If I had an infinite amount of time I would use separate beakers for each experiment but because I am doing each one three times I don’t think the equipment will be available to me so I will just have to be very cautious.
.In my pilot I used higher quantities of acid but I discovered that doing this is a waste of time and wasteful because you can make the concentration differ however much acid and water you choose to vary. I used high amount of acids but then discovered the overall solution had the same concentration so I have been less wasteful. One bad points is that I will have to be very careful with measuring out
My results on the whole are what are incorporated into my prediction. Also in my pilot I decided not to stir the solution because the more you stir the more energy you give the particles and I couldn’t guarantee that I could give the particles the same amount of energy each time and still can’t so I am just going to leave stirring the solution alone
Prediction
I predict the higher the concentration of hydrochloric acid, the quicker the experiment will take to go cloudy with the Sodium thiosulphate, this is due to the collision theory. The collision theory states the more of a certain particle you have in an area the more collision you are going to get with another particle. For example: If you had 4cm ³ of Water, 6cm ³ of Hydrochloric acid and 50cm ³ of Sodium Thiosulphate there is a higher concentration as opposed to 4cm ³ of Hydrochloric acid and 6cm ³ of water because all the water is doing is making sure that the volume remains the same each time therefore there is going to be a higher collision. In a solution where there is a lot of acid in it there is more chance of a Hydrochloric acid particle hitting a Sodium Thiosulphate one.
Unlike an enzyme, Hydrochloric acid once it has reacted, it has been used up where as an enzyme can carry on working after it has broken down a certain particle. From this I expect the reactions to start off fairly fast but slow down towards the end because there will be fewer Sodium Thiosulphate particles and fewer Hydrochloric acid particles and therefore the rate of reaction will slow down. Although you can visibly see this it would be quite difficult to record the rate of reaction accurately within the classroom.
When the solution is going creamy, solid particles of sulphur are forming. Increasing the amount of acid means that the Sodium Thiosulphate will be quicker to turn the solution white, this is because the Sodium Thiosulphate is where the sulphur comes from. I predict if you had the Hydrochloric acid constantly the same and the concentration of Sodium Thiosulphate changing each time that you would produce more solid particles of sulphur because there is more sulphur available in the reaction. It would depend how much Hydrochloric acid you where using.
Word Equation
Sodium Thiosulphate + Hydrochloric acid Sodium Thiosulphate+ Sulphur Dioxide+ Water
Balanced Chemical Equation
Na2S2O3 + 2HCl (aq) 2NaCl (aq) + H2O (l) + S (s) + SO2 (g)
Aq means aqueous solution
L means Liquid
G means gas
S means solid
Another aspect I will predict if an acid is twice as concentrated as another then it will be twice as quick. Going back to the theory of collision, if the acid is more concentrate then there is going to be more acid molecules and therefore there is going to be more frequent and more collisions.
Graphs
Speed of reaction α for time for reaction to finish
This means the speed of reaction is inversely proportional to the time for the reaction to finish. This means as the speed of the reaction increases the time for the reaction to finish goes down. This is called Inversely Proportional
Speed of reaction α 1/Time
This is proportional because as one goes up so does the other one. It will be much easier to plot a graph like this. It will be more accurate to show the rate of reaction over just speed.
Results Table
I have set my results out in three tables. This makes it easy to refer to my results. On each table I have written the Volume of acid in cm³ , Volume of water in cm³, Time taken in seconds. Rate of Reaction (1/Time) rounded to 3 decimal places and percentage decrease from result before which is rounded to 1 decimal place.
Regardless to say each result is the reaction between the concentration of Hydrochloric acid and 50cm³ of Sodium Thiosulphate. The Red result indicates were I restarted the experiment because I did it over 2 lessons.
Results Table 1
Results Table 2
Results Table 3
Average Results Table
Analysis
As my line of best fit on my graph shows three of my results fit through the line of best fit and the other two don’t. This is because I did my experiments over two lessons. When I restarted my experiment in the next lesson ( I have shown this on my results table by making that particular result red) the results changed dramatically to the other two experiments. In the first experiment as I predicted the 8cm³ of Hydrochloric acid against the 2cm³ of Water reacting with the Sodium Thiosulphate had almost double the rate of reaction to the 4cm ³ of Hydrochloric acid against the 6cm³ of Water reacting with the Sodium Thiosulphate, the margin was 1.6%, this is what I expected. The theory is double the concentration, double the speed. Halve the concentration and halve the speed etc.
In the second set of experiments it changed and the percentages went wrong I was expecting the results to be the same as the first one but they weren’t. Instead of a 1.6% margin between the rates of reaction between the two experiments involving 8cm³ and 4cm³ I got a 5.6% margin which means that I did something wrong. The result before the experiment involving 4cm³ of Hydrochloric acid really is the reason that percentage came out unexpectedly.
On the third set of results this point is emphasised. The third experiment seems to change the result so they become less like I expected. The margin is over 20% which is extremely inaccurate. On the third sets of results though I did restart my experiments from the last lesson and the part in which the percentage changes dramatically (third experiment) is the one I restarted on.
My graph does show these anomalies well. As I have been saying the experiments seem to change at the third result and my graph shows this because the first two points (10cm³ Hydrochloric acid: 0cm³ of distilled water and the 8cm³ Hydrochloric acid : 2cm³ of distilled water don’t fit the line but the other three results do. This is because each time the result have been changing at the third result and staying regular for the last two so the line is only going to go through those three. The anomalies are quite a far way off the line of best fit- I think doing the entire set of three experiments over two lessons didn’t help.
Although saying this my graph does show the proportionality well (α 1/Time). This proves that I have actually found the rate of reaction over just speed. If it had been inverse proportionality then it would just be a standard graph which doesn’t show rate of rate of reaction the line would have been like and not like If I had done the concentrations starting with the lowest making my way along it would have looked like the rate of reaction increased.
I can’t really think why it was just the third result which changes the experiment. The third set of experiment really shows that the third result drastically changes the result. There is a various amount of reasons why this may have happened. My results do show the collision theory (that more particles in a certain area the more collision you are going to get but just not very accurately) there were no disaster results so this shows that my results are not totally wrong.
From this I can conclude that my results show that the rate of reaction increases with the increase in concentration. This idea supports my prediction because this is what I said as a general rule. However it only partially supports my idea that double the concentration, double the speed which I thought wouldn’t just partially support my results but fully with a small margin. It also shows the rate of reaction over just speed because you can see the proportionality which I said it would.
Evaluation
The results I have got do not fully support by conclusion. It supports my prediction because the graphs shows the basic idea of the higher the concentration of acid the quicker the reaction but however it doesn’t back fully the idea of double the concentration, double the speed of the reaction. There could be various reasons why this was so but I would have to redo the experiments again but I can’t account for the anomalies so really for accuracy I would have to do the experiments all again.
The main reason for the results being as they are is probably because I had a time limit in which to do the experiment which was two lessons. In this time I would have used two different beakers which would vary the level of cleanliness of the beaker and therefore vary the result.
I can’t think of a reason specifically that the third result came out strange in the last two experiments. It may have been because it was harder to measure out smaller amounts of acid but from that point the results seemed alright. Maybe it is the first two results which are wrong, I don’t know and because I don’t know that means that I can’t say any of my conclusion is correct, so therefore I would have to do my experiments again. These are the ideals I would have
- Sterilized beakers (by heating)- So the beakers are equally clean each time. The reason I couldn’t sterilize them within the classroom is because the option wasn’t available to me. This would means that I wasn’t left with a little bit of the product each time.
OR
2. Different beakers for each experiment- I would prefer to use the above method because you are going to get the same level of cleanliness each time with this you couldn’t guarantee that
3. Each experiment done 5 times instead of three- So the averages would be fairer and the graph would most probably be more accurate
- All the experiment done within the space of one lesson- So that I can work at the same level. I maybe more tired another lesson etc. There maybe other reasons why but I think I would prefer it like this
As I have said my conclusion states -my results don’t fully support my prediction therefore it is not right to draw up a conclusion and because the results in the three tables vary so much , that I would have to do the results at least another 2 or 3 times or ideally 5 times so that I can have fully accurate results, averages and graphs so I would then be able to draw a fully accurate conclusion up.