HYPOTHESIS
I predict that as the temperature increases the rate of reaction will also increase. I predict this because of the collision theory, which states that there is more energy with more heat, therefore the particles move and vibrate faster causing there to be more collisions. Also this energy will provide the reactants with enough energy to successfully react by reaching the minimum activation energy. Therefore I predict that the proportion of successful collisions should increase, thus increasing the rate of reaction.
EQUIPMENT
The solutions I will be given are:
300ml of 1.0mol.dmˉ³ sodium thiosulphate
100ml of 1.0mol.dmˉ³ hydrochloric acid
Due to me being given limited supplies of sodium thiosulphate and hydrochloric acid I must select suitable measurements for my experiment. For each experiment I will use 25ml sodium thiosulphate and 5ml hydrochloric acid. This is because it will allow me to gain enough results to draw suitable conclusions and I will also have some spare if I need to redo any experiments or decide to carry out more.
PRELIMINARY WORK
Apparatus and Diagram
2 Measuring cylinders
2 Beakers
Conical flask
Pipette
Paper with cross
300ml of 1.0mol.dmˉ³ sodium thiosulphate
100ml of 1.0mol.dmˉ³ hydrochloric acid
Bunsen burner
Tri-pod
Stopwatch
Thermometer
Method
- Measure 25ml of sodium thiosulphate using the pipette, pour it into beaker
- Measure 5ml of hydrochloric acid using pipette, pour it
- Pour the solutions into conical flask, which is placed on paper with cross
- Time how long it takes for the cross to become no longer visible
- Redo experiment at different temperatures by firstly heating the sodium thiosulphate
Results
HOW TO IMPROVE
After carrying out my preliminary work I have found that my hypothesis was correct. I predicted that as the temperature increases the rate of reaction would also increase. Evidence of this can be seen in my results where the experiment carried out at room temperature took 85 seconds to react, whereas the experiment at 45°C took 24 seconds. Although this trend can be seen there is one major anomaly. This is where the experiment was carried out at 60°C and took just 5 seconds to react, which is even less than when the experiment was carried out at 90°C. The reason for this was due to the conical flask being shaken. Through my background research I know that by shaking or stirring the solution it would given more kinetic energy to the particles, thus increasing the chance of collisions and the molecules colliding with enough energy to reach the activation energy and react, therefore increasing the rate of reaction. I now know that I should not shaken the conical flask and try and keep it as still as possible in my main experiment as it could jeopardize me gaining fair, reliable results. Another fault I found in my preliminary work was that I was using more then 5ml of hydrochloric acid for each temperature. This is because I filled the pipette to 5ml then poured it all out, without realizing that there was more solution in the nozzle. This also would affect my investigation as I would not be using the right measurements, therefore decreasing the reliability and it could cause me to run out of my hydrochloric acid supplies which would not allow me to gain enough results to come to a valid conclusion. Stirred at 5sec
Use pipette correctly – in preliminary work I filled to 5ml but there was more at nozzle – meaning I used too much HCl
MAIN EXPERIMENT
Apparatus and Diagram
2 beakers
Conical flask
Pipette
Paper with cross
300ml of 1.0mol.dmˉ³ sodium thiosulphate
100ml of 1.0mol.dmˉ³ hydrochloric acid
Bunsen burner
Tri-pod
Stopwatch
Thermometer
Variables
In my experiment I must change the temperature to allow me to see how the varying temperature affects the rate of reaction. To do this I will have to time how long it takes until the cross is no longer visible which shows how long it has taken the sodium thiosulphate and hydrochloric acid to react. To allow me to gain fair results, only influenced by temperature I must control several variables. The concentration must be kept constant as it affects the rate (see background material for details). Also I must not move the conical flask, this is because it can also affect the rate of reaction (see background material for details). Another variable I must control is not to use a catalyst. This is due to catalyst speeding up reactions (see background material for details). Also I must control the volume of the sodium thiosulphate and hydrochloric acid solution. This is because by increasing the volume of the solution there would be more particles, therefore increasing the chance of collisions, thus increasing the rate of reaction.
Safety Instructions
Use heatproof mat
Wear safety spectacles
Carry out experiment standing up
Move bags and jackets out of the way
Method
- Measure 25ml of sodium thiosulphate using a pipette.
- Pour sodium thiosulphate from pipette down to the 0ml mark into conical flask (pour the excess into sodium thiosulphate container).
- Measure 5ml of hydrochloric acid using pipette.
- Pour hydrochloric acid from pipette down to the 0ml mark into beaker (pour the excess into hydrochloric acid container).
- Place the conical flask containing sodium thiosulphate on paper with a cross
- Add the hydrochloric acid to the sodium thiosulphate.
- Simultaneously start stopwatch and time how long it takes for the cross to no longer be visible – this will give the reaction time.
- Repeat the experiment at different temperatures. To do this, firstly heat the 25ml of sodium thiosulphate in the conical flask to the required temperature using Bunsen burner. Then add 5ml of hydrochloric acid and time the reaction.
- Once enough readings have been gained, repeat whole experiment again and take averages.
Results
Analysis
Now that I have drawn my graph I can clearly see that as the temperature is increased the reaction time decreases. This can be seen in my graph as the line of best fit has a negative gradient meaning that temperature and reaction time have a negative relationship. The relationship of temperature causing the reaction to speed up can be seen where it takes an average of 40 seconds for the sodium thiosulphate and hydrochloric acid to react at 35°C whereas it takes an average of just 4 seconds to react at 90°C. this has proven my hypothesis correct, where I predicted that as the temperature increases the rate of reaction will also increase. Also from the graph I can gather that temperature is not directly proportional to the reaction time. This is evident as the graph is curved meaning that the reaction time does not change at a constant rate. The graph’s curve becomes less steep as the temperature increases and begins to level out. This shows that as the temperature increases it has less affect on the reaction time. Evidence of this can be seen where an increase of 15°C between 45°C and 60°C causes an average of 8 seconds difference. Whereas an increase of 15°C between 75°C and 90°C causes an average difference of just 2 seconds. In my background research I found that an increase of temperature by 10°C should approximately double the rate of the reaction, my graph proves this correct. This can be seen where it takes an average of 40 seconds for the sodium thiosulphate and hydrochloric acid to react at 35°C and an average of 19 seconds to react at 45°C, which is almost double.
Conclusion
In conclusion I have found that as the temperature is increased the rate of reaction also increases, proving my hypothesis correct. This is due to temperature giving molecules more kinetic energy therefore causing them to move faster and more vigorously. Causing there to be a greater chance of collisions between the sodium thiosulphate and hydrochloric acid molecules, thus increasing the rate of reaction. Also by increasing the temperature it gives the molecules enough energy to break the original bonds so new bonds in the product molecules can be formed. Meaning that there is sufficient energy to reach the activation energy allowing the molecules to react. This causes more of the collisions to be successful, therefore increasing the rate of reaction. Evidence of the increase in rate of reaction can clearly be seen in my results table and graph and is also supported by all by background research.
In my background research I found that an increase of temperature by 10°C should approximately double the rate of the reaction. My experiment proves this, therefore in conclusion I have found that an increase of temperature by 10°C does approximately double the rate of reaction.
Evaluation
I think that the results I have collected have proved reliable enough to draw accurate conclusions from. I have managed to complete my aim of, investigating how temperature affects the rate of reaction between sodium thiosulphate and hydrochloric acid and found the answer that I was expecting. In my hypothesis I predicted that “as the temperature increases the rate of reaction will also increase”. This has clearly been backed up by my results and is also supported by my background research. I feel that I can rely on my results because each set of results was coherent with one another with no anomalies. This can be seen in my graph where there is a clear line of best fit that each reading goes through. Although there are no anomalies in my graph when looking at the results table it is clear that there is a significant difference at room temperature between results 1 and 2. This is due the experiments being carried out at different days therefore meaning that the room temperature was different. If I was to redo the experiment I would carry out the experiment on the same day at a constant room temperature. However, overall I feel my results are reliable and accurate enough and I now believe that by increasing the temperature the rate of reaction will increase. I have been able to come to this valid conclusion as my experiment went sufficiently well. I think this because I used accurate equipment, such as a pipette. The pipette allowed me to collect extremely accurate measurements for my experiment. However, in my preliminary experiment I did not use the pipette correctly therefore causing me to gain unreliable results, which did not follow my instruction. Although this happened it did not affect my main experiment as I used the correct method. Although overall I feel my investigation has gone well, there are faults in my experiment and several ways in which I could improve. One problem with my experiment was temperature. When heating the sodium thiosulphate I was unable to get to the required temperature and keep it constant. This was because by using the Bunsen burner it meant the temperature would continue rising after the required temperature had been met and if the sodium thiosulphate had been heated then allowed to rise to the required temperature it would then fall below it. This was a major problem in my experiment therefore causing it to be unreliable in that way. However, although the temperatures were not accurate, for each result there was a higher temperature and in both sets of results there was a similar temperature used therefore still showing that increasing the temperature causes the rate of reaction to increase. Another way I could improve experiment would be to take more readings and repeat them more than twice. This would make it more accurate and show the trend over more temperatures. Also although I did find that an increase of 10°C does approximately double the reaction time I could only see this between to results. This was due to me increase the temperature every 15°C, if I was to redo the experiment I would increase the temperature by 10°C or if I had a more precise method I would increase the temperature every 5°C.
