Investigating the effect of changing temperature on the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid.

Investigating the effect of changing temperature on the rate of reaction between Sodium Thiosulphate and Hydrochloric Acid. By Toni Bull

Aim:

The aim of this investigation is to find out and observe how temperature affects the rate of reaction. I am going to investigate the changes caused to the solution of hydrochloric acid and sodium thiosulphate when the temperature is changed.

Prior Knowledge/Research:

The rate of reaction is the speed at which a chemical reaction precedes, expressed in terms of the amount of product formed or the amount of unit’s (time taken) for a certain reaction to occur (usually in seconds).

The Rate of Reaction varies greatly. Some chemical reactions, such as explosions, happen very quickly while others like rusting, occur very slowly. The rate of reaction can be affected by a number of factors: temperature, concentration and pressure, adding a catalyst, surface area/particle size and light. The one that I am going to be investigating and explaining about is Temperature.
Changes in temperature change the kinetic energy of the particles and hence the numbers of successful collisions with enough energy to break existing bonds and make new products. The minimum energy needed for a successful collision is called the activation energy.
For a reaction to take place reagent molecules must collide with each other. When they do so, they must possess enough energy to cause or initiate a reaction. The actual energy needed to start a reaction is the activation energy e.g. a splint is needed to start a Bunsen burner in the process of combustion.
So in order to break the energy barrier, there has to be enough activation energy so the reaction will take place. Temperature helps to do this as increasing the temperature of the system increases the range of kinetic energies, increases the average kinetic energy and increases the number of particles with more than the activation energy
Reaction mixtures contain particles that have different amounts of energy. Some particles are of very high energy whilst others are of relatively low or medium energy.

The two theories that affect temperature and the rate of reaction are the kinetic theory and the collision theory. The kinetic theory clearly states that the positioning and movement of particles in a substance increases if the temperature increases. Therefore, increasing the temperature increases the energy between the particles and makes them move around a lot more and collide more often with each particle. If this is done successfully, then the collisions should have no problem passing the requirement stated in the collision theory that are: To react particles must collide with enough energy to break existing bonds and with the correct orientation to bring reactive sites close together.
Bringing the reactive sites closer together means that the likelihood of a reaction occurring is increased so in a final research conclusion, increasing the temperature increases the rate of reaction speed.

Prediction:

As I explained earlier, the rate of a chemical reaction is the speed at which it takes place. Temperature is a major factor in this as increasing or decreasing the temperature changes the movement of particles in a substance therefore changing the rate of reaction. When a reaction mixture is heated up, each particle in it acquires more energy and collides more with other particles.
Thus, from my prior knowledge and research, I can make the prediction that if you increase the temperature of a particular reaction, you increase the speed at which it takes place. This is simply because the particles carry more energy and collide more often, where these collisions contain enough energy to break the energy barrier:

Temperature Raised Particles, when moving faster, collide with greater power.
The reaction therefore becomes faster

Collisions between particles are useless unless they break the energy barrier and this is exactly what increasing the temperature will allow them to do.

Apparatus:

The equipment I need to carry out the work and to obtain my results is:
· Sodium thiosulphate solution
· Hydrochloric acid
· 2 Beakers
· Thermometer
· 10cm /50cm measuring cylinder
· Heat proof mat
· Bunsen burner
· Wire gauze
· Tripod
· Stop clock

Diagram:

Method:

Firstly, I measured 30cm of sodium thiosulphate solution using the beaker, and then 20ml of water using the measuring cylinder. I added these two ...

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Collisions between particles are useless unless they break the energy barrier and this is exactly what increasing the temperature will allow them to do.

Apparatus:

Diagram:

Method:

Firstly, I measured 30cm of sodium thiosulphate solution using the beaker, and then 20ml of water using the measuring cylinder. I added these two together in the beaker. The appropriate temperature was checked using the thermometer. It was at this point where I carried out the various temperatures. At the appropriate temperature, 5cm of hydrochloric acid was measured using the measuring cylinders and then added to the flask containing the sodium thiosulphate. I now placed the flask over the paper, which had a black cross on it that I had drawn earlier.
The stop clock was started immediately to make results more accurate and the time in seconds for the cross to disappear was recorded. I used the Bunsen burner at each temperature with the heatproof mat on it and the wire gauze. I repeated each temperature a total of 2 times to make my results accurate and calculated an average by which I compared each temperature with greater ease. I then worked out the Rate of Reaction for each average.

Preliminary Work:

Preliminary work is the work that is done beforehand for you to know that the values of chemicals and temperatures etc are all within a usable range and are pretty much guaranteed to work. It is a way for the person carrying out the experiment to know that it has been set up correctly for when the actual experiment begins.
For my preliminary work, I did the experiment but did not repeat it four times as I only wanted to see that the values that I was to be using were accurate. This preliminary work helped me to plan my actual investigation better as I learnt from my mistakes. These were things like not starting the stop clock, quick enough, which changed the times of my results.
Therefore, in the actual experiment I am going to be very careful by starting the stop clock at the exact time the hydrochloric acid is added to again ensure fair and precise results.

Safety Precautions:

Throughout this experiment, I made sure that safety was one of my top priorities. I tied my hair up to ensure that it did not get set alight in the Bunsen burner during the experiment. I used a heatproof mat and tripod when using the Bunsen burner and took extreme caution when turning it on and off. I took the same extreme caution when I repeated the results, which I will talk about later on.

Observation:

All rate of reaction experiments have visible results and this experiment is no exception. When I added the hydrochloric acid to the flask I observed immediately at each temperature to see the changes or reactions that were taking place between the particles.
When observing the experiment, the changes I saw take place were the tone of the sodium thiosulphate/hydrochloric acid solution. At the initial temperatures, which were quite low, the solution became very foggy and misty but only after a fairly long time. At the higher temperatures, the solution became foggy very quickly and in both cases, the solution continued to get foggy until it was no longer transparent. I could not see through the solution at all. The colour of the solution went from a clear colourless liquid to a yellowish-green colour and at the higher temperatures, the colour changed almost immediately. I did not see any gas given off or any vigorousness in the actual reaction. The change in colour was smooth and there was no sound made when it happened.

Fair Test:

To make my experiment a fair one, I had to look at a lot of things. Firstly, I looked at the factors that may have affected how well the investigation would work and these were things like using different equipment or doing the actual experiment in different conditions i.e. a colder/hotter environment. To combat this, I made sure that upon repeating the experiment, I used the exact same equipment and done it in the exact same environment to make absolutely sure that the experiment was fair at each temperature.
I think that these were both very important factors because they could affect the results severely and leave me with an anomalous when I should only have correlating results. To ensure fair and accurate results, all of the factors that can affect my results need to be controlled.

Reliable Results:

To make my results reliable, I am going to be doing each temperature 2 times between the ranges of 30˚C to 80˚C (Missing out 70˚C). That’s 5 different results altogether (10 as the experiment is repeated twice) for the temperatures and the average that I will make from the 2 primary results that I record.
I will also make sure that each temperature is calculated to as accurate it can be as recording a result past the required temperature can mean unreliable results which makes the entire investigation void as one result is not calculated correctly.

Results:

I have decided to record my results in a table with a graph that is on a separate piece of graph paper:

Temperature (˚C) Time For Cross To Disappear Average Rate of Reaction
1 2

30 73.84 secs 73.53 secs 73.685 secs 13.57
40 67.50 secs 68.32 secs 67.91 secs 14.73
50 59.27 secs 61.08 secs 60.175 secs 16.62
60 58.15 secs 57.12 secs 57.635 secs 17.35
80 34.17 secs 27.63 secs 30.9 secs 32.36

Analysis Of Results:

From my results, I notice that there is a considerable difference in the time for the cross to disappear from the lower temperatures to the higher temperatures. All of the times are pretty much the same for the two different recordings indicating that the experiment was a pretty successful one. There is no anomalousness and the average temperatures seem to descend, as the temperature gets higher, and the rate of reaction seems to increase. There is a decrease of almost 43 seconds from the starting temperature to the finishing one.
The table clearly shows that the time for the cross to disappear decreases as the temperature increases.

The reaction between Hydrochloric acid and Sodium Thiosulphate:

When dilute hydrochloric acid is added to sodium thiosulphate solution, a fine deposit of sulphur is formed. The sulphur makes the solution cloudy. As more and more sulphur is formed, the solution becomes more and more cloudy. Soon it becomes impossible to see through the solution. The balanced equation for this reaction can be seen below.

Sodium + Hydrochloric Sodium + Water + Sulphur + Sulphur
Thiosulphate Acid Chloride Dioxide

Na2 S2 O3 (aq) + 2HCL(aq) 2NaCL(aq) + H2O (l) + SO2 (g) + S(s)

Conclusion

From my results, I have come to the conclusion that if the temperature of a solution is raised, the time for the reaction to occur is decreased. The cross disappeared more rapidly as the temperature rose and I think this was due to the increase of energy between the particles and an increase in energy between collisions that successfully passed the energy barrier. This released the sulphur quicker and in larger doses, which turned the solution cloudy thus making the cross invisible.
At the lower temperatures, the time for the cross to disappear was less because the particles did not have as much energy as they did at the higher temperatures. At these temperatures the particles are colliding with much more energy and thus the reaction that releases sulphur works and now releases more sulphur at a much quicker rate, increasing the rate at which the cross disappears.

Linking Prediction To Conclusion

My original prediction was that if you increase the temperature of a reaction, you decrease the time it takes to occur. And, from looking back on my results, I can see that this hypothesis was correct as the time for the cross to disappear decreased as the temperature rose. My conclusion matches my prediction very well overall, and my results clearly show this where at 30˚C, the time for the cross to disappear was 73.6 seconds and at 80˚C the time for the cross to disappear was 30.9 - a difference of about 43 seconds. The particles were moving around with more energy; enough to break the energy barrier and for a reaction to occur as the temperature rose.

Evaluation

I think that this experiment has gone very well for me. My results were of a particularly accurate standard as I did each temperature reaction two times and calculated an average from these times. There were no strange results (anomalies) within my results table and I think that this was because of the extreme caution and care that I put into making sure that the experiment was set up correctly with careful measuring of the chemicals.
I think that I could have repeated my results more, however I feel although the experiment was repeated two times, the most accurate results in an experiment can only come from constant repeatability, which I did not display in my experiment. This was as the time allocated did not allow me to do so and I believe as an improvement, if I done the experiment again, I would have to say that, with more time, I would repeat the results further for even more accurate and reliable results.
I believe that I could have improved the method by making it more specific. I stated clearly all the various methods I took in setting the experiment up but I could have been more specific to how all the apparatus was used and perhaps why I used the apparatus I did as well.
I believe that I did get a suitable range of results for this experiment. I recorded results from temperatures that ranged from 30˚C to 80˚C and I think that this is a very good range to see how temperature affects the rate of reaction. However, I feel that this also reduces the chance of knowing if anything changes if the temperature reaches a certain point. Perhaps doing the temperature even higher would enhance my results but this is also quite dangerous so I cannot really say that I could have improved the range of my results, and there would have also been problems with keeping the liquid hot enough, long enough to complete the experiment.
Some other areas in the experiment that I feel I could have improved on were factors like controlling the stopwatch and measuring the amount of sodium thiosulphate and hydrochloric acid. There is lots of room for human error here. However the inaccuracies due to them were negligible because I paid close attention to these during the experiment.
Overall, this investigation has been a very successful one. I feel my results and analysis have been as accurate and reliable as they could have been under the time allocated. However I feel with extra time, I could have repeated the experiment and made it even more accurate and adapted it to try other variables i.e. concentration or adding a catalyst. These are the ways that I could expand on the original question.