Measure 100ml of water into two large beakers
Prepare all the equipment.
Label the boiling tubes, burettes, and thermometers A, B and C (one for water one for the acid and one for the sodium thiosulphate).
Label the six small beakers with the temperature being used for that beaker.
Step One:
Measure 10ml of the 2M hydrochloric acid into burette one and pour into boiling tube one. Measure 10ml of sodium thiosulphate into burette two and pour into boiling tube two. Place the test tubes in the test tube rack. Place the small beaker on the piece of paper with the cross making sure it covers the cross. (For 200C proceed to Step Four and for 00C proceed to Step Two*)
Step Two:
Light the Bunsen and place it on a blue flame. Now put the two boiling tubes into one of the beakers holding the 100ml of water. Place it all on the gauze and begin heating. Place thermometer one into the hydrochloric acid and thermometer two into the sodium thiosulphate. Use your third thermometer to measure the temp of the water as well.
Allow the temperature to reach 3-5 degrees above the temperature you are going to measure and then turn of the Bunsen.
Step Three:
To get the desired temperature you will have to add some cold water to the hot water. Fill a burette with some water from the unused 100ml beaker. Pour 5ml of the cool water into the beaker and carefully stir. Leave it for 30 seconds. If the temperature is still too high then repeat this process until the temperature is correct to within a degree and then record them.
Step Four:
Remove the hydrochloric acid (using the tongs) and pour it into the small beaker on the paper cross. Immediately remove the sodium thiosulphate and pour it in with the hydrochloric acid turning the cent second clock on at the same time. Place a thermometer into the mixture but don’t stir them.
Watch the reaction from above and turn the clock off when the black cross becomes invisible through the murk. Record the final temperature of the chemicals and the time taken.
Step Two*:
Fill the third large beaker with small chunks of ice. Place the two test tubes into the water and ice. Allow them to cool to 00C or lower if this is possible (unlikely but worth a try).
Once the chemicals are at 00C proceed to step four.
*For 00C only.
Safety:
DO NOT leave the chemicals to boil. It is imperative that they are watched and checked constantly. Wear safety spectacles at all times. Wear a lab coat at all times. Use tongs to remove the chemicals from the hot water. Remember hydrochloric acid is Corrosive and an Irritant and that sodium thiosulphate is also an Irritant. Both chemicals are Harmful as well. In light of this gloves or extreme care should be taken when handling them.
Preliminary Experiment:
My preliminary experiment followed the same method as above except only one temperature was used (200C). Instead of using 10ml each of the chemicals I used 25ml and this is the only significant difference.
The experiment helped me get an idea of what equipment I would be using and how would make my measurements. I also worked out an effective method from the primary one I wrote making a few changes for the different temperatures. The result for my experiment is below.
Experiment one at room temperature/200C:
25ml of each chemical used (total 50ml)
Time taken for X on base of beaker to disappear: 30seconds
Because of this result I decided to lower the amount of chemicals used to 10ml each. I did in this in the hope that it would raise the amount of time taken for the X to become covered by the sulphur as I felt that the reaction was too quick at that temperature so it would be almost instantaneous at a high temperature.
Prediction:
Rate of reaction will increase/speed up when temperature is increased.
Particles react by colliding with each other. For a reaction to take place the particle must collide with enough force to break the existing bonds in the particle. The amount of energy required to break these bonds is called the bond energy and there is different bond energy for every type of bond.
For a particle to collide it must move, for it to move it must have energy. Heating or cooling it can change the amount of energy a particle has. Heating a particle will give it more energy and it will move faster until it denatures or disintegrates. Cooling a particle will remove energy from it and it will move with less speed until it becomes inert (absolute zero).
If a particle moves quickly then there is more chance of a collision occurring successfully. An increase in the amount collisions means that the amount of reactants turned into products per second will also be increased. So the reaction speeds up or the rate of reaction increases.
If a particle moves slowly then there is less chance of a collision occurring successfully because the particles are moving with less force so they may not be able to break the bonds in one collision in which case they will just bounce of each other. This reduced amount of collision success leads to a decrease in the amount of reactants turned into products per second. So the rate of reaction goes down.
Experiment
I carried out my experiment using the above method. All the safety measures were followed and caution was taken when dealing with the chemicals. It took me one and a half to two hours to complete the experiment, including all repeat results.
Results:
The table shows all the data I collected during the experiment in its ‘raw’ form. The starting temperature is the temperature that the reactants were at when they were removed from the water (both were identical). The final temperature is the temperature of the reactants 1-2 minutes after they were removed. The actual heat of reaction lies somewhere between these two values. The last column (time taken) is the time it took for the reaction to finish, in accordance with my set parameters (stated in my introduction).
The separate columns (1st, 2nd, and 3rd) are my results and repeat results. The figures in the first column were always the same so I didn’t place them in separate columns.
Analysis
Average Results:
The above table shows all the results from table one turned into a mean, which is a statistical average. To accomplish this I added the figures in one column and one row together and divided the total by the amount of numbers input. For example:
Final Temperature one=(8+10+9)/3=9
The heat of reaction shows the starting temp added to the final temp and then divided by two. I did this so I could see what the average temperature during the reaction was.
Graphs of Results:
The graph shows the average results. Looking at the graphs I can see a clear relationship between temperature and time taken for the reaction to finish. As I increased the temperature the rate of the reaction also increased. At first the reaction was slow, but with an increase of just 10 degrees the rate of reaction shot up dramatically, as can be seen in the graph. After that the rate of reaction stabilised, gradually getting faster as the temperature was increased.
It is not possible to calculate the rate of the reaction from the evidence I have collected. To do this I would require knowing how much of each product was evolved at each temperature.
Graphs displaying the original data can be found in appendix one.
Conclusion:
The rate of reaction increased with temperature. This is what I predicted would happen.
I think increasing the temperature of the chemicals affected the energy of the chemicals in a positive way (i.e. they gained energy). I feel this way because to do anything requires energy and to do something quickly requires more energy per second than doing something slowly does.
In a liquid energy is expressed by the movement of the particles through the liquid (which is felt as heat). They slip and slide under one another, but they remain held together by weak forces of attraction. As temperature is increased the movement of the particles increases, until a point is reached when the forces of attraction are no longer strong enough to keep the particles together and some escape to become a gas (boiling point).
I stated earlier on in my prediction that for chemicals to react they have to interact with each other by colliding. I also said that increasing temperature would raise the chances of a successful collision (particles which are the same don’t react with other).
I believe this is what occurred in my chemicals. The sodium thiosulphate particles and the hydrochloric acid particles kept on moving faster as the temperature was increased. When they moved faster they covered more distance within the fluid and the more distance they cover the more chances there are of them colliding with each other. I stated that a certain amount of energy is needed for them to react when they collide and if they don’t have enough they just ricochet of each other. If the particles already have that required activation energy then the minute they collide they will react. When the temperature was raised more and more particles had the required energy to react and more and more particles were moving further distances and so a lot of reactions all occurred at once (for the higher temperatures).
Could anything else be responsible for the increase in reaction rate? I would say no because the only significant variable in my experiment was temperature. Can there be another explanation for the increase in reaction rate? Yes. The results I gained could be an anomaly of the two chemicals used.
Evaluation
On the whole the actual experiment was a success as I came to get some decent and reliable results. The results are reliable because they follow a trend and the repeat results are pretty similar to the original ones there. The experiment was a success because nothing went drastically wrong, the safety procedure was all that was needed and the method didn’t require any major improvements whilst I was working. It turned out that my prediction was correct although it is difficult to support the scientific reasons on such a small amount of evidence. The accuracy of my results for the times of the reactions is within 1%. My temperature readings for the starting temperatures are within 1% accuracy, but the accuracy of the final temperatures are within about 10% because there was so little of the fluid in the beakers, which made it difficult for the glass thermometers to absorb heat.
My results don’t follow a clear curve; there is a leap from 4.50C with a time of 95 seconds to 200C with a time of 33 seconds. After this point, however, the results balance out into a steady curve.
There were no anomalous results, except the huge leap in reaction rate that occurred between temperatures 4.5 and 200C. The result is only slightly odd because my repeat results show the same thing occurring. I think the difference was due to a critical point being breached. At around 20 degrees there is enough energy for the reaction to occur quickly, but at 4.5 degrees there is little energy so the reaction takes much longer. I believe that if the temperature were dropped to –200C then the time the reaction would take would be greatly increased.
My current evidence easily supports my conclusion. I can say with certainty that increasing the temperature increases the rate of reaction, at least for hydrochloric acid and sodium thiosulphate.
Improvements:
In hindsight I would change the equipment in several places. The first improvement would be temperature control. The theory for warming the chemicals was good but ineffective for the higher temperatures (refer to my line graph displaying temperatures). I think the heat was lost when I added the chemicals to the beaker. Heating the beaker to a similar temperature to the reactants could prevent this. Using more reactants would also help.
The actual heating of the chemicals could have been easier. Using a beaker and a Bunsen burner is very impractical and hard, especially when you have to hold the thermometer until the temperature is correct. A hot water bath would have been a much easier way of heating the chemicals, plus a lot could have been have been heated all at once thus shortening the time needed. A hot water bath is like a kettle except bigger and you can control the temperature of the water in it.
The accuracy of my instruments was a bit to be desired. The thermometers used are good if you have a lot of liquid, but ineffective when the there is a small amount of liquid. A laser thermometer would have been much preferable and also a lot more reliable and accurate.
Further Work:
To investigate the effect of temperature on reaction rates further other chemicals can be used. Using different substances would tell us if the effect of temperature on my reaction was a strange anomaly of the two reactants or whether it is the norm to see such a trend.
I could also use a larger variety of temperatures, although this would only give me a broader range of results.
ALSO REQUIRED TWO GRAPH ONE FOR EVALUATION AND ONE FOR ANALYSIS. GRAPH OF RESULTS AND GRAPH OF TEMPERATURES.
