To Investigate the Effect of Changing the Concentration On the Rate of Reaction In Two Experiments

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Simon Shepherd 13th February

Chemistry Rates of Reaction Practical Coursework

Planning Experiment 1

Aim: to investigate the effect of changing the concentration on the rate of reaction in two experiments - sodium thiosulphate and hydrochloric acid, and magnesium and hydrochloric acid.

Method: a cross will be drawn on a piece of filter paper and placed underneath a conical flask. The substances required - sodium thiosulphate, hydrochloric acid and water will be measured out. The water will be used to dilute and therefore vary the concentration of the sodium thiosulphate. 5ml will always be measured out of hydrochloric acid as a constant with a 10ml measuring cylinder. The water and sodium thiosulphate will always total to 50ml and will be measured with a measuring cylinder of the same value. The sodium thiosulphate solution will be added first, and as soon as the hydrochloric acid is poured into the conical flask the timer will be started. The reaction will then take place, and the solution will turn cloudy over a period of time. When the cross on the filter paper has been completely obscured, the timer will be stopped and the time taken recorded. The rate can then be calculated by dividing 1 by this value.

Diagram:

Safety: one of the reactants, hydrochloric acid is corrosive so skin contact with it will be avoided. Sulphur dioxide, a toxic gas, will be produced during this reaction. Therefore, I will not stand over the apparatus to avoid inhaling it. Also, the reactants will be disposed of in a fume cupboard when the experiment has finished.

List of Apparatus:

* 250ml conical flask, chosen because the thin neck limits sulphur dioxide emissions, and the broad base makes it easier to see the cross on the filter paper without standing directly over the experimental.

* Digital stop clock accurate to half a second as it is easier to read than an analog clock and no more accuracy than this is required.

* 10ml measuring cylinder to measure the 5ml of hydrochloric acid to the maximum amount of accuracy possible.

* 50ml measuring cylinders to measure out the water and sodium thiosulphate. This is the most accurate value that could be used as the measuring cylinder has to measure volumes from 5ml to 50ml.

* Filter paper for a cross to be drawn on.

Preliminary Results: the following preliminary results were obtained.

Volume of

Volume

Volume

Na2S2O3

of Water

of HCl

Time

Cm3

cm3

cm3

s

50

0

5

22.0

40

0

5

33.0

30

20

5

47.5
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20

30

5

75.5

This range of readings clearly gives enough variation to make it easy to determine what type of relationship occurs between concentration and rate on my graph.

Number of Readings: 8 readings will be taken spread evenly over the range above to allow for the correct type of graph to be determined. Also, each reading will be taken twice to detect any errors, if they occur. If two readings of the same value of concentration differ greatly, the readings will be repeated so no anomalous results occur to make my ...

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