In basic terms, at a cold temperature the reaction will take more time to happen. This is because the particles of sodium thiosulphate and hydrochloric acid will not be moving around so quickly, meaning they are less likely to collide, therefore the reaction will require more time in order to occur. Chemical reactions require a collision at a certain velocity, and if this velocity is not reached then the reaction will simply not happen.
As the temperature increases, the rate of reaction will be lower. This is because with more heat, the particles have more energy, meaning they move around more. Collisions will be more likely to happen at a higher speed.
- Set up apparatus (see diagram)
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Mix 30cm2 of water and 30cm2 sodium thiosulphate in a measuring cylinder.
- Place in hot water bath until temperature reaches required amount
- Pour into a conical flask
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Measure out 30cm2 of Hydrochloric acid
- Pour into conical flask and time reaction
- When the reactants are mixed, you should fund that the solution becomes cloudy due to the fact that sulphur is precipitated. As this gets thicker, the cross underneath the conical flask slowly disappears.
I will ensure a fair test by keeping the concentration levels of sodium thiosulphate, water, and hydrochloric acid the same throughout the experiment. I also washed out each piece of equipment we used after each experiment. By doing this, it should have prevented any potential contamination from the previous experiment. Finally, we conducted three trials in order to make sure that there were know anomalous or out of place results.
I will make the results precise and reliable by once again conducting threes trials to make sure that there were know anomalous recordings and washing out the equipment we used after each experiment to prevent any contamination passed on from the experiment before.
Obtaining Results
Trial 1
Trial 2
Trial 3
Average
I have controlled other variables to make it a fair test by keeping concentration levels the same throughout the experiment, but also by using the same equipment, in this case the conical flasks to keep surface consistent.
Conclusion
After analysing my results, I have come to the conclusion that the temperature does affect rate of reaction, and therefore form the theory that the higher the temperature the lower the rate of reaction. I can see this from results table and graphs because the lowest temperature has the highest reaction time. For example, 21°C took 58 seconds whilst the higher temperature, 61°C, has the quickest reaction time of 11 seconds. Like I mentioned, my graph also helped me to see this. At the lower temperatures the line of best fit goes very high, and at the higher temperatures the line of best fit is very low.
This is because with more heat, the particles of sodium thiosulphate and hydrochloric acid have more energy. This causes them to move around more. Chemical reactions require collisions, and if two sets of particles are moving around quickly there will naturally be more collisions. However, the collisions require the particles to hit each other at a certain velocity, and if this velocity if not reached then the reaction will just not happen. So, at the higher temperatures, more of the particles were travelling at a high enough speed to collide and react. At the lower temperatures it was more difficult for the particles to collide. Only some were able to reach the required speed and react.
The particle theory says that for a chemical reaction to occur, there must be a collision at a certain velocity and at a certain angle. Also, the factors that affect the rate of a reaction are the surface area of the pieces of solid, the concentration levels, the presence of catalysts and lastly, temperature. In this experiment we were concentrating on temperature, and we were able to draw the conclusion that temperature does, in fact, affect the rate of a reaction, by using the results and evidence to suggest that when the temperature is higher the reaction takes less time.
At 21°C the reaction took a long time to occur. This was because there was not very much heat. Heat provides energy to the particles of reactants, and if there is not very much heat, the particles do not have very much energy and because they do not have much energy they will not move around much, and will therefore not collide as often. Chemical reactions require a certain speed collision to react, and at this temperature very few of the particles collided, because of not moving around more due to lack of heat that in turn supplies the energy.
Between 31°C and 61°C the rate of reaction drops very dramatically. I can tell this from my graph, as the line of best fit goes down very steeply. This is because the heat has given the particles some, but not all, energy, and they were able to move around a lot more than previously. The particles then collided more and reacted together.
To summarise what I noticed, firstly the reaction goes faster at higher temperatures. And secondly, the reaction rate is about twice as fast as it rises by about 10°C. This is the case when you look at my results. For instance, the cross becomes out of sight in 58 at 21°C, yet in around half the time, 26.5, at 31°C.
I also found in this experiment that;
The rate of reaction = Amount of sulphur precipitated
Time for cross to disappear
However, I also realised that the cross disappears at the same thickness of precipitate every time, therefore, the amount of sulphur precipitated is the same at every temperature. So, after taking this into account;
The rate of reaction 1
Time taken for cross to disappear
This equation is shown in my graph (rate of reaction against temperature). From this graph, you can clearly see that the rate of reaction increases as the temperature rises.
I feel it is safe to say that my results support my prediction well. They prove the fact that temperature does affect the rate of reaction. I also have the particle theory to support my prediction and conclusion. The only side of my prediction I didn’t truly understand was that I wasn’t aware that there would be a dramatic decrease in reaction rate on the lower temperatures. Considering I was without any evidence from an experiment, I am pleased to say that I think I made a good scientific prediction.
Evaluation
Also, as the temperature got higher, the results were closer together, and as we had to round the time in seconds (our stopwatch didn’t have a mille second dial) to an integer they became less accurate. If we rounded the time more accurately (e.g. to 2 decimal places), our results would become more reliable. Another reason for the higher temperatures being very close together is that the water in the solutions was starting to change state as it neared its boiling point of 100C. It also didn’t help that other pupils felt the need to play around with the temperature of the water bath.
We increased the concentration of the Sodium Thiosulphate and the Hydrochloric Acid so that our results would be slightly more accurate, because sodium thiosulphate and hydrochloric acid have higher boiling points and so the higher temperatures would not be so close. We would then be able to tell more easily how temperature affects reaction rate.
We made our results more accurate by taking multiple readings and then an average time from these. We felt the need to do this because you can’t really judge from 1 lot of results, because it’s possible that something went wrong, or you timed incorrectly. I mean, it isn’t easy to see time the exact moment that the cross disappears.
Concerning the amount of time taken for the cross to disappear, we could use a different method of working out how long the reaction took to occur. For example, we could shine a torch through the conical flask, and as soon as the light cannot shine through any more, we would stop the stopwatch.
We found that there was one anomalous result. It is shown on my graph. The reason for this could be that it was timed wrong because it was quite a low temperature, it took a reasonable amount of time for the cross to disappear. This would have made it difficult to judge the exact moment that it disappeared, as it would have been gradually changing. I realise that we could have measured wrong in this case. To be fair, it was very difficult to start the stopwatch exactly at the same the sodium thiosulphate and hydrochloric acid were put together. I mean, they would have already started reacting before the stopwatch was started.
Another possibility for the anomaly is that there was some other factor affecting the reaction rate. The four factors that affect the rate of a reaction are the surface area of the solid pieces, the concentration of levels, the presence of catalysts and temperature. In our experiment the dependant variable was temperature, and if the concentration of one of the solutions had changed for some reason i.e. some water may have been splashed onto it then the experiment would not be a fair test as a result.
To extend the investigation into how temperature affects the rate of reaction, you could perform the experiment in a vacuum, as then there would be no other factors that can affect our results, other than temperature, which is all we to investigate in the first place. I would also like to have the opportunity to user greater temperatures and see how the rate of reaction was affected once the temperature reached its boiling points. I would have done this if I had more time.