Using a catalyst:
This speeds up the reaction and does not be used up.
Surface area:
When reactions are broken into smaller pieces it increases the rate of reaction.
Variables.
There are 4 variables that I need to consider when carrying out this experiment:
Temperature:
The temperature will be kept the same during this experiment. It will remain at room temperature.
Concentration:
We will change the concentration of the sodium thiosulphate. The volume of acid will remain the same.
Catalyst:
We will not be using a catalyst for this experiment.
Surface area:
We are not using solids therefore there is no surface area.
Prediction.
I predict that as we increase the concentration of sodium thiosulphate we will increase the rate of reaction. By increasing the concentration of sodium thiosulphate it increases the number of moving particles, therefore a greater chance of collisions happening with the acid particles.
As I decrease the concentration of sodium thiosulphate, I will decrease the rate of reaction. As there are less particles of sodium thiosulphate, this will result in less collisions taking part.
Observations and Measurements.
I will use 50mls of 5 different concentrations of sodium thiosulphate solution.
These are:
0.050
0.075
0.100
0.125
0.150
For each of the above concentrations I will time how long it takes for a reaction to occur.
Apparatus.
Paper marked with Dropper.
X.
Conical Flask.
Measuring Cylinders. Stop Clock.
Steps to carry out Experiment.
1) Measure out 50mls of sodium thiosulphate solution into a conical flask.
2) Place the flask on top of a piece of paper with an X drawn on it.
3) Add 5mls of hydrochloric acid to the flask and start stop clock immediately.
4) Time until the cross is no longer visible through the solution.
5) Record the results in a table.
6) Repeat steps 1-5 2 more times. Giving 3 times making it a fair test.
7) Repeat steps 1-6 4 times using 0.050, 0.075, 0.100, 0.125, 0.150 of sodium thiosulphate solution.
Tables of Results.
Interpretation.
From my results I seen, when I increase the concentration of sodium thiosulphate it decreases the time taken for a reaction to occur, therefore my prediction was correct. In my predication I said that as I increased the concentration of sodium thiosulphate it would increase the rate of reaction as there would be more particles, therefore more chance of collisions.
I know that my results are accurate as I carried out an experiment for each of the concentrations 3 times and then took the average. I took great care when measuring out the volumes of acid and sodium thiosulphate. I also used the same ‘X’ and ensured that the same person looked through the solution to see when the reaction was over. All of the above ensured a fair test.
If I were to do this experiment again I would uses burrettes for measuring the volume of sodium thiosulphate and the acids. The reason why I would use these is because they are more accurate than measuring cylinders.
In conclusion when the concentration of sodium thiosulphate was 0.050 the time taken for the reaction was 222.7, this is a low concentration and therefore it took a long time for the reaction to occur. When the concentration of sodium thiosulphate was 0.150 the time taken for the reaction was 0.48, this is a high concentration therefore if did not take long for the reaction to occur.