(ag) (ag) (aq) (aq) (s) (g)
My INPUT variable in this experiment, will be the different concentration of Sodium Thiosulphate. To keep this investigation thoroughly fair, the concentration of Hydrochloric Acid shall remain constant throughout, and there is no catalyst to be added. . As the concentration increases, the time for the reaction decreases. If we double the concentration, we double the number of collisions. This is because we double the number of particles, therefore, double the reaction. The concentration will be varied according to this dilutions table:
The OUTPUT variables that will be kept the same, would be the amount of Hydrochloric Acid used in the solution. The surface area will remain constant.
Adding a catalyst to the experiment, will increase the speed of the reaction, but a catalyst will not be added to the solution.
These variables will stay constant throughout the investigation.
The Prediction.
I expect that the more Sodium Thiosulphate that Is contained in the solution, the faster the reaction will be. As the concentration increases, the time for the reaction decreases. If we double the concentration, we double the number of collisions. This is because we double the number of particles, therefore, double the reaction.
I envisage this because of preliminary work. In the preliminary experiment, I used sulphuric acid and magnesium to investigate the rate of reactions. I used different concentrations of sulphuric acid and recorded the times and rates of each reaction which are as follows:
When the concentration of the sulphuric acid doubles so does the rate of the reaction. When the concentration of the sulphuric acid doubles so does the rate of the reaction, as shown on the graph. As the concentration doubles, (0.5M to 1M), the rate of the reaction doubles (0.01sec-1 to 0.02 sec-1 ), and I predict the similar results from this investigation.
Page 2
The Method.
List of equipment;
1 beaker
1 pepet
1 pair of safety goggles
1 stop clock
1 square piece of card with a distinct X marked on.
The technique to use for my investigation is as follows:
- Firstly put your safety goggles on! Add Sodium Thiosulphate to Hydrochloric Acid, regarding to the dilutions table on PAGE 1, in turn. I.e. Do one row of dilutions at a time. Start the clock once the solution is created in the beaker.
- Place the ‘X’ card underneath the beaker. (So you can see it.)
- Start the clock once the solution is created into the beaker.
- Monitor the solution from above. Be wary of toxic gases which are released from the investigation.
- When you cannot see the X through the base of the beaker, the reaction is complete. Stop the clock and note down the time to two decimal places, on a table the same as the results table attached.
- Empty the solution into the sink, rinse the beaker and instruments you have used thoroughly, ready to use again.
- Rinse out the apparatus used before attempting the next experiment. Carry out the next rows on the dilutions table, and follow the method from number three.
Safety
During this experiment, the investigator must follow strict safety rules. These are the same as regular lab rules.
- ALWAYS wear safety goggles throughout the experiment. NEVER remove them unless you are away from hazardous chemicals
- Take care when transferring chemicals into containers. If you spill any on yourself, IMMEDIATELY rinse the affected area with water, and report this to your teacher. If you spill any chemicals on the floor or bench, ask you teacher to clear it away.
- DO NOT leave chemicals or instruments close to, or at the edge of your workspace.
- DO NOT RUN in the laboratory, to prevent you or another student coming into contact with chemicals.
These rules must be followed throughout tour experiment, to allow you and other students to carry out the experiment safely and accurately.
Page 3
Measurements, Observations and Recordings.
I will measure the speed in which the reaction takes place by timing it from the second it enters the beaker, to the point where you cannot see the ‘X’ card through the bottom of the beaker.
I will record the results onto a table. Results will be taken three times (the amount of times is up to the investigator) then an average will be calculated.
The average can be calculated by adding the three results together, then dividing by three, or however many times you experimented.
( e.g. 34.50 + 31.22 + 30.13 x 3 = 31.95 )
Conclusion
I have found out from this investigation, that the more Sodium Thiosulphate you add to the solution, the quicker the reaction is. This is beacause I increased the amount of Sodium Thiosulphate, which increased the concentration, and the rate of reaction. If the concentration is doubled, there are twice as many particles, and twice as many which have more energy than the activation energy barrier. Therefore the reaction is increased and the rate is doubled.
The results support my conclusion:as the rate increases so does the concentration because there are more particles with more energy than the activation energy barrier. I predicted this, and when the concentration doubles so does the rate due to twice as many particles with more energy than the activation energy barrier, which I also predicted.
Results.
A line of best has been added to my graph. I noticed that there is a pattern to the
average results I gained. The line of best fit on the graph, goes up in a regular curve. There are no anomalous results.
My hypothesis is accurate to the results I gained. I predicted that the more Sodium Thiosulphate there was in the solution, the speedier the reaction would be.
Evaluation.
I think, the way I carried out this investigation was extremely fair and accurate. The variables were maintained to a high standard. My evidence should be valid for this investigation.
I believe the results I have gained from this experiment, where found accurately and fairly. The results, could have been more accurate, if I repeated the experiment a further two times.
My results are reliable enough to place them onto a graph with a line of best fit, which enabled me to come to the conclusion that if you double the concentration of the solution, the rate of the reaction is also doubled.
The method used to conduct this experiment, was effective.
There were no anomalous results, which is what I expected, but did not predict. I found keeping the output variables constant difficult because I had to keep checking the amount of solution used was correct to the units necessary.
