I would expect that the reaction that occurs will be likely exothermic, which means it will give out heat. I predict this because as a precipitate is being formed I think that the amount of energy needed to break the bonds will be less than the energy needed to make the new bonds.
Apparatus
- Sodium thiosulphate solution- will be mixed with the hydrochloric acid
- 2M Hydrochloric acid (dilute)- will be mixed with the sodium thiosulphate and on separate occasions for purposes of the experiment it will be watered down
- Distilled water (because if it were ordinary tap water this may cause some experimental error)- to water the sodium thiosulphate down for experimental purposes
- 250cm³ conical flask- to place the to solutions in for the actual experiment
- 250cm³ beaker to measure the amount of sodium thiosulphate that will be used
- 10cm³ measuring cylinder- to measure the amount of HCl for the experiment
- 50cm³ measuring cylinder- to measure the amount of water to be added to the sodium thiosulphate
- Stopwatch- to time how long it takes for the solution to go cloudy enough so that the X on the card sheet will not be visible to the human eye
- Piece of card paper with a large X on the bottom- to be placed under the bottom of the conical flask for purposes of the experiment
All of the instruments that I will use as displayed above will be used to precise measurements as any of the readings could easily cause some experimental error. For example if I use to much sodium thiosulphate in one test and in the next set of results use too much then this could seriously cause damage to my results and leave me with having to do more experiments.
Plan
I did do a preliminary test as a trial to see if the experiment would turn out as I explained above. The results are as shown:
Fro my preliminary test and results, in the final run of the experiment I did not actually change anything. I kept everything a close as possible to my preliminary test as I think it went vary well. There seemed to be no error and it all ran rather smoothly. I decided there was no real reason to keep the temperature results as this was not part of my experiment and even though may cause some experimental error, I came to the conclusion that the temperature would not change dramatically as it was all done in the same environment and there would be a very slight chance of this happening. In this preliminary test I did not stir the solution and this is one thing I do actually intend to change. This is because the rate of reaction occurs faster due to more successful collision rates and therefore a faster rate of reaction. I do intend to repeat the experiment two more times as this will give sufficient results for my analysis and data.
The experiment should look like the following:
Method
The apparatus will be prepared in a fashion so that the experiment could proceed immediately and so that this would not cause any kind of experimental error due to some kind of miscalculation. A safety mat will be used in case of any spillage of solutions. Safety goggles will also be used during the experiment as a spillage of either the sodium thiosulphate or the HCl could cause sufficient damage to ones eyes. The experiment must not be left unsupervised the whole way through as this could lead to vandalism or risk of fire etc. It is also sensible to ask the supervising teacher to pour out the hydrochloric acid as it is corrosive.
A conical flask will be used to place the solutions into and then commence the experiment. Under the conical flask will be a piece of card with a large X on it. I will then fill the 100cm³ beaker with the hydrochloric acid so that I have sufficient amounts of hydrochloric acid throughout the experiment and the 250cm³ beaker with the sodium thiosulphate again so I will have sufficient amounts during the experiment and use the 50cm³-measuring cylinder for the water. I will also have to label the beakers in case I mix them up.
I will then fill the 10cm³-measuring cylinder with the HCl up to 5cm³ and then measure out 50cm³ of sodium thiosulphate in the 50cm³-measuring cylinder. I will then pour the HCl into the conical flask followed by the sodium thiosulphate. As soon as I have done this, the stopwatch will be started and I will stir the solution.
The stopwatch will soon be stopped after the X on the card underneath the conical flask has disappeared. I will be viewing the X form a birds eye view down the conical flask as the solution starts of clear and then forms a yellow precipitate.
After this part of the experiment is over I will empty the conical flask and thoroughly wash it because it could cause some experimental error later on. Once this is done I will repeat the same idea but instead of having 50cm³ of sodium thiosulphate I will have 40cm³ and 10cm³ of distilled water. This is how I am changing the concentration to find out the rate of reaction. Again the same as above will be repeated where I will add 10cm³ of HCl to the conical flask and the sodium thiosulphate etc.
I will keep doing this until I end up with 10cm³ of HCl and 50cm³ of distilled water where in fact there will be no reaction, as displayed by my results form the preliminary test. Once these set of results are collected and the equipment has been thoroughly washed through, I will repeat the experiment in aid for my evaluation and conclusion.
To make this a fair test I must keep a lot of the variables constant. This means that I must keep the following the same as possible otherwise they could interfere with my set of data:
- Temperature
- Volume of Hydrochloric acid
- Total volume of all the solutions together
The temperature will have to be constant throughout the experiment so that the rate of reaction is not affected. This is because if the temperature rises in any way, the particles will gain more heat energy, which is converted into kinetic energy. This makes the particles move around faster, resulting in more useful collisions, which in turn increases the rate of the reaction and therefore making the experiment unfair. I will not actually be able to keep it constant but I must try my best in keeping everything the same to ensure that a fair test will be made.
I will then have to keep the HCl constant as if I were to change this, it would have a vast effect on the rate of reaction, increasing it if there was too much HCl and decreasing the rate of reaction if too little was added. This would obviously play quite a serious part in the experimental error side and therefore should be measured as accurately as possible.
Also to ensure the test is fair, the variables will have to be done at a fair and precise rate. And what I mean by this is how they should be measured accurately in both tests so that no experimental error could occur because due to these side effects the whole experiment could be affected. The rate of reaction could seriously be affected by what seems such an insignificant piece of data error.
Results
Results of experiment 1
Results of experiment 2
Analysis
I chose to record the sets of data like this as it is set out in a simple way and can easily be evaluated. I chose do six sets or recordings for each experiment for convenience as they numbers were all round and easy to use but partly also because of lack of time to conduct the experiment. We were limited to just only above one hour to conduct our experiment but we were given two separate occasions on what to do so.
It is quite obvious form the tables of results above that as the rate of reaction increased, so did the time for the reaction occur. This shows some kind of link and shows that the sets of results maybe in proportion to one another because as the rate of reaction decreases the time increases and this can also be said with the concentration of the sodium thiosulphate. As the concentration decreases, the rate of reaction decreases but the time increases.
This can then be further linked to the fact that as the distilled water volume increases the rate of reaction decreases and the time increases so they are all in direct proportion. This is all because as the sodium thiosulphate becomes more dilute, there are fewer molecules available for a rate of successful collisions between both the hydrochloric acid and the sodium thiosulphate solution and therefore a decrease in reaction time, proving it longer for the cross on the card disappears. This means that there are now a greater proportion of water molecules that get in the way of the reactant particles. This slows down the time for the reaction to occur as collisions do not occur as often, which determines the speed of the reaction.
Results Table 1 also shows that when there was no sodium thiosulphate present in the solution, therefore only hydrochloric acid and water being present in the conical flask, a reaction did not take place and so the time and there was no record of a time as it kept going on and I would think that it would be an infinite amount of time.
This part of the experiment can be accounted for as a control set of data just to show that the experiment only contained a total of one reactant. The experiment needed two reactants and this is why as the sodium thiosulphate became more and more dilute the reaction time was increasing; it was becoming less of a reactant, where as the hydrochloric acid was kept at a constant rate and therefore always reacted with the sodium thiosulphate.
All of the information that I have just provided can be said exactly the same for the results table two. They both follow a set pattern where as the concentration of the thiosulphate decreased, the rate of reaction decreased and the time for the reaction increased.
From my results I can say that the experiment ran smoothly and all according to my plan and I was not surprised at my results at all. This is due to the fact that I did have a second person accompanying me and this helped a great deal while doing my experiment. This is because in an experiment like this one needs to carry out the actual physical elements of the experiment while the other has to record down results and it is all done in an aid of convenience really.
From the results I have also constructed two graphs, one being for the first set of results and the second graph being for the second set of results. They both show time against concentration and are both done in a way so that there is a line of best fit. Both of the graphs show that the set of results were almost identical as the graphs look almost identical except for on both of the graphs there are two points that do not quite fit maybe due to experimental error but are relatively close and have no real affect on the graphs. These two graphs can also tell me that the experiment went according to plan and that both the sets of data are almost identical as I said and so this means that not much could have gone wrong.
The graphs show that the concentration and rate of reaction are proportional as it is a positive correlation going up in a straight line. This also proves to me that neither of the sets of results differentiated, neither one was faster or slower because on both as the concentration increases the rate of reaction increases i.e. the faster it gets.
Observations
As I was not recording the temperature there is no proof that the reaction was exothermic but all I had to do was feel the bottom of the conical flask where the reaction was taking place and did notice a slight raise in temperature, just by feeling it. This does obviously prove that the reaction was exothermic so my prediction was correct.
Throughout the whole experiment though there was not much else to observe as nothing really that exclusive happened.
Conclusion
I did start this bit of coursework off by predicting that as the concentration of the sodium thiosulphate, so did the rate of reaction (it became faster). This was actually proven by my results as they showed that as the concentration increased so did the rate of reaction therefore proving that they are proportional to one another. This was explained by my attempt in the collision theory of molecules. This is due to the amount of successful collisions that occurred while the higher concentrated solution was being observed and while the lower concentrated experiment was investigated I could come to the conclusion that less collisions were taking place and less of a successful reaction was occurring. The positive correlation of my graphs also shows this, once again as I explained before.
The reason why the results were not perfect in the experiment is because it was not completely fair and it contained many experimental errors, most of which cannot be avoided, such as the change in the room temperature.
Using the collision theory I have come to the conclusion that for a reaction to take place two reactant particles must collide with sufficient energy. In order to do this they must have some activation energy, which is the minimum amount of energy that they must collide with in order for the reaction to occur. The more successful collisions there are the quicker the reaction will be.
Evaluation
I personally think that the experiment was a complete success as nothing major happened and everything went to as according to plan. The results I produced related well to my predictions and conclusions. There was also no safety aspect to be concerned with throughout the whole experiment. So I can say that it is possible for an experiment to commence and run smoothly without any major faults.
The evidence that was recorded, as I have said before, is valid as it shows the rate of reaction is in proportion the concentration and this is what should have happened. It overall was a fair test as there were no variables that were unexpected and as I repeated the experiment twice, both of the sets of results were similar, as they were in the preliminary testing. The evidence and results that were collected obviously proved correct as they supported my conclusions. There were obviously some experimental errors throughout the investigation but these would have been unable to control, such as the temperature of the room, this could increased or decreased at any given time but luckily did not raise any concern during the experiment.
There are also factors such as measuring the three solutions in measuring cylinders and keeping them at an accurate constant. And when I say this I mean that the levels should be accurate every time otherwise this may cause some experimental error and may be a factor of concern when collecting the data. I did though in fact record the solutions as precisely as I could and under the supervision of my partner whilst carrying out the experiment.
There is also the factor of the stopwatch. Even though the recordings were accurate, the stopwatch may not provide a piece of suitable time keeping equipment as it could be slow or the persons reactions who is keeping the time could not be too fast but once again this would raise any major concerns in the investigation.
I have also come up with another way in which I could improve my experiment. My background knowledge on this particular part is not to good but instead of using my own personal eyes so that I can time how long it takes for the cross (as explained before) to disappear underneath the conical flask, I would use a photo electric cell and a light sensor. It is a rather basic process of where I would place the light sensor underneath the conical flask instead of the X and set the photo electric cell above the conical flak. The idea is, as soon as the light sensor is unable to sense anymore light that the cell emits it, hence the solution has reached it’s full potential, we are informed. So I would turn on the cell and stopwatch together and as soon as the light sensor would be unable to fulfil it’s deed and alarm me I would turn the stopwatch off.
This is a much more precise way of getting a reading and would cut any experimental error out when dealing with the time factors. But it is not possible all the time to receive such high tech equipment and the facility was not available for use for the whole class. The diagram below represents this second method.
