Experiment to show how concentration affects the rate of reaction

Method 

1. Firstly take 50cm3 of Thio (sodium sulphate), using a different cylinder measure 5cm3 of hydrochloric acid.

2. On a piece of paper draw a cross, place a conical flask over the paper and add the Thio and acid.
3. Immediately start timing and swirl 3 times.
4. Stop timing as soon as the cross under the flask isn’t visible.
5. Repeat steps 1-4 twice using the SAME measurements. Record your results.
6. Now do the experiment 3 times using 40cm3 of Thio, 10cm3 of water and 5cm3 of acid. Record your results.
7. Then do the experiment another 3 times using 30cm3 of Thio, 20cm3 of water and 5cm3 of acid.
8. Repeat the experiment another 3 times using 20cm3 of Thio, 30cm of water and 5cm3 of acid. Record your results.
9. Lastly do the experiment 3 times using 10cm3 of Thio, 40cm3 of water and 5cm3 of acid. Record the results.
10. Place all results in a table and calculate the average time for each experiment.

NB red writing indicates when a new batch of Thio (sodium sulphate) was used

Analysis and Conclusions

The more concentrate the solution the quicker the ‘ X ‘ disappeared i.e. The reaction went quicker when the solution had less water in it (more concentrated)

Graph 1 shows that as the concentration increases the time decreases. Graph 2 shows that the concentration is directly proportional to the rates. As the concentration increases so do the rates.

The more concentrate a solution the quicker it will react because it has many more particles than a diluted solution of the same solutes. There is a bigger chance of a collision when the solution is more concentrate because there are more particles, when the particles collide the reaction will take place. As more water is added to the Thio solution the reactions take longer to take place, backing up my prediction – the more concentrate the quicker the reaction takes place.  

Evaluation

I carried out the experiment to the best of my ability. I used suitable equipment and apparatus thus gaining accurate results. All three times I got for each experiment were very close, although the equipment may not have been accurate. It was very hard to decide when the cross had disappeared. Luckily I was using a digital stopwatch which was extremely accurate. The graduations on the cylinders were very faint, therefor hard to read accurately. To get rid of this problem we would have to use new equipment which would be far too expensive. For four of the experiments I used a new batch of Thio which could have made a difference, fortunately not in my case. My graphs show that I didn’t obtain any anomalous results, so my results must have been accurate. As with any experiments you are going to encounter difficulties, although there were a few I think it was a good procedure and as long as you carry it out slowly and cautiously you will obtain accurate results. I think my results draw a firm conclusion that concentration does affect the rates of reaction, i.e. the more concentrate a solution the faster the rate of reaction.

       Dilute Solution                               Concentrate Solution

The diagrams above show that in a more concentrate solution there are more particles present. This means that the reaction will take place quicker because the sodium Thiosulphate is able to collide into more particles which makes the reaction happen faster.