No. of particles
with given KE
Hotter substance
Higher temperature
Activation energy
Energy Min K.E for reaction
No of molecules with K.E > The minimum energy needed to react is directly proportional to the shaded area
By looking at the graph one can say that by looking at the shape of the curve the area surely must increase with increased temperature.
The Preliminary Experiment
The aim of the preliminary experiment was to find out suitable concentrations of thiosulphate one should put in to the reaction. I did not want to end up doing the experiment without knowing how long it will take and which concentrations would be suitable.
Method
- Apparatus: Conical flask, burette, stopwatch, a cross on a piece of paper, a thermometer and safety glasses.
- Safety procedures: One must wear safety glasses at all times because there are dangerous chemicals in the experiment. One should also stand up when doing the experiment so if the flask falls off the bench you do not get hurt.
- Firstly I chose three concentration levels for the experiment. These are shown in the table below.
- I designed the concentrations to be like this so the total concentration between water and thiosulphate would be 50cm3. This is a good round number. Water is only present to balance the numbers.
- I measured each liquid in a burette. A burette is a very accurate means of measurement and is the best way of measuring liquids.
A Burette
- Once all the liquids have been measured separately we place them in a conical flask, which is placed on top of a cross.
- After every part of the experiment one should wash the conical flasks out because if one doesn’t then there will be bits of the solution still on the sides of the conical flask, which could easily influence the experiment.
- I place a thermometer in the conical flask so I can make sure that the reaction is remaining constant. Remember we are not changing the temperature so it is imperative that we monitor the temperature so nothing goes wrong.
- Once everything is ready we start clock. Here are our results.
- The amount of time taken for this experiment is just about right. Not too long and not too short. In the main experiment I will use these volumes and more volumes within these brackets.
- My conclusion to this experiment is that if I half the volume of thiosulphate in the reaction the reaction will take roughly doubly as long. The more thiosulphate that is in the reaction the faster the reaction will be.
Although I will not be able to carry out an experiment to investigate into how temperature effects the rate of reaction I will still talk about it. Temperature is the most influential factor in rate of reaction.
The main experiment
The aim of this experiment is to find out how the effect of concentration influences the rate of reaction of thiosulphate.
Method
- Apparatus: Conical flask, burette, stopwatch, a cross on a piece of paper, a thermometer and safety glasses.
- Safety procedures: One must wear safety glasses at all times because there are dangerous chemicals in the experiment. One should also stand up when doing the experiment so if the flask falls off the bench one doesn’t get hurt.
- I chose six combinations of thiosulphate and water volumes to study the progress concentration has on rate of reaction. In the table below one can see the volumes I have chosen.
- There is only one use of water in this experiment and that is that it will balance out the total volume in the conical flask.
- After every part of the experiment one should wash the conical flasks out because if one doesn’t then there will be bits of the solution still on the sides of the conical flask, which could easily influence the experiment.
- I will measure each liquid in a burette. A burette is the most accurate way of measuring liquids. It is even better than a measuring cylinder. This is because a burette is much thinner so each point on the burette is much more accurate.
- Once each and every one of the liquids has been measured we must place them in a conical flask. Under the conical flask there should be a cross.
- One must place a thermometer in the flask so one can make sure that the temperature is kept constant.
- Once everything is ready start the clock.
- Once the solution has turned opaque you can start again.
- Note that for the main experiment one should have at least five different results (in my case six) and repeat them twice.
The second variable, which will remain constant during the experiment, is the effect of temperature. I am not going to carry out this experiment but I will explain an experiment to test the effect of temperature on the rate of reaction of thiosulphate. The aim of this experiment is to find how big an effect temperature has on the rate of reaction of thiosulphate with dilute hydrochloric acid.
Method
- Apparatus: Thermometer, waterproof pen, conical flask, burette, safety glasses, clamp and a stopwatch.
- One must always wear safety glasses, as there are dangerous chemicals in the experiment we are doing.
- I believe that a concentration of thiosulphate, which is sensible to use for this experiment, is 25cm3. If I chose 50cm3 as a volume to use then I would find that there would be not much change in the times. As a volume 25cm3 is not too big and not too small.
- We measured each liquid in a burette. A burette is the most accurate form of measurement that I can use.
- After every part of the experiment one should wash the conical flasks out because if one doesn’t then there will be bits of the solution still on the sides of the conical flask, which could easily influence the experiment. One could even put a brush in the flask and try to dry it out.
- Before doing anything I will mark the bottom of the conical flask with a waterproof pen. This is because once I can’t see the mark anymore then the reaction has finished and the solution is opaque.
- When the liquids have been measured one should find the conical flask with the mark on it and clamp it with a clamp to the water bath.
Water Bath
Conical Flask
- Pour all the liquids into the conical flask and make sure that the HCL goes in last as the HCL starts the reaction.
- Just in case one should place a thermometer into the water bath just to monitor the temperature.
- Finally one may start the clock and note down the results in a neat table.
- Note that one must do this experiment at various temperatures. So for example for this experiment I am going to use the temperatures 10 degrees, 20 degrees, room temperature, 30 degrees, and 40 degrees. I will repeat the experiment twice more.
Unfortunately I did not have time to do this experiment so I have no results but I predict that if I increase the temperature by 10 degrees as I had explained earlier the rate of reaction will double. So if I decrease the temperature by 10 degrees then the rate of reaction will halve.
Obtaining the Evidence
Analysis
Conclusion: From my graph I can see that the more concentrated the sodium thiosulphate is the higher the rate of reaction will be.
By looking at my graph I can see a definite trend. This trend is that as the concentration of sodium thiosulphate increases, the rate of reaction increases too. Therefore when I doubled the concentration, double the precipitate was formed in a given time. Thus, the cross was obscured in half the amount of time.
One must note that these results are an average of all three attempts at each concentration. If one looks at the results tables one will find that all the results are very similar or even exactly the same as the average result. Because this is the case I haven’t plotted three different graphs. The theories surrounding this experiment i.e. the effect of concentration and temperature will be found in the planning.
If one looks back at my predictions one can see that they are right: the rate did double as the concentration doubled. This is because the higher the concentration the more particles were present in the given volume. This would mean that there would be a greater amount of collisions in the given volume. Hence the reaction would take a lesser amount of time.
Firstly my graph supports my prediction that if I increase the concentration the rate of reaction will also increase. This is because the line of best fit is straight and has a positive gradient. Also my graph supports the idea that if I double the concentration the rate of reaction doubles. This is because the positive line goes through the point (0, 0). This suggests that the relationship between concentration of sodium thiosulphate and the rate of reaction is directly proportional.
Evaluation
I have looked back at each of my predictions, my results and my graph and I can safely say that my experiment worked. All the results were similar. Other colleagues of mine have got similar results; my graph boosts my evidence to suggest that if I double the concentration the rate of reaction will double also. Similarly if I increase the concentration the rate of reaction will increase also. The method that I used seemed to work. From my graph I can say that there were no anomalous results. By looking at my evidence there are no major floors in the experiment but this doesn’t mean that there weren’t any minor hiccups because no experiment is perfect.
There is no doubt about it I have made some minor errors in this experiment. Firstly no matter how good my eyesight is there would have undoubtedly been a human error in the way I judged when the reaction was over. One cannot trust the naked eye to judge a whole experiment. I would improve the way we judge whether the reaction is over by using a light source. This light source would shine through the conical flask to a light detector. When the light detector cannot detect any light the reaction is over. I believe this is a better way of doing the experiment, as the light detector is more trust worthy than the naked eye. This diagram of the light source will show you how this new method works.
Light Source
Reaction Light Detector
Mixture
The amount of light passing through the flask decreases as the sulphur precipitate builds up. This can be recorded on a simple light detector or even a data logging equipment. The rate curve is measured as follows.
Intensity
Time
Another error is that although one may wash out the conical flask after every part of the experiment excess water might still be left in the flask. This could change the total volume and enhance the experiment. The solution for this problem is that yes one should wash each conical flask out but also one should stick a brush into the conical flask so the flask is clean and dry.
In the experiment we controlled the temperature using a thermometer however this may not be accurate enough way of controlling the temperature. To improve on this error one could place the conical flasks in a water bath and clamp them to it. Then mark the temperature at room temperature. This is a more trustworthy way as the room temperature could easily shift. While doing the experiment the window was open, which was not too, far away from me so this could affect the temperature levels. Luckily the water baths are no where near the window so there is no hope of a shift of temperature levels.
As I have said earlier there were no anomalous results in my experiment. As there were none the evidence in my investigation is almost certain to justify the conclusion.
If we want to go further into our investigation we can look into how temperature effects the rate of reaction. Method
- Apparatus: Thermometer, waterproof pen, conical flask, burette, safety glasses, clamp and a stopwatch.
- One must always wear safety glasses, as there are dangerous chemicals in the experiment we are doing.
- I believe that a concentration of thiosulphate, which is sensible to use for this experiment, is 25cm3. If I chose 50cm3 as a volume to use then I would find that there would be not much change in the times. As a volume 25cm3 is not too big and not too small.
- We measured each liquid in a burette. A burette is the most accurate form of measurement that I can use.
- After every part of the experiment one should wash the conical flasks out because if one doesn’t then there will be bits of the solution still on the sides of the conical flask, which could easily influence the experiment. One could even put a brush in the flask and try to dry it out.
- Before doing anything I will mark the bottom of the conical flask with a waterproof pen. This is because once I can’t see the mark anymore then the reaction has finished and the solution is opaque.
- When the liquids have been measured one should find the conical flask with the mark on it and clamp it with a clamp to the water bath.
Water Bath
Conical Flask
- Pour all the liquids into the conical flask and make sure that the HCL goes in last as the HCL starts the reaction.
- Just in case one should place a thermometer into the water bath just to monitor the temperature.
- Finally one may start the clock and note down the results in a neat table.
- Note that one must do this experiment at various temperatures. So for example for this experiment I am going to use the temperatures 10 degrees, 20 degrees, room temperature, 30 degrees, and 40 degrees. I will repeat the experiment twice more.