The cross, which is under the breaker, is very important; this piece of apparatus tells us when the experiment is over as then it is obscured from our view by the sulphur that is produced.
In order to do a fair test, everything has to be the same, even if one of the mixtures is stirred or shake as this gives the particles more kinetic energy which makes them collide faster and therefore have a higher rate of successful collisions.
In order for the chemical to react, the particles have to collide with each other, and heat gives them activation energy to get them moving around, so if the we have done this experiment in 0 oC, no matter in what concentrations, nothing would happen due to the particles not having enough energy.
Apparatus:
- Beaker x 3
- 25 cm3 Burette
- 20 cm3 Burette
- 10 cm3 Burette
- 5 cm3 Burette
- Conical flask
- Graduating pipette x 2
- Safety goggles
- Cross on the paper
- Stop clock
- Laboratory coat
Preliminary results
To help me plan my experiment, I decided to do some experiments before to get an idea of what was going to occur when carrying out my real experiments.
Diagram of the whole set up of apparatus
Method:
To try and research the effect of concentration on the reaction, which is to find out how long it takes to cover the whole cross underneath, I am going to measure the time it takes with a stop clock.
Those are the concentration that I am going to change the concentration with adding water in:
- 25 cm3 (100%) of Sodium thiosulphate / 0 cm3 (0%) of water
- 20 cm3 (80%) of Sodium thiosulphate / 5 cm3 (20%) of water
- 15 cm3 (60%) of Sodium thiosulphate / 10 cm3 (40%) of water
- 10 cm3 (40%) of Sodium thiosulphate / 15 cm3 (60%) of water
- 5 cm3 (20%) of Sodium thiosulphate / 20 cm3 (80%) of water
I need a big cross, which is ready, and printed on a piece of a paper. What I do next is put the cross underneath the breaker where we mix the chemical in order to do this experiment. The mixture of sodium thiosulphate is always adds up to 25cm3. One of the chemicals can put in the breaker first, then we can put the other chemical afterwards, as soon as we put those chemicals together, then we can start the experiment, and at the same time we have to press the start button on the stop clock, and also we can stop the stop clock when the cross is completely gone. The time it takes will then be record on to a table, and then what I am going to do is do the different concentration for three times and then work out the average, so that the result will be more reliable.
To insure to do fair tests, there are some important point that we have to look at: Chemical has to be the same amount, the breaker has to be the same size, and also we have to wash the breaker probably, so the no chemical is going to be left over to effect the experiment.
Although I am going to change the concentration, but I am keeping the volume of both chemicals the same at 25cm3, I am going to use 25 cm3 of those two chemicals because I think it is easier to work out the way of changing the concentration and work out the percentages, and also that’s what I used in other experiments, so I think it’s better to keep the volume the same.
Preliminary work:
To help me plan my experiment, I decided to do some experiments before to get an idea of what was going to occur when carrying out my real experiments. Here is a table of the results I obtained in my preliminary work.
Table of results
Results in bold I believe stand as anomalous results.
After each experiment, the apparatus were washed out straight away so that the chemicals in the conical flask don’t make the glass go misty, therefore this would affect the reaction time and make the results wrong as the experiment would take less time as the glass already is quite misty.
Analysis
When looking at the table of results and graph 1, it shows that as the concentration of the sodium thiosulphate increases along with the rate of reaction. But however the time taken for the cross to be unseen from the view where I look from the top of the breaker through the mixture of the chemical decreases. We can tell by the graphs by the points plotted. The line goes up when lowering the concentration as the reaction takes less time due to the kinetic theory and the number of particles present in the mixture and reaction.
On graph 2, which shows the rate of reaction. As the concentration of sodium thiosulphate increases, the rate of reaction increases. Again, we can tell that by the line that joins up with the dots, it is almost a straight line, apart from one point went out of the line.
When analysising the graphs, we see that there is only one anomalous result. An anomalous result is distinguished by a difference of 10% from the average of the other two results.
How we expect them to be arranged.
Whatever concentration we use, the result we get would be the result we get for time sing the result for concentration (1). That’s why we do preliminary work, so we can roughly work out what we get in between. But I didn’t do one for this one because I didn’t have time.
Conclusion:
I found out during the experiment, as we increase the concentration of sodium thiosulphate, the rate of reaction would also increase, it is caused to be like this because whatever the concentration is, there would still be the same amount of chemical in it. If the concentration is low, there would have more water particles in there, even thought the amount of chemical is the same but it actually has less sodium thiosulphate particles in.
With fewer particles in, there will be a less chance for the sodium thiosulphate particles to hit the particles of Hydrochloric acid, so therefore the reaction would take place slower. At opposite way, if increase the concentration of sodium thiosulphate, more particles involves, and more chance for the sodium thiosulphate to hit the hydrochloric acid, and reaction take place faster.
Does the conclusion support the prediction?
I think the conclusion support the prediction pretty much, I predicted that as we increase the concentration of sodium thiosulphate solution, it would increase the rate of reaction. I’ve found out that is true. Also I stated that as the reaction take place faster, the time taken to finish the experiment would be shorter, which I found is right after doing the experiment.
Evaluation:
When looking at the table of results, they are almost perfect but there was one anomalous result at the lowest concentration of sodium thiosulphate. When looking at the results table we can see one anomalous result that comes up in the lowest concentration, which was 5cm³. This may have been caused due to a number of factors, such as wrong measurement of concentrations, time, room temperature fluctuation and the washing out of the conical flask in between the different experiments. When first did this experiment, the result went really bad, first I tried to change the concentration of the hydrochloric acid, and the result didn’t come out very well, I did two concentration which is 100% and 80 %, and there were only 0.73(s) difference between those two, so I decided to change the concentration of sodium thiosulphate, and it went rather improved, but it had not gone as accurate as I thought.
There were several things that I could do to make the result a bit more accurate. For example, it could be better to measure the chemicals in a more accurate apparatus. I used a measuring cinder instead of a Burette or a graduate pipette, that’s a very important thing. Second thing is I should have washed and dry the breaker very properly, if the breaker was not dry and cleaned up probably, the concentration can be change by that, it might not be a lot, but it can effect the experiment and the results, and we can get some unreliable results.
So after tried using more accurate ways and more accurate apparatus, the result went a lot better. As we look at graph 1, there were only one point which is out of line, but I was a lot please than before, because it went more accurate, perhaps its just an mistake, if we are professional scientist then it would be very accurate, but at least I tried my best.
An very important, as we do this experiment, because we didn’t do all those tests in that day, and we were doing the temperature on room temperature, and weather can change everyday, and weather can effect the temperature, it’s either speed up or slow down the reaction, because heat gives the particles more kinetic energy, and opposite way, it gives less energy when temperature is low. So therefore doing the investigation on changing the temperature will be more of a fair test.
Also, using the burette is not easy, its very hard to get everything to be the same amount, it can’t be hundred percent accurate. And I tried my best to get it to be a fair test.
Further work in this investigation would be to take a sample after 2 minutes from the mixture using a graduated pipette to put the sample into a cuvette. Then you would place the cuvette in a colorimeter and set it to see what percentage of light came out the other end through the mixture. You would do this for each experiment so you could get another table of results to plot some graphs to analyse and draw conclusions.
After talking through the problems and the accuracy of things, if we were given more time, we could do more concentrations of sodium thiosulphate, or perhaps do the temperature, also shine a light through the mixture of chemicals, because that way we can see the cross more clearly, and through the liquid, and then it would extend the experiment.
