Na2S2O3 (aq) + 2HCl (aq) → 2NaCl (aq) + H2O (l) + S (s) + SO2 (g)
Sodium Thiosulphate + Hydrochloric Acid → Sodium Chloride + Water + Sulphur + Sulphur Oxide.
With the lack of time I was only able to do the experiment once, not three times so I was not able get an average time for each concentrate level. I made sure the volume each time equaled to 30ml. The one thing I kept consistent was 10ml of Hydrochloric acid. I assorted the concentrate of the Sodium Thiosulphate and the Water. This is the results table for the preliminary experiment I done.
Apparatus:
In order to accomplish my investigation effectively, I decided on use these following pieces of equipment.
- Bottle of Hydrochloric acid. (2 Molar)
- Bottle of Sodium Thiosulphate.
- 1 Conical Flask. For the mixing of the solutions.
- 2 Measuring Cylinders. These are to measure the amount of reactants needed. One is to measure the amount of Sodium Thiosulphate and the other is to measure the amount of Hydrochloric acid and Water.
- Digital Stopwatch. For measuring the time of reaction to complete.
- A Piece of Paper. For the cross to be drawn on.
- Safety Goggles. For protection of eye from harmful chemicals.
Fair Test:
I have to assure to keep my experiment as fair as possible, everything but the amount of Sodium Thiosulphate and the quantity of Water will be kept inconsistent but totaling up to stay in the limit of 30ml including 10ml of Hydrochloric acid and not exceeding. The amount of Hydrochloric acid stays unchanged throughout the investigation.
We can tell when the reaction is over, when there is plentiful of Sulphur (solid-powder) to cover a thin pencil cross drawn on a piece of paper. So to keep sure the experiment is of a fair test, the same cross must be used each time.
Another thing that must be taken into account is that the Hydrochloric acid, the Sodium Thiosulphate and Water must be poured into the conical flask at the same instant.
This ensures a fair test; another thing is that the stop-clock is started as soon as the two solutes merge together. (Solutions)
Another aspect which can affect my results is the conical flask. I must wash it out with Water and dry it each time. This is because if there is any solution left in the flask, then it could rework my results and make my investigation unfair. For that reason I must clean out the flask. (A beaker is better. It has a more consistent depth across the whole of its width)
One of the most important factors to judge is the temperature of the investigation experiment. Through qualified information I can tell that the temperature of the reaction will affect the speed of the collisions. So to ensure any unfair activity I must keep the temperature of the entire investigation constant, because otherwise the molecules will gain more energy, unfairly, and will result in additional collisions due to extra speed.
This will tinker with my results and might add anomalous results. In addition I have to ensure that I do not instinctively stir the solution as this will also meddle with my results and surely make the investigation go wrong and unfair.
Safety:
As with all experiments, especially ones which contain harmful chemicals, we have to be extensively cautious. As this particular experiment is not as harmful as others we have to take certain precautions like wearing safety goggles to protect our eyes from any acid splashes and more importantly keeping away from the chemicals not making any contact with the Sodium Thiosulphate as we were told by our teacher that is can cause our skin to go white and peel and also dye our hair blonde.
Method:
To start things of I had to gather all the needed equipment. This includes all the things stated before. Then I had a light pencil cross drawn on a white sheet of paper. I put the conical flask on the cross to see if the cross was clearly visible through the glass, this was just a fair testing measure because the cross would conclude the end of the reaction. After that was done I cautiously added 10ml of Hydrochloric into a measuring cylinder.
I then added 20ml of Sodium Thiosulphate to make the total solution volume of 30ml as said. Because this was the first experiment water was not required. When this was completed I steadily poured the reactants in the two measuring cylinders into the empty conical flask which was placed on top of the penciled cross.
As soon as the two reactants had contact with each other, I instantly started the stop watch. At this point everything was going well, the time was ticking away and the Sulphur was nicely forming making the solution go translucent, but I was waiting for the solution to go completely opaque so the cross was no longer visible, I kept a birds eye view of the solution reacting but making sure that the safety goggles were on at all times, I figured having a view from top would give me a more accurate time as I would have a better view of the cross.
When I saw the cross become totally covered with the solution I instantaneously stopped the stop clock and recorded down the time on my results table.
When that phase was completed and I had the time recorded I removed the contents of the conical flask, washed it and dried it, as this was one of the fair testing steps. After I was ready to restart the process I this time added 17ml of Sodium Thiosulphate, 10ml of Hydrochloric acid but because the total had to add up to 30ml I added 3ml of Water to the Hydrochloric acid this was to lower the concentration of the Sodium Thiosulphate when it was mixed in the conical flask.
The same was repeated as stated before after the two solutions were mixed. I recorded the time after the cross was entirely covered.
This was again repeated several times after, each time adding different amounts of Sodium Thiosulphate and Water but still keeping to the equal 10ml of Hydrochloric acid. You can see the various and random measurements and results further on in the results table.
That was the end of attempt one, but I had planned and went on to do step two and three. I wrote down all the times and went through the fair testing steps accurately. I attempted the experiment three times at different concentrations in order to get accurate and reliable averages, so I could then go on to plot a precise graph and also to see if any anomalies appeared or reoccurred, which are normally caused by not having a fair test or not controlling the variables.
Diagram:
Results Table:
(You must calculate the concentrations of the thiosulphate in mol dm-3)
Results Graph:
Analysis of Graph:
This is the graph I successfully prepared with the results I assembled earlier. My graph should provide you with the pattern of the reaction and help prove my prediction.
From looking at my results and graph I am able to conclude that the more concentrated the Sodium Thiosulphate is the quicker the reaction happens.
Before I did the experiments I made predictions that:
- The cross will be covered by the sulphur powder much more rapidly when a higher concentration of Sodium Thiosulphate is utilized, measured up to a minor concentration of Sodium Thiosulphate.
-
If the concentration of sodium Thiosulphate is doubled, (Explain how you know this) then in general the speed of the reaction will also be doubled. This is because there are twice as many molecules in the same volume; this would be resulting as the molecules being as twice as closer together and the collision frequency being doubled as well. Because of this doubled rate, the time taken for the same amount of sulphur to be produced will be halved.
Looking at my graph these predictions come out to be true, meaning that my prediction was precise and accurate to a high degree.
Examples of this would be that if you look at my graph where the concentration is higher say 20ml the reaction time is 0m.37s.36, where as if you look around where the concentration is lower say 8ml the reaction time is 1m.35s.65. This shows that when the concentration is high the time of reaction is faster rather then when the concentration is low the time is slower.
Another example would be taking a concentration of 10ml where the reaction time is 1m.12, so the expected time at double the concentration, which is half the time as I predicted, is around 0m.36, but the time of reaction is actually 0m.37, this means that the time difference is 1second which is extremely accurate.
(All timings should be in seconds – not minutes and seconds)
Looking at my graph there is an inverse relationship this is because when the concentration of Sodium Thiosulphate increases the time taken for the cross to disappear. This is because when the concentration of the acid increases the rate of reaction decreases. Clearly looking at my graph there are no anomalies. The points easily fit into a curve. (Curve of best fit). This shows that I had considered all factors and conducted a fair experiment. I have got a trustworthy set of results, which can be used for future experiments and research.
Taking all of this into account I have proved my prediction correct, and this can be seen from my graph and results.
About the graph and results:
- Accurate and reliable.
- Repeated and averaged.
- Proved.
- Plotted equally.
- Labeled, units and title.
- Related to prediction.
Testing the graph:
Just as extra measures I decided to take test my graph. I did this by matching up pairs of numbers from a mixture of concentrations of Sodium Thiosulphate. This is to give further proof or my prediction.
Comparing My Results:
This table shows that the relationship is proportional apart from the less concentrated pairs of 5ml-10ml and 6ml-12ml where the results are the slightest bit anomalous, which can easily be caused my minor human errors, but the more concentrated pairs are very close to the expected time varying from 1-3seconds. This would also prove that the curve of best fit is accurate.
Evaluation of investigation:
Overall the investigation went well. I provided the vital processes for the investigation to be successful. I got a well written aim, my prediction went good and turned out to be accurate, I put it in a bit of research about the collision theory, I included a preliminary experiment to show I took time to understand the experiment, the apparatus was written clearly, the fair test was detailed.
The safety was included, the method was descriptively written with step by step information, a diagram was included to show the experiment, a accurate graph was draw due to the reliable results table which was also added, the analysis was detailed and proved the prediction in more than one way and now the evaluation. I have put in as much as I could with good descriptions and detailed writing.
Evaluation on results:
I believe the way I carried out my method was very successful and skilled. I proved my prediction and the investigation was on my side the whole way. I was able to control the factors and was able to carry out a successful experiment and not obtain any anomalies from my final practical results.
My graph shows a perfectly formed curve (curve of best fit) with accurate markings and in order to prove the second part of my prediction the when the concentration increases the taken for the reaction is halved, I drew colour coordinated lines to show the pattern.
I tried my best to keep the experiment as fair as possible but maybe a few uncontrollable factors could have tampered with my results, this could include small drops of water being left at the bottom of the conical flask after I had washed it out, this I could be unaware of and the next time when I added the solution again it could slightly reduce the concentration which slightly then alters with the results. This would be unfair but not knowingly attended. Luckily this did not affect my overall results and did not cause any anomalies.
Improvements:
The experiment was handled fairly but it could have been even fairer. Because the reaction was finished when the cross on the pad disappeared and this is only seen by the naked eye. With the whole class doing this with different eye types, there is no exact fairness in the experiment. Fairness in this issue can be found by using devices such as a light sensor. The light sensor will pass through the flask, of were a reaction is taking place to a receiver. When the light sensor can not reach the receiver, the timing will be stopped automatically. This will bring fairness to experiments to test all similar to rate of reaction. Apart from this minor things like using a different conical flask each time, to assure that no extra Water or left over solution is left at the bottom of the flask, and maybe using devices such as burettes, which wouldn’t make much of a difference.
(Also repeat the experiment several times)
Finalizing this investigation I believe I have accomplished my mission by proving my prediction, collected a reliable set of results and drew up an accurate graph. I have also managed to write a detailed method, analysis and evaluation to this investigation which is probably the most hard and testing parts of this coursework.
