment twice and used more concentrations so that there were more results to work from. The results are as follows:

Concentration

(%)

Volume of sodium thiosulphate (cm3)

Volume of dilute hydrochloric acid (cm3)

Volume of water (cm3)

Rate of

Experiment 1 (sec)

Reaction

Experiment 2 (sec)

Average

seconds

00

25

0

0

35.4

33.8

34.6

90

22.5

0

2.5

40.5

39.0

40.1

80

20

0

5

47.8

47.9

47.9

70

7.5

0

7.5

52.1

52.0

52.0

60

5.0

0

9

64.3

65.6

64.9

50

2.5

0

2.5

79.7

79.8

79.8

40

9

0

5

89.5

87.7

88.6

I have also produced a graph for these results. This on the next page.

The graph for the rate of reaction between sodium thiosulphate and dilute hydrochloric acid shows that:

* The higher the concentration of the solution the faster the rate of reaction

* The lower the concentration of the solution the slower the rate of reaction

The points below show this:

Concentration (%)

Average (sec)

00

34.605

60

04.995

It also shows that it has

* Negative correlation

This correlation shows that the weaker the concentration of the sodium thiosulphate, dilute hydrochloric and water solution the more time it takes for the reaction to take place. As the concentration of the solution decreases the rate of reaction increases. This is because when the solution is more concentrated it has more molecules of the reactants in it and the frequency of successful collisions is greater therefore the rate of reaction is quicker. This is also show in my preliminary experiment.

This shows that my prediction using the collision theory:

"The more molecules there are the frequency of succesful collisions is greater and therefore the reaction rate is speeded up"

Is correct and that it applies to the experiment

My results were accurate but I could have repeated them more often to get more accurate averages.

There were no great anomalous results (fluctuations) in the line of best fit but at 80% there was a slight change in the line. This could be due to human error as I collected enough results for a definite conclusion.

If I had the chance to do the experiment again take more care ion getting the results so that there were not any errors also I could use a

Data logger as this would be computerised and would be able to give more accurate answers, as it is better and no "human errors" could be made