Rates of reaction.

Risk Assessment

I decided to make my experiment safe by wearing goggles at all times and trying not to spill any of the liquid on my clothes and skin.

Step by Step Procedure

. I will get all the equipment out that is on my equipment list.

2. I will fill three beakers one with thiosulphate, one with water and one with hydrochloric acid.

3. I will pour a little of the Hydrochloric acid into the burette and swill it around and then I will pour it away.

4. I will then fill the burette with Hydrochloric acid and a let it out until the meniscus is on the zero line.

5. I will then let out 5 cm of Hydrochloric acid into a conical flask, I will then place the flask on top of a cross on a piece of paper.

6. Then I will measure out 50 cm of Thiosulphate into a measuring cylinder and then pour it into the conical flask with the Hydrochloric acid.

7. As soon as I start to pour the Thiosulphate into the conical flask I will start the timer.

8. I will the watch for the mixture to cloudy, as soon as I can no longer see the cross I will stop the timer.

9. I will then record how long it took for the mixture to go cloudy and for me to no longer see the cross.

0. Then do 40 cm of thiosulphate and 10 cm of water, then 30 cm of thiosulphate and 20 cm of water, then 20 cm of thiosulphate and 30 cm of water and then last of all 10 cm of thiosulphate and 40 cm of water.

1. Repeat each experiment three times and record all the results in a table.

2. Try and get all the readings within 0.1 of each other or as close as you can get.

Scientific Knowledge

The more concentrated the thiosulphate the quicker the reaction between it and the hydrochloric acid. This is because there are more thiosulphate particles to react with the hydrochloric acid particles. The reaction will become slower as the concentration decreases, this is because there are less thiosulphate particles to react with the hydrochloric particles. The solution will become cloudy as the reaction occurs, this is because sulphur is produced.

Key

-Hydrochloric Acid

-Sodium Thiosulphate

Low concentration High concentration

These diagrams show that the more particles of thiosulphate there are, the more chance of them bumping into and reacting with the hydrochloric acid particles.

Equation:

Sodium + Hydrochloric Sulphur + Water + Sodium Chloride

thiosulphate acid

Na2 S2 O7 + HCl S + H2O + NaCl

Results

Preliminary

Concentration of Thiosulphate

20g/l

20g/l

30g/l

30g/l

40g/l

40g/l

Time taken for reaction to occur (sec)

96

97

58

60

34

32

My preliminary runs were to help me to decide the concentration of thiosulphate to use and to give me an idea of how the equipment is set up.

Recording Results

I recorded my results in a table and also in a graph, I will take an average of each set of results to plot the points on my graph.

Amount of thiosulphate (cm³)

Amount of Water (cm³)

- Time taken (secs)

2 - Time taken (secs)

3 - Time taken

(secs)

Average time taken (secs)

50

0

45

46

48

46

40

0

63

59

60

61

30

20

77

80

78

78

20

30

26

27

27

27

0

40

368

369

363

367

Analysis

My experiment showed that the higher the concentration of the thiosulphate the quicker the reaction occurred. This was because there were more thiosulphate particles to react with the hydrochloric acid particles. It also showed that the reaction became slower as the concentration of the thiosulphate decreased, this was because there were less particles of thiosulphate to react with the particles of hydrochloric acid. The solution became cloudy as sulphur was produced and when the cross underneath the conical flask could no longer be seen the time was stopped.

Key

Low Concentration High Concentration

The diagrams show that the more thiosulphate particles, the more likely they are to collide and react with the hydrochloric acid particles.

My prediction was 'The higher the concentration of the thiosulphate the quicker the reaction between it and the hydrochloric acid.' This prediction has been proved correct by my scientific knowledge and my results. My graph shows that I had one odd point when the concentration of sodium thiosulphate was 40 g/l. The reaction occurred quicker than it should have done so maybe the thiosulphate or hydrochloric acid was too warm.

Evaluation

I have completed my experiment fairly by using the same equipment each time, the piece of equipment I used to make the test fair was a burette. I made sure the meniscus was on the line every time I did the experiment which meant that I was using the same volume of hydrochloric acid each time. Also I used the same cross each time so it was fair. I had one odd point on my graph and that was at 40 g/l. I think that the reaction occurred too fast because maybe either solutions temperature was too warm. So next time I will take the temperature of each solution. I also have enough results to support my conclusion and prediction because I took 3 reading of each one.

Faye Cooke 11s