CHILD ABUSE, CHILDHOOD & HISTORY
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Analysing; The Reaction of Hydrogen Peroxide and Iodide ions
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Introduction
Skill 3: Analysing; The Reaction of Hydrogen Peroxide and Iodide ions
Table of Results
Experiment | Volume of KI used (dm3) | Volume of water used (dm3) | Concentration of I- ions | Time taken for colour to appear (S) |
A | 5.0 x 10-3 | 0.020 | 0.02 | 9:56 |
B | 0.010 | 0.015 | 0.04 | 5:36 |
C | 0.015 | 0.010 | 0.06 | 4:07 |
D | 0.020 | 5.0 x 10-3 | 0.08 | 3:27 |
E | 0.025 | 0.000 | 0.1 | 2:40 |
We calculate the concentration of I- ions by following these stages (taking the hypothetical value of experiment A)
Number of moles of KI contained = volume x concentration
= 5.0 x 10-3 x 0.1
= 5.0 x 10-4 moles
= Number of I- ions contained in the solution
Concentration of solution = number of mols
Volume of solvent
= 5.0 x 10-4 / (25/1000)
= 0.02 mol/dm3
Thus I have calculated the other values, which appear on the table
Analysis
Derived from the rate equation
Log (1/time) = n log (volume of KI) + constant
We can calculate the rate
Middle
-2.53
C
-1.82
247
-2.39
D
-1.70
207
-2.31
E
-1.60
160
-2.20
Thus, we could derive the gradient of the graph, by drawing it, as seen upon the nest page.
We could also use the statistical method of finding the equation of the regression line, which is:
Y = a +bx (where y and x are the axis's)
B = (xI - x)(yI -y)
(xI - x)2
a = y - Bx
Where y = average of all y values
x = average of all x values
xI = x value
yI = y value
Therefore, when an equation is formed, we can mathematically derive the gradient, as the gradient of the graph, mathematically is the constant in front of x, providing y has no constants.
Thus B = (xI - x)(yI -y)
(xI - x)2
= 0.796
= 0.80
therefore, the order of reaction, with respect to the iodide ions is 0.80.
Maximum error of reading an apparatus = maximum error x 100
Amount read
Maximum error of 5 cm3 pipette = 0.1/ 5 x 100
= 2%
Maximum error of 10 cm3 pipette = 0.1/ 10 x 100
= 1%
Maximum error of burette = 0.15/25 x 100
= 6.0 x 10-3 %
Maximum error of measuring cylinder = 0.5/25 x 100
= 2%
Conclusion
There could have also been substances that were left in the beaker or pipette, thus the actual experiment that was performed did not include these leftovers. A way of avoiding this is to ensure that they would be "washed" and when transferring solution from a pipette, to ensure all the solution has come out, it would also be suggested to touch the surface of the solution with the pipette.
One way in which should not have affected the reaction, but probably did, is our concentration span, while waiting for the solution to turn colour, we became increasingly distracted by the surroundings, and hence, at times may have missed the actual time of which the solution changed colour, thus could have affected the results, even though in a very minor way.
Other ways of improving this experiment would include the use of a pipette instead of a measuring cylinder; even a burette would increase accuracy of the reaction, as a measuring cylinder is quite inaccurate. Another way of improving the reaction is by using a higher concentration of the solutions.
This student written piece of work is one of many that can be found in our AS and A Level Core & Pure Mathematics section.
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