The apparatus I will be using are: 10cm measuring cylinder, 25cm measuring cylinder, 100cm measuring cylinder, 250cm conical flask, stop clock, Sodium Thiosulphate, Hydrochloric Acid, Water and a Piece of Paper.
I will measure 40cm of water using the 100cm measuring cylinder and 10cm of sodium thiosulphate using the 10cm measuring cylinder. I will put them into the 250cm conical flask. I will add 5cm hydrochloric acid using the 10cm measuring cylinder to the solution. I will do the same for the 20cm sodium thiosulphate and 30cm water solution, the 30cm sodium thiosulphate and 20cm water solution, the 40cm sodium thiosulphate and 10cm water solution, and the 50cm sodium thiosulphate and 0cm water solution. I will add 5 cm of hydrochloric acid to all of the solutions.
I will record the rate of the reaction in a results table.
The tests will be fair because I will use the same mixture of sodium thiosulphate and hydrochloric acid. The sodium thiosulphate and water will always equal 50cm in volume. I am only going to change the concentration of the solution. After washing the conical flask I will dry it before adding a new solution to it. This will also mean that the cross does not spread and become opaque. I will use the same piece of paper with a cross on it, so the cross is the same colour and shade.
Apparatus
10cm measuring cylinder, 25cm measuring cylinder, 100cm measuring cylinder, 250cm conical flask, stop clock, Sodium Thiosulphate, Hydrochloric Acid, Water and a Piece of Paper.
Method
We measured 40cm of water using the 100cm measuring cylinder and 10cm of sodium thiosulphate using the 10cm measuring cylinder. We put them into the 250cm conical flask. We added 5cm hydrochloric acid using the 10cm measuring cylinder to the solution. We did the same for the 20cm sodium thiosulphate and 30cm water solution, the 30cm sodium thiosulphate and 20cm water solution, the 40cm sodium thiosulphate and 10cm water solution, and the 50cm sodium thiosulphate and 0cm water solution. We added 5 cm of hydrochloric acid to all of the solutions.
We recorded the results below in the table.
Results
Conclusion
After studying my results I have come to the conclusion that as the volume of Sodium Thiosulphate in the solution increases the rate of reaction decreases. This is shown in the results table above and on the graph.
The average rate of reaction decreases as the Volume of Sodium Thiosulphate in the solution increases. When there is 50cm sodium thiosulphate and 0cm water in the solution, the average rate of reaction is 29.6667 seconds. When there is 10cm sodium thiosulphate and 40cm water in the solution, the average rate of reaction is 168.333 seconds. This proves the above statement.
On the graph line A shows that when the concentration is low, the rate of reaction is high – 168.333 seconds.
On the graph line B shows that when the concentration is 20cm Sodium Thiosulphate and 30cm water, the reaction is 79 seconds.
On the graph line C shows that when the concentration = 40cm Sodium Thiosulphate and 10cm water, the rate of reaction is 38 seconds.
I found that when the volume of Sodium Thiosulphate in the solution doubles the rate of reaction does not. In fact it is close to half of the time.
Evaluation
The results indicate that the experiment was a sensible way to test the concentration of Sodium Thiosulphate has an influence in the role of a chemical reaction.
The results obtained in the experiment were consistent and therefore reliable. However, having the Sodium Thiosulphate solution and the Hydrochloric Acid at the same temperature before the start of the experiment. This could have increased the accuracy of the results.
We could have made the measurements of the volume of Sodium Thiosulphate, Water and Hydrochloric Acid more accurate by using Pipettes. We could have also used a light sensor to measure the degree of opaqueness of the cross to a better degree of accuracy.
