The concentration of the Sodium Thiosulphate is worked out from the table below. The first concentration that I will try is 0.25 mol. To work out the concentration I will use an equation. The equation is
Original Concentration Volume of Na2S2O3 Concentration of Na2S2O3
Final Volume
Prediction
I am going to investigate the concentration of the Sodium Thiosulphate in the reaction. To see how it will affect the reaction. I predict that as the concentration of the Sodium Thiosulphate decreases the time that the reaction takes will also decrease.
Fair Test
A fair test is a test that is as fair as possible. By this I mean only one factor is changed so that the results are consistent and can be compared. To make my experiment a fair test I am going to use the same amount (5cm³) and concentration of Hydrochloric Acid each time but I will change the concentration of the Sodium Thiosulphate but still using the same amount of the liquid (50cm³). This will mean that I can determine what affect the concentration of the Sodium Thiosulphate has on the speed of the reaction. I will do three of each test so that I can take and average which will mean that I can take and average that is going to be closer to the actual result than I single test. It also means that if one of my results is completely wrong because something has gone wrong with the experiment or I have done something wrong I can see that it is wrong and it can be stated. To make sure that this works and is a fair test I need to keep all of the factors that I discussed in the background knowledge the same apart from the one that I am examining. These factors that I have to keep the same are temperature, I will keep this as constant as possible by doing all of the experiments at the same time in the same room. The second factor is a catalyst, I will not add any other chemicals to the experiment other than the concentration of Sodium Thiosulphate and Hydrochloric Acid to keep this factor out of the equation.
Chemicals Given
The chemicals that are given are:
50 cm³ Sodium Thiosulphate at specified concentration
5cm³ Dilute Hydrochloric Acid
Safety
I have one safety consideration that I have to make. This is that I need to wear goggles just in case some of the Hydrochloric Acid or Sodium Thiosulphate splashed and gets into my eyes then I could harm me. This is the only safety precaution that has to be taken.
Equipment list
1 Conical Flask
2 200cm³ Beaker
1 100cm³ Measuring Cylinder
1 10cm³Measuring Cylinder
1 Piece of Paper with a cross on it
1 Stop Watch
The conical flask is for the 2 liquids to be placed in. the conical flask is placed over the cross then the specified concentration of Sodium Thiosulphate is added then the Hydrochloric Acid is added. A conical flask is the best piece of equipment to use because it stops the majority of splashes from coming out of the flask and so reducing the risk of injury.
The beaker is a good choice because it enables me to put the two liquids in before I put them in the conical flask. Thus means that I can have all the equipment and liquids ready to do another experiment as soon as the other one is finished and the flask has been washed other wish the reaction could start prematurely.
The 100cm³ measuring cylinder is the best for the job because a bigger cylinder would have to larger markings to measure the liquid accurately enough and a smaller cylinder would not have enough volume for the whole 50cm³of Sodium Thiosulphate and so you would have to keep on refilling it.
The 10cm³measuring cylinder is the best to measure the Hydrochloric Acid because it has sufficient markings to make it accurate. If a smaller one was used then the cylinder would have to be refilled and with a bigger one it would not have sufficient markings to make it accurate.
The stopwatch is the best piece of equipment to use because a wall clock or watch would not mark the time very accurately and an atomic clock would mark the time to a degree of accuracy that is not needed.
Diagram
This is the diagram of the equipment and how I am going to use it in my experiment.
Method
This is the method for the experiment that I am going to carry out.
- Put a cross on a piece of paper
- Place the piece of paper under a conical flask on a desk
- Pour 50cm³of the specified concentration of Sodium Thiosulphate into the flask
- Add 5 cm³of Hydrochloric Acid
- Time how long it takes for the cross to disappear from sight as soon as the Hydrochloric Acid is added
- Repeat the experiment three time to gain an average
- Try different concentrations of Sodium Thiosulphate
Results Table
These are the results for my experiment. The concentrations are in the order that I put them in the table in the background knowledge section.
Conclusion
From my results you can see that there Is a definite link between the concentration and the rate of the reaction. As the concentration increases so does the rate of the reaction. This is what I predicted in my prediction at the start of the project. The results are what they are because of the concentration theory. As the concentration of the Sodium Thiosulphate increases so does the amount of Sodium Thiosulphate particles in the beaker. The more Sodium Thiosulphate particles in the beaker the more chance they have of hitting the particles of Hydrochloric Acid, because of this the speed of the reaction goes up as the concentration of the Sodium Thiosulphate does.
Evaluation
I would say that my experiment has been very successful. The results that I have obtained have proved the prediction that I made at the beginning and I have been able to say why this has happened.
Looking at my graphs I can say that the results were very accurate. There are no results that are of the lines of best fit and there are no big variations in the results.
I feel that I do have enough evidence from this experiment to support my conclusion and my prediction. I feel that taking 3 results has given me an average that I can rely more apon that one result because one results could be completely wrong and I would have mo evidence to prove that it was not correct.
To improve my experiment I could have use a sophisticated machine that would have measure the amount of precipitate produced and so this would give me a more accurate timing. Apart from this I feel that everything else worked very well.
