View from above the beaker:
The cross disappears when enough Sulphur forms to blot it out.
What factors would effect the rate?
- Concentration increase of Acid or Sodium thiosulphate.
- Temperature increase of Acid.
- Catalyst.
Which factor will I investigate?
I will investigate increase of Sodium thiosulphate concentration.
What do I predict?
I predict that the reaction goes faster, when the concentration of the reactant is increased. The more successful collisions there are, the faster the reaction.
In dilute acid, there are not so many acid Here the acid is more concentrated.
particles. This means there is not much chance There are more acid particles in it.
of an acid particle hitting a Iron atom. There is now more chance of a successful collision occurring
As time goes on…………………
At the start, there are plenty of Iron atoms and After a time, there are fewer Iron acid particles. But they get used up during atoms, and the acid is less successful collisions. Concentrated. So the reaction slows down.
Blank table
This is what the table will look like that we will record our results in.
Fair testing.
To insure the test is fair the overall volume of sodium thiosulphate must be kept the same. The temperature must also be kept the same and the volume of acid remains constant.
Safety.
We must wear goggles at all times incase of an accident e.g. glass breaking or acid getting into your eyes.
Equipment.
1x goggles
1x conical flask
3x measuring cylinder
3x beakers
1x stop watch
Plan.
Start
- Set up equipment.
- Measure enough Hydrochloric acid, water and Sodium thiosulphate into 3 beakers.
- Mark a cross on a piece of filter paper, place under conical flask.
- Measure 50cm of Sodium thiosulphate into the conical flask. Measure 20cm of hydrochloric acid, and no water. Add hydrochloric acid to conical flask. Start stop watch immediately. Stop the stopwatch when cross disappears. Record time in table. Repeat once more for accuracy. Record in table. Get rid of mixture safety.
- Measure 40cm of Sodium thiosulphate into the conical flask. Measure 20cm of hydrochloric acid, and 10cm water. Add water and hydrochloric acid to conical flask. Start stop watch immediately. Stop the stopwatch when cross disappears. Record time in table. Repeat once more for accuracy. Record in table. Get rid of mixture safety.
- Measure 30cm of Sodium thiosulphate into the conical flask. Measure 20cm of hydrochloric acid, and 20cm water. Add water and hydrochloric acid to conical flask. Start stop watch immediately. Stop the stopwatch when cross disappears. Record time in table. Repeat once more for accuracy. Record in table. Get rid of mixture safety.
- Measure 20cm of Sodium thiosulphate into the conical flask. Measure 20cm of hydrochloric acid, and 30cmwater. Add hydrochloric acid to conical flask. Start stop watch immediately. Stop the stopwatch when cross disappears. Record time in table. Repeat once more for accuracy. Record in table. Get rid of mixture safety.
- Measure 10cm of Sodium thiosulphate into the conical flask. Measure 20cm of hydrochloric acid, and 40cm water. Add water and hydrochloric acid to conical flask. Start stop watch immediately. Stop the stopwatch when cross disappears. Record time in table. Repeat once more for accuracy. Record in table. Get rid of mixture safety.
- Clean all equipment and place in correct cupboard or draw.
Finish
Table 1
Before experiment
After the experiment the table was recorded and it looked like this:
Table 2
After experiment
Results will be illustrated as a graph, which should look like this:
To fully understand rates we understand that rate is directly proportional to 1/t. If we draw a graft of 1/time against concentration we should get a straight-line graft through the origin, showing us that rate is directly proportional to the concentration. We should be therefore be able to show that the concentration doubles.
Conclusion and Interruption
The reaction went faster, as the concentration of sodium thiosulphate is increased. This is shown in table 2, where the reaction went faster as the volume of sodium thiosulphate was increased. This is also shown in both graphs.
There seams to be no strange results. But if there was it could be for a number of reasons including:
- Solution came from different flasks.
- Measurements were not accurate.
- Conical flask was not cleaned after each test.
Improvements.
- Use solution from same flask.
- Clean conical flask after each use.
- Repeat experiment for accurate results.
- Made better control of temperature.
Evaluation
As my prediction was right, this is what happened in my experiment. My graphs also show that my prediction was correct.
In the experiment the diluted Here the acid is more concentrated. acid had not so many particles, there was more acid particles in it
as I said there is not much chance therefore there was a greater of an acid particle hitting an iron chance of a successful collision.
atom
AS TIME WENT ON………
At the start there were plenty After a time, there are of iron atoms and acid particles, fewer iron atoms, and the
but they got used up during acid is less concentrated,
successful collisions so the reaction slowed
down
