For this experiment we are looking at the effect of concentration on the rate of reaction between Sodium Thiosulphate and hydrochloric acid, to do this we will be diluting the Sodium Thiosulphate using distilled water.
Diagram
Method:
First place the conical flask on the tile marked with a ‘X’.
Then using one of the measuring cylinders to measure 40cm3 of Sodium Thiosulphate, then get another measuring cylinder and measure out 10cm3 of Hydrochloric acid, after this put the 10cm3 hydrochloric acid in the conical flask, now be careful (you may want to use another person) as after you have put the 10cm3 hydrochloric acid in the conical flask put all the Sodium Thiosulphate in the conical flask and with the other person (if there is one) or yourself, start the stopwatch as soon as all the Thiosulphate is in the conical flask.
After you have started the timer watch the experiment as it takes place and look directly down from the top of the flask to the ‘X-tile’ and when you see the ‘X’ marked on the tile disappear stop the stopwatch. Write the time down in a table like the one shown at the bottom.
Wash out all the measuring cylinders and the conical flask but make sure there isn’t any water left in any one of the cylinders.
Then using one of the measuring cylinders measure 35cm3 of Sodium Thiosulphate, then get the other measuring cylinder and measure out 10cm3 of Hydrochloric acid after this we will measure 5cm3 of distilled water in the third measuring cylinder and add this to the Sodium Thiosulphate (so both the water and Sodium Thiosulphate added together will equal to 40cm3), after this put the 10cm3 hydrochloric acid in the conical flask, be careful again as after you have put the 10cm3 hydrochloric acid in the conical flask put all the Sodium Thiosulphate and water mixture in the conical flask and with the other person (if there is one) or yourself, start the stopwatch as soon as all the diluted Thiosulphate is in the conical flask.
After you have started the timer watch the experiment as it takes place and look directly down from the top of the flask to the ‘X-tile’ and when you see the ‘X’ marked on the tile disappear stop the stopwatch. Write the time down in the table.
Now repeat the experiment above with the water and sodium Thiosulphate mixture but instead of using 5cm3 of water and 35cm3 of Thiosulphate use the figures below in the same order as shown (make sure you wash out the cylinders every time):
- Measure 30ml of 0.2M sodium thiosulphate and 10ml of distilled water from the measuring cylinder.
- Measure 25ml of 0.2M sodium thiosulphate and 15ml of distilled water from the measuring cylinder.
- Measure 20ml of 0.2M sodium thiosulphate and 20ml of distilled water from the measuring cylinder.
- Measure 15ml of 0.2M sodium thiosulphate and 25ml of distilled water from the measuring cylinder.
- Measure 10ml of 0.2M sodium thiosulphate and 30ml of distilled water from the measuring cylinder.
- Measure 5ml of 0.2M sodium thiosulphate and 35ml of distilled water from the measuring cylinder.
Fair Test
To ensure that the test if fair I will control the following;
- The person conducting the experiment.
This will always be the same, because then the eyesight will be the same and the experiment will be more accurate.
- The equipment I will use.
All the equipment that I use will be washed after every experiment, and then re-used, so that the results cannot be affected by the varying of each measuring cylinder.
The volume of the hydrochloric acid will always be 10cm3 and the Thiosulphate and water mixture will always be 40cm3.
- The concentration of the acid and the sodium Thiosulphate
The concentration will be the same to allow the number of collisions in the reaction to be dependant for just the temperature.
This can affect the results, because if pressure is increased the rate of reaction will increase, because the particles are closer together meaning that it is easier for more effective collisions to take place.
- The temperature will always be at room temperature.
I will be varying the following;
This will be varied and must still have the same total volume for each experiment but only changing the concentration of Thiosulphate and water.
Safety Considerations
To ensure that the experiment is carried out safely, I will wash my hands after every experiment, safety goggles and overalls will be worn, and all chemicals will be handled with care as hydrochloric acid is an irritant. I will also ensure that the workbench is dry and free from all chemicals, as this could influence my results.
Treatment of Results
After I have obtained the results, I intend to place them in a results table. Using the results in the table, I will draw a graph that will show the reaction rate clearly.
Prediction (quantitative prediction)
A chemical reaction can only occur between particles when they collide (hit each other). Particles may be atoms, ions or molecules.
There is a minimum amount of energy which colliding particles need in order to react with each other. If the colliding particles have less than this minimum energy, then they just bounce off each other and no reaction occurs.
The faster the particles are going, the more energy they have.
Fast moving particles are more likely to react when they collide.
You can make particles move more quickly by heating them up (raising the temperature) or alternately you can increase the concentration like we are going to do:
Increasing the concentration (in solution).
Increasing the concentration of a substance in solution means that there will be more particles per dm3 of that substance.
The more particles that there are, the more will per second, and so the rate of the reaction increases.
In the reaction between sodium thiosulphate solution and dilute hydrochloric acid, I predict that if I increase the concentration of the Thiosulphate the faster the rate of reaction will be.
I also predict that if I double the concentration the rate of reaction will also double proportionally, this is because there is twice as much sodium thiosulphate.
This means there is a double the probability chance of collisions. So therefore if there are even more collisions between the particles then there will be an increase in the rate of reaction.
Planning (particle theory)
Factors that may affect the rate of reaction between the sodium thiosulphate and the acid are the temperature, the surface area (in a solid), the concentration, if there is a catalyst and if the solution is stirred.
The temperature may affect the rate because the particles will receive more energy and therefore move around faster and at a greater distance. This will mean more collisions will occur and they will be stronger.
The surface area might affect the rate of reaction because if many particles are in contact with the solution, more collisions can take place meaning that the reaction will be faster.
The concentration will affect the rate of reaction because if there is a large number of particles in the solution, there can be more collision meaning the reaction will be faster.
If a catalyst is added to the experiment the rate of reaction will be faster because the activation energy is lowered.
The last factor that may affect the rate of reaction between sodium thiosulphate and acid will be whether the solution is stirred. This may affect the reaction because if the solution is stirred particles can spread out easily and because the particles move further they can collide with other particles.
Range of experiments I will do
The range of experiments I will do, I have listed in a table below. The acid will stay constant at 10cm3 therefore we can worry less about changing the concentration of the acid and more about changing the concentration of the sodium thiosulphate.
This will probably increase the accuracy and reliability of the results making it easier o analyse.
These are the experiments I will do.
Approach to reliable results and results of preliminary work
Reliable results in any experiment if your doing it fairly should be obtained when you have done repeats for the experiments that way we can identify any anomalies which can then be removed.
Also, your results should be compared with other groups of sets of results to check for accuracy and reliability.
These are the results of my preliminary work
These were my results from my preliminary experiments
