The preliminary experiment really helped me in knowing what to expect when I did the real experiment. Having the knowledge gained from doing a preliminary experiment was a great aid.
Planning
In my experiment testing the rate of the reaction when Sodium Thiosulphate is added to dilute hydrochloric acid I plan to, investigate the concentration of the sodium thiosulphate. I shall start be measuring out, using a burette, ten cm cubed of hydrochloric acid, and fifty cm cubed of sodium thiosulphate. They will be added together and timed, using a stopwatch, until all visibility has gone. A cross will be drawn on white paper and placed under the conical flask during the experiment. When the cross is no longer visible the stopwatch will be stopped and the time recorded. The concentrations tested will vary from pure sodium thiosulphate to five cm cubed of sodium thiosulphate diluted with forty-five cm cubed of distilled water. The total amount of the sodium thiosulphate and water solutions will always be fifty cm cubed. I have decided to change the concentration of the sodium thiosulphate rather than the hydrochloric acid because in my preliminary the results of rates of the reactions were too fast. With the concentration of sodium thiosulphate being changed the time taken should be slower and easier to record. The other factors affecting rate of reaction will be kept the same. The evidence I collect from doing this experiment will be put in a table and graphed to show the positive relation between concentrated and the time taken for the reaction. This experiment is based upon the collision theory, which states that for a reaction to occur, molecules must collide not only with sufficient energy but also with the proper orientation. Having looked at this theory I predict that the lower the concentration of the sodium thiosulphate solution will affect the rate of reaction. I also predict that lower the concentration the longer the change in time taken.
Apparatus=
- Three burettes and burette stands,
- One conical flask,
- Three beakers,
- A thermometer,
- Paper with a cross on it,
- A large supply of sodium thiosulphate,
- Hydrochloric acid and distilled water.
The table I collect my evidence in will look like this:
The Collision Theory
The collision theory is an idea that explains the rates of the reaction. It says that for the two substances to react together the molecules must collide with each other and that the collision must have enough energy.
The rate of a reaction depends on two factors.
1) The number of collision per unit time between the reacting species.
2) The fraction of these collisions that is successful in producing a mew molecule.
The rate of reaction must depend on how many successful collisions there are in a given unit of time.
Observing
The evidence that I collected during my experiment was done using a simple and safe procedure. This meant that I was able to conduct my work without fear of danger. Here is the evidence I collected:
As shown in the table the evidence I collected does support my predictions, and the general collision theory. However, my results do show one anomaly. This is in the first result I took. This is most likely due to incorrect measuring, a human error.
Analyzing
My evidence shows very clearly that the rate of reaction is positively affected by the concentration of the substances. My graphs clearly show that the rate of reaction is affected by the concentration of the substances involved in the reaction. On the graph there is a clear curve, excluding one result, an anomaly, which I account for due to human error in measuring. This shows that the lower the concentration the loner it takes, and the lower the concentration goes the longer amount of time it takes (shown by the presence of the a curve on the graph). On the graphs you can clearly my inaccuracies particularly at the beginning resulting in the graphs not appears as symmetrical as they should.
Evaluating
In this experiment there is large evidence to support the statement that my results aren’t accurate due to either human failure or the speed of the equipment available. If better, faster equipment had been available for the experiment my results would be more reliable. Improvements could include using a computer to time and say when the solution has gone cloudy, leaving less room for human error.
