This is because the higher the concentration of sodium thiosulphate the more frequent the collisions will be between the sodium thiosulfate and hydrochloric acid particles. Therefore bonds will break quicker and new bonds will be formed which will make new products quicker. Therefore the rate of reaction will increase. I have found out that there is a pattern, as the concentration increases the rate of reaction also increases. This is because a higher concentration of reactants leads to more effective collisions per unit time, which leads to an increasing reaction rate.

Because a more dilute sample of hydrochloric acid there will be less molecules of actual hydrochloric acid, and more water particles. This means that there is less chance of a hydrochloric acid molecule colliding with a molecule of sodium thiosulphate, and so there are less successful collisions in any given amount of time, so the rate of reaction is slower. The results show that as the concentration of sodium thiosulphate increases the time taken decreases, therefore the rate of reaction increases. This is because if there is less water, the solution is more concentrated.

The more concentrated the solution, the quicker the precipitate will form, (faster rate of reaction), and vice versa. If you double the concentration then you will double the frequency of collisions between hydrochloric acid and sodium thiosulfate particles thus doubling the rate of reaction. This may create a positive correlation on my graph between the rate of reaction and the concentration. This will probably create a smooth curve as I plot the readings from the outcome of my experiment. WORK OUT GRADIENT FOR GRAPH Evaluation:

TALK ABOUT COLOURIMETER How good are your results then? error sources?can we improve the existing method? are there other experimental methods? Do your results seem consistent and accurate – always refer directly to the graph or graphs in your analysis … do any of the sets of results not fit in with the others? , do most/all sets of results fit a pattern? , are there any particular points that don’t fit the pattern? (anomalies), can some results be ignored in drawing your conclusion(s)? if so, which results and why? QUOTE DIRECTLY – WITH REFERENCE TO YOUR GRAPH(s)

Discuss possible sources of error which might lead to where these or any other factor OK?in other words how suitable was the method overall? Do think the results are reliable bearing in mind any anomalies? For the hydrochloric acid – sodium thiosulphate reaction think about the precipitate, observing it etc. What further experiments, using the same method or another method, My results are not as accurate as it could be because I have not repeated it each concentration 3 times but only done it once. Looking at my results table, I have found an anomalous result because as I increase the concentration of the water and the sodium thiosulphate the reaction time also increases, as you go down the table.

But on my third test it suddenly drops to 07. 25 seconds. This may have happened due to slow reaction-time when timing. As I draw my graph I expect to clearly see an outlier because of this odd result. I feel the method that was used to collect the results was very successful because there were no errors in my results. My results were tested again in a repeat experiment, the results of which were almost identical to the first results, only fluctuating within one second. The most difficult part of the method was measuring accurately the amount of sodium thiosulphate, HCL and deionised water in the measuring cylinders.

I found this difficult because the cylinders were not as accurate as I would have liked and relied on my eye to judge when the liquid lever was equal with the intervals on the side of the cylinder. The method used produced results accurate enough to show to show that as the concentration of sodium thiosulphate increases, so does the rate of reaction, but the method was not perfect as it was subject to human error. The results were not as accurate as they possibly could be because of various constrictions in the lab in which the experiment was carried out.

The most accurate measuring cylinders used to measure the amounts of acid and sodium thiosulphate and rely on the human eye to judge when the amount is accurate. This could have caused slight errors in the amounts of solution or acid being used. A way to correct this could be to use a more accurate piece of measuring equipment such as a pipette. Another possible problem could come from judging when the black X has disappeared from view. The human eye is not accurate enough to judge the instant the black X disappears consistently.

This could be solved by using something more accurate to measure how much precipitate has formed, and when the amount formed has blocked the X on the paper underneath the flask.

Bibliography 1. http://www. purchon. com/chemistry/rates. htm 2. http://www. chem4kids. com/files/react_rates. html 3. http://www. richardanderson. me. uk/keystage4/GCSEChemistry/m3ratesofreaction. php 4. Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Patterns of Behaviour section.