Collision Theory:
The more concentrations, the more collisions. If you double the concentration, you will double the collisions, as there will be more particles in the solution to crash into each other. This proves that concentration speeds up a reaction.
Method:
Measure 10cm of hydrochloric acid
Measure sodium thiosulphate (add water to change concentration)
Put the sodium thiosulphate into a conical flak and add the acid.
Time how long it takes for the cross underneath the flask to disappear.
I will measure the sodium thiosulphate and hydrochloric acid in different measurement cylinders to make sure that it is accurate and they haven’t already been mixed, as this would make the reaction start early. The temperature will be room temperature and as much the same heat as possible, as the hotter it is the faster the reaction will happen, so if there is a great change in temperature the experiment will be affected. I will vary the concentration by adding water to the sodium thiosulphate, and putting less thiosulphate in. I will use distilled water, as this has no minerals in, and normal tap water might, which might influence the speed of the reaction. I will time the rate of reaction by watching to see when the cross has disappeared because it is the most accurate. I will keep the same strength and amount of acid for each experiment.
Equipment: 6 conical flasks
1 beaker
3 measuring syringes (water, acid, sodium thiosulphate)
Stopwatch
A blue cross on white paper.
I predict that the stronger the solution of sodium thiosulphate the longer it will take for the cross to disappear, because there will be more solid sodium, making the solution cloudy.
I will do each experiment three times, for each concentration, for five different concentrations.
Results:
This shows that my predictions are correct and that the reactions happen quicker when the concentration is highest. I had one anomanus result, which was on the first experiment when the concentration was ten. You can see this on the graph.
I could have made my results more accurate by using a burnet to measure the liquids, and keeping the temperature exactly the same – which I could not do because the experiments were done in a classroom on different days. I made sure the conical flasks were the same size. It would have been a good idea to use ICT to plot the graph, if I had used a light sensitive censor, as this would have made it much more accurate. I should also have used a digital clock, as this would have given me a more accurate reading, to the exact time.
I think the experiments worked out well, as I got clear, accurate results. The graphs were quite a smooth curve, and I got the results I had expected. I think that I should have repeated the experiment again to make sure that the results were correct, as this would have made the average more accurate.
