conc.�✗ vol.✔ conc.✔ vol.✔
3- Used Equipments
● Conical flasks (5 pieces)
● Pipette (5 cm3 capacity)
● Measuring cylinder (50 cm3 capacity)
● Safety goggles (for eyes protection)
● Stopwatch (to measure the time needed for the reaction)
● White paper with a black cross
● Reagent bottle containing Na2S2O3
● Reagent bottle containing HCl
Apparatus
- Procedure
I will be measuring the rate of reaction of sodium thiosulphate and hydrochloric acid. In this experiment, there are different variables, including concentration that may be used to see the change in rate of reaction. I will be performing an experiment changing the level of concentration of sodium thiosulphate five times, and each experiment will be repeated three times and an average will be taken to confirm the accuracy of the results. Firstly, I will measure out the volume of Na2S2O3 and HCl. The beaker will then be placed on the marked paper. Next, the hydrochloric acid will be added to the Na2S2O3. At this point, the stopwatch will be started, and then the time should be recorded for the cross to disappear, whilst being stirred. This will then be repeated four more times, with the concentration of Na2S2O3 decreasing in measurements of 10 cm3. Safety goggles will be worn throughout experiment, as a safety precaution. Two people will perform this experiment, in order to take readings more accurately, (one to mix substances, the other to operate the stopwatch).
Five experiments are going to be carried out using different concentration levels of Na2S2O3 by:
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In the 1st conical flask place 50 cm3 of Na2S2O3 measured by a measuring cylinder.
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In the 2nd conical flask measure 40 cm3 of Na2S2O3 and add water until the final volume will be 50 cm3. This gives a concentration of 0.24 mol/dm3.
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In the 3rd conical flask measure 30 cm3 of Na2S2O3 and add water until the final volume will be 50 cm3. This gives concentration of 0.18 mol/dm3.
- Change the conc. in the next two flasks as shown above.
To make it a fair test by using the same conditions:
- Initial temp. (Room temperature).
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Volume of sodium thiosulphate. (50 cm3 by measuring cylinder).
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Volume of HCl. (5 cm3 by a pipette)
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Concentration of HCl. (2 mol/dm3)
Variables:
The concentration of Na2S2O3 will be changed in each experiment.
It has been decided that a concentration of no less than 0.06 mol/dm3 will be tested because any lesser concentration would probably take longer time. It has been decided that 2.0 ml of HCl and 0.3 ml of Na2S2O3 will be used.
- Precision
I will be performing an experiment changing the level of concentration of sodium thiosulphate five times, and each experiment will be repeated three times and an average will be taken to confirm the accuracy of the results. The paper that will be put under the conical flask that conains the cross, there should be a contrast between the black cross and the white paper in order to make the cross quite obvious. I will Leave the conical flasks for about 30 minutes before mixing the reactants reagent in order to have the same initial temperature (room temperature). I will not hold the conical flasks with your hands during the experiment to avoid heat transfer. The stopwatch will be started at the exact time as we put HCl into the conical flask.
7- Prediction
I predict that as the concentration of Na2S2O3 increases, the rate of reaction will increase. I predict this, because on increasing the concentration of the reagents, there will be bigger number of colliding particles per unit volume, so there is more frequency of successful collisions, and the reaction goes faster decreasing the time needed to obscure the cross. If the concentration of Na2S2O3 doubles, I predict that the rate of reaction will also double.
8- Resources
- http://www.edexcel.org.uk
- http://www.essaybank.co.uk./GCSE/chemistry_coursework
- Dr Nabil Sobhy, chemistry notes OL, Dar Eltarbiah, Year 2002-2003, page 118, 122,123.
II. OBTAINING EVIDENCE
Precautions
(a) For personal safety
● Wear safety goggles to protect your eyes from chemical splashes.
● Taking care when handling chemicals, particularly Hydrochloric acid because it is a corrosive.
(b) For accurate results
● There should be a contrast between the black cross and the white paper in order to make the cross quite obvious.
● Leave the conical flasks for about 30 minutes before mixing the reactants reagent in order to have the same initial temperature (room temperature).
● Don’t hold the conical flasks with your hands during the experiment to avoid heat transfer.
● The stopwatch must be started at the exact time as we put HCl into the conical flask.
I am sure that I have enough evidence to allow me to draw a conclusion. This means that I have large number of readings. My evidence is quiet good that I am sure of the consistency of my results, that nothing of them varies a lot, then I will not repeat any of the readings.
Results
The table of results below shows the followings:
III. ANALYSING EVIDENCE
Graph “A”:
The graph shows that the higher the concentration, the shorter the time needed to obscure the cross and vice versa.
My graph is a smooth one, which means that none of my results are odd.
Graph “B”:
The general trend indicates that the relation between the concentration and the rate of reaction is direct, so the higher the concentration, the faster the rate will be and vice versa.
My line is of best fit, and passes through the origin.
Conclusion:
I have found that and my results show that as the concentration increases, the time needed to obscure the cross is less and the rate of reaction is faster. This is because as the concentration increases, there would be more particles. They collide successfully and more frequently, thus the reaction goes faster; this is applied or based on the theory of “The Collision Theory”. This conclusion supports my prediction and proves its reliability.
IV. EVALUATING EVIDENCE
The procedure used was carried out well, and the results obtained were within predicted parameters, but it could have been improved, and these improvements will be listed later. The results are mainly good, and this could mean that the experiment was done perfectly. Although all the average times and rates of reaction conform to a pattern, they are not all evenly spaced, and are therefore probably not perfect. The results could be correct, but the results did not appear to be exactly uniform.
I believe that I do have an accurate set of results and that I do have enough results to be sure about my conclusion. My results are accurate because when I read the collision theory it matches exactly my results.
I do not have any anomalies results, which do not fit in the pattern because my predictions coordinated with my results very well.
My method of carrying out the experiment was fairly accurate. I made sure to wash the beakers carefully for the two levels of concentration. The second experiment, I measured the same amount of solution in each time and stopped the stopwatch as soon as I observed the cross disappearing. I think that I should have used five different beakers for the five different concentrations because this would be more accurate, fair as the beakers will be dry.
If I was to do the experiment again, I could improve the accuracy and reliability of the results by having a range of different concentrations. Also I could use the same amount of beakers for the number of different concentrations I used.
If I had more time, I could do additional experiments to investigate another factor such as the effects of temperature on the rate of reaction.
Improvements that could be made to this experiment:
To repeat this experiment several times and record more averages in order to obtain a higher degree of accuracy.
In my experiment, temperature and exact quantities could not be possibly obtained. On the whole, I believe this experiment was carried out to the best of my abilities, and is the optimum performance using all possible resources and time available. The results obtained, which seem reliable, supported my predictions.
