Equipment I will need
Sodium thiosulphate 0.5g, 0,5g,1.5g,1,5g,2.0g,2.0g,2.5g,2.5g.
50cm³ of distilled water times eight.
50cm³ of HCL times eight.
A thermometer.
A cross.
A stopwatch.
A spatula
A test tube
A mixing bowl.
Factors that could effect rate of reaction
The main things that may affect the rate of reaction are the temperature of the solution, concentration of the solution, the surface area and use of a catalyst. Temperature may affect the rate of reaction because in low temperature particles more around slowly because its cold therefore they are less likely to collide with other particles and react and if they do collide they will collide with less energy and may not react. The hotter the temperature of the solution the quicker it will take to react I predict. Concentration may effect the rate of reaction because in a solution with is lowly concentrated the particles have more room to move around and are less likely to collide with other particles, if the solution is more concentrated there is less room for the particles to move round therefore they will collide more and react more. My prediction is the more thiosulphate added the quicker the cross will disappear because the more thiosulphate in the solution the more concentrated the solution will be and the more concentrated a solution the quicker particles collide and react. Surface area may affect the rate of reaction because large particles have a small surface area in relation to there volume less particles are exposed and available for collisions. This means less collisions and a slower reaction however small particles like the sodium thiosulphate particles have a large surface in relation to their volume more particles are exposed and available for collisions. This means more collisions and a faster reaction. My prediction is that the more thiosulphate added the quicker the rate of reaction because sodium thiosulphate has small particles with a large surface area in relation to their volume so more particles are ready for collisions this means they will react quicker. Using a catalyst in a reaction can also affect the rate of reaction however there is no catalyst used in my experiments so it cannot affect my rate of reaction.
Prediction/Hypotheses
My prediction is that the more thiosulphate added the quicker the rate of reaction because sodium thiosulphate has small particles with a large surface area in relation to their volume so more particles are ready for collisions this means they will react quicker. Also the more thiosulphate added the more concentrated the solution becomes, in a reaction where one or both reactions are in high concentration the particles are crowded close together and will collide with each other more often, resulting in an increased number of successful collisions. Another reason why I predict that the more thiosulphate added the faster the rate of reaction is temperature. The higher the temperature of the reactants the quicker they move around so the more likely they are going to collide with each other. The room tempeture is 22º so I predict that the solution after the thiosulphate added will be around 22º. This is a fairly high temperature so the reactants are going to move around quickly so they are more likely to collide and react. Here is a table of my predicted times after the thiosulphate added
Obtaining Evidence
I have just done the experiment using the method on my planning sheet. Here are my results.
I did not have to repeat any of my measurements
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Looking at my graph there is defiantly a pattern in my results. The graph shows negative correlation in a fairly straight line. This shows that my two variables time and weight of thiosulphate are related. You can tell just by looking at my graph that the more thiosulphate added the less time it took for the cross to disappear. I got these results because of the concentration of the solution, the surface area and temperature of the solution. Temperature affected the results and made the particles react quickly because, in low temperature particles more around slowly because its cold therefore they are less likely to collide with other particles and react and if they do collide they will collide with less energy and may not react. The hotter the temperature of the solution the quicker it will take to react as the tempeture of our solution was 22º which is quite high this is one of the reasons I got the results I got. The most important reason why I got the results I got is the Concentration of my solution. In a solution which has a low concentrated the particles have more room to move around and are less likely to collide with other particles, if the solution is more concentrated there is less room for the particles to move round therefore they will collide more and react more. In the experiment the more thiosulphate we added the more concentrated the solution became, this is why the more thiosulphate we added the quicker it took for the two variables to react and the cross to disappear. Another reason I got these results is because of he surface area of the thiosulphate particles, surface area affected my results because large particles have a small surface area in relation to there volume less particles are exposed and available for collisions. This means less collisions and a slower reaction however small particles like the sodium thiosulphate particles have a large surface in relation to their volume more particles are exposed and available for collisions. This is why there were more collisions and a fast reaction. The reason I got the results I got is because concentration of solution, tempeture of solution and surface area of thiosulphate affected my results. My results do support my prediction because I predicted that concentration of solution, tempeture of solution and surface area of thiosulphate would effect the rate of reaction, I was right my results are what I expected.
Evaluating Evidence
The method I used was very fair I had absolutely no problems with my method as I learnt how to do it without any errors from my preliminary experiment. The quality of my results is good as they all fit my hypothesis pretty well. I measured two results for each measurement to thiosulphate and found an average from looking at the two results I got for each measurement of thiosulphate I can tell that my results are pretty accurate because for all different measurements of thiosulphate the two results were very close to each other. The biggest difference between any two results for each measurement of thiosulphate was 0.79 seconds this was when 0.5g of thiosulphate was being added so the average may not be as accurate as the others however it is still very accurate because 0.79 seconds is a very small difference. I did not get any odd results they all were close to what I predicted. The procedure was very suitable to find out if more of less thiosulphate effects the rate of reaction, the only problem with the procedure was that I was not sure when to stop the clock as the cross never disappeared completely, the solution only got blurry. Maybe next time we could use a indicator to see when it has reacted so it changes to a different colour, then the results would be more accurate. Other than that I think the method we used was the best method to find out what effects rates of reactions. The quality of my results is very good because I learnt from the mistakes in my preliminary experiment. There is defiantly enough evidence in my results and graph to make conclusions, I conclude that the more thiosulphate added the quicker it reacts with the HCL this is because the solution becomes more concentrated, the surface area of he thiosulphate particles is large in relation to the volume and tempeture of solution was fairly high. If I wanted to take this experiment any further I would carry it on this time adding 3.0g,3.5g,4.0g ext. of thiosulphate I would also do it four times ach one to find a more accurate average and change the shape of the contain to see if this effects the rate of reaction. I would also vary the tempeture of the solution to prove that it effects the rate of reaction
