Diagram
Method
- A black cross was drawn onto a white piece of paper.
- 10cm² of hydrochloric acid was measured and poured into the conical flask.
- The flask was then place on the piece of paper so that the cross could be seen through the bottom of the flask.
- 50cm² of sodium thiosulphate was added to the acid. No water was added at this point.
- The stopwatch was started immediately.
- The solution was observed from above, and the stop clock was stopped when the black cross was completely obscured by the liquid. The time was recorded.
- The experiment was repeated twice more with the same concentration of “thio” to obtain an average.
- The conical flask was emptied, cleaned and dried.
- The experiment was repeated with a lower concentration of sodium thiosulphate.
- This process was continued with different concentrations of sodium thiosulphate. Each concentration was done three times to get an average.
Fair test
In this experiment we are trying to find the rate of reaction using concentration as a factor, so there is a number of things we need to make sure we do to keep it a fair test.
The hydrochloric acid must be kept at a constant concentration and volume throughout the experiment. The stopwatch must be started at the exact time the sodium thiosulphate (and water) is put into the conical flask. This can easily be done with two people.
Also, the conical flask should be completely clean and free of any water or any other substance before the next experiment is started.
Safety
We must remember that the substances, which we use in this experiment, can be very harmful if used the wrong way.
When we do this experiment, it may be necessary to wear safety goggles, as things are very unpredictable, and even though it is very unlikely that the solution would come out of the conical flask during the experiment, one must still be cautious of spills.
We must make sure that coats and bags are all out of the way while doing the experiment. Ties and hair should be tucked out of the way, so they do not make contact with any of the chemicals. It would also be preferable to wear a scientific apron, however this is not essential.
We should also try our best not to spill any chemicals, and we must not eat or drink in the lab while dealing with these harmful chemicals, as they can get on to our hands.
Prediction
I think that the higher the concentration of sodium thiosulphate, the faster the reaction.
The reason I think that this will happen is because, in a reaction particles collide to give the end results of the reaction. So if there is a higher concentration of particles on a solution, then there will be a high number of collisions. If there are a high number of particles colliding, there is a higher chance of them reacting. This is called the Collision Theory.
Results
Conclusion
In conclusion I have found that my prediction was correct. The rate of reaction was quicker when there was a higher concentration of sodium thiosulphate. This can easily be seen when we look at the results table.
This may have also have been the same if I had used the hydrochloric acid as a variable instead of the sodium thiosulphate. It may have been faster or slower at reacting than the sodium thiosulphate.
Evaluation
I only had one anomalous result, which I will now point out.
This is the only anomalous result that I have recorded. The result may have turned out anomalous because of basic human error, or maybe because we measured the substances wrong. It may have even been because we did not clean the apparatus properly.
Apart from this, the accuracy of my experiment has been more or less accurate. Although there are a number of ways in which we could have made the results more reliable. For instance, we could have used better measuring equipment, because the apparatus we used was mainly basic equipment.
Another thing we could have done to bring more evidence is to have tried to use the hydrochloric acid as the variable substance, and used the sodium thiosulphate as the constant substance. This would have brought more evidence to support the idea that the higher concentration of a substance, the faster it will react.
I think that the evidence, which I have received, is enough to reach a suitable conclusion. My prediction was right. The higher the concentration, the faster the reaction.
