Prediction (1) – I predict that when the concentration is high then there will be a faster reaction.
Scientific theory – If there is a high concentration there will be more particles for the thiosulphate to collide with. This means that there will be more frequent collisions.
Prediction (2) – If we double the concentration from 0.2 molar to 0.4 molar or 0.4 to o.8 molar, then the rate of reaction should half.
Scientific theory – This is because there will be double the amount of thiosulphate for the acid particles to collide with.
Low concentration High concentration
0.2 molar 0.4 molar
Apparatus
300cm conical flask
25cm measuring cylinder
100cm beaker
Stop clock
Sheet of paper with cross on it
1 H Hydrochloric acid
Sodium thiosulphate
Goggles
Method
*Put on goggles as a safety precaution*
- Measure 50cm of sodium thiosulphate, pour it into the conical flask.
- Start the stop clock and add 5cm of hydrochloric acid at the same time.
- Shake the flask very gently and then place it over the cross on the paper.
- Keep looking through the top of the flask, when you cannot see the cross stop the stop clock.
- Repeat with different concentrations of thiosulphate.
Diagram
Results table
Conclusion
I found out that the concentration did affect the rate of reaction. When there was a high concentration there was a faster rate of reaction, when there was a low concentration of sodium thiosulpahte, the rate of reaction was slower. This was because in the high concentration there was more Sodium thiosulphate particles to collide with the acid particles, therefore there were more frequent collisions. With the low concentration there were less sodium thiosulphate particles to collide with the acid particles, therefore there were more frequent collisions.
0.2 molar 0.8 molar
There was a pattern in my results. I found out that when the concentration doubled the rate of reaction almost halfed, however, this only happened when I changed the concentration from 0.2 M to 0.4 M. This is because the number of thiosulphate particles has doubled therefore there are more particles and more frequent collisions.
The first prediction that I made was correct, I predicted that the higher the concentration, the faster the rate of reaction. This shows in my results table and my graph. In the graph, the steeper the slope is on the line the faster the rate of reaction is.
The second prediction wasn’t very accurate, looking back at my results I found out that the as the concentration went from 0.2 molar to 0.4 molar the time didn’t half. The average time at 0.2 molar was 231.3 seconds and at 0.4 molar the time was 90 seconds, these times don’t nearly double. The times for 0.4 to 0.8 molars are closer, being 38.7 seconds and 90 seconds.
Evaluation
The most inaccurate parts of my experiment were the timing and the measuring of the acid, water and sodium thiosulphate. I wasn’t watching the experiment as closely as I could have been and I could have stopped the stop clock more accurately if I had been paying more attention. The measuring was done quite quickly with not much accuracy. This would have probably affected my results and if I did the experiment a second time, I would try to make the experiment more accurate. This could have been helped if we had more time to carry out the experiment.
I could improve my experiment in many different ways. I could use a wider range of concentrations for example 0.2m, 0.3m, 0.4m, 0.5m and so forth up to 3.0m. This would give me more results to compare. I could use different intervals between the concentrations for example 0.2, 0.4 and 0.6 I could use 0.2, 0.3, 0.4 this would give me a better set of results. If I had done the experiment more times to find a more accurate average, this would give me more accurate results. I could also try using concentrations that double such as 0.2 M, 0.4 M, 0.8 M to see if I could perhaps prove my second prediction.
I think that although my results weren’t perfectly accurate they were good enough to make a reliable conclusion. The results did agree with my predictions but I could have done the experiment more accurately. If I did the experiment again I would definitely use a wider range of concentrations in order to gain a more accurate set of results.
