The chemical equation for investigating the rates of reaction by experimenting with increasing and decreasing the concentrate of Sodium Thiosulphate and Hydrochloric Acid is as follows:
Na2S2O3 (aq) + 2HCl (aq) —> 2NaCl (aq) + S (s) + SO2 (g) + H20 (l)
Plan:
The apparatus needed is as follows:
-
Sodium Thiosulphate Solution (Na2S2O3)
- Hydrochloric Acid (2HCl)
- Paper marked with a cross
- Beaker
- Conical Flask
- Stopwatch
- Measuring cylinder (x2)
Method:
- Measure 10ml of Sodium Thiosulphate Solution and add 5cm³ of Hydrochloric Acid.
- Start the stopwatch and record the results when you can no longer see the cross on the paper.
- When repeating this experiment, take away 1ml of Sodium Thiosulphate Solution. Each time this is carried out, add an extra 1ml of water/
- At the bottom of the conical flask, place a piece of paper marked with a cross. When the solution has turned sufficiently cloudy so that the cross can no longer be seen, the stopwatch will be stopped and the time will be recorded.
- When both reactants are added together in a conical flask, place a beaker over the top. This prevents any gasses escaping that are produced.
Diagram:
Prediction:
The rate of reaction is the rate of loss of a reactant or the rate of formation of a product during a chemical reaction. It is measured by dividing 1 by the time taken for the reaction to take place. There are five factors which affect the rate of a reaction, according to the collision theory of reacting particles: temperature, concentration (of solution), pressure (in gases), surface are (of solid reactants), and catalysts. I have chosen to investigate the effect concentration has on a reaction.
I predict that the more dilute the Sodium Thiosulphate Solution becomes, the longer it will take to react and for the solution to become cloudy so the cross is no longer visible. And I predict that the results will show a pattern and the time taken will increase as the solution becomes more dilute. I think this because if you refer back to the collision theory you will see it says that before colliding molecules react, they must have an energy equal to or greater than the activation energy for the reaction. This means that the graph of results drawn up will have a positive correlation and will probably be curved as the increase in rate of reaction will not be exactly the same as the concentration is increased.
Results:
When the two reactants were added together, they produced an unpleasant smell. The colour of the product changed from clear to a cloudy yellow. The results were close to my prediction and I predicted well. I know this because if you look at the graph, you can see that it is a curved graph, and it has a positive correlation. Each time this experiment is repeated there is a pattern occurring. The less Sodium Thiosulphate added and the more water added, the more dilute the end solution became. This resulted in a longer time to completely turn cloudy. Sodium Chloride, Sulphur, Sulphur dioxide and water were all produced.
Table of results:
As you can see above in the table of the results you can see that the less Sodium Thiosulphate added and the more water added, the more dilute the end solution became. This resulted in a longer time to completely turn cloudy and the cross on the paper was no longer visible. I have decided to make a table to show the rate of a reaction. See below:
Conclusion:
My conclusion is that every time the experiment is carried out there is a pattern occurring. The more dilute the solution is, the longer it takes to react. If you look at the graph you can see the rate of reaction peaks when the solution is less dilute.
Evaluation:
My evidence could be relied upon to be correct because the solutions were accurately measured in measuring cylinders and the results were very reliable as the stop clock measured the time in hundredths of a second, which is extremely reliable evidence. I think I do have enough evidence to draw up a conclusion as I have done, because I recorded 3 sets of results along with an average result and a table for the rate of reaction, which uses the collision theory to calculate the number of collisions per second. I think the experiment worked well and the results backed up my prediction – the fact that the more dilute the solution, the longer it took to react. I think that to improve this experiment I should have used a light and sensor with a computer in place of the piece of paper with a cross on it. I would do this by placing a light under the flask, which would probably be held on a tripod, and a censor above the conical flask, which would be connected to the computer. This would recognize the light through the censor, and when the solution became cloudy, the light would be blocked, therefore causing the censor to detect this, and the computer will record the time taken. This would be extremely accurate. Another thing that I could use to improve this experiment is to use a burette to get a more accurate reading of the solutions, which could have varied the results. It would make measuring the solutions a lot more accurate and therefore the results may have varied. All in all I think this was a good experiment and the best that could have been done with the time and resources available. The results supported my predictions and they seem to be fairly reliable results.
