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%

Maximum error from apparatus reading = sum of maximum errors

= 2% + 2% + 1% + 6.0 x 10-3 %

= 5.006%

Skill 4: Evaluating; The Reaction of Hydrogen Peroxide and Iodide ions

Look at your graphs and comment on your results. Are you lines of best fit good enough for you to extrapolate the confidence? Are there any anomalous results? Suggest 1 possible reason for your anomalous result even if your results are within tolerance!

I have attempted my best to extrapolate the line of best fit, by not actually drawing the line of best fit, but calculating and predicting it statistically using the 'regression line' equation. Calculating the regression line includes plugging in all the obtained results in to the following equation:

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

thus, we can find the equation of the regression line (the line of best fit) and not only accurately extrapolate, we can accurately estimate or predict the value at a certain point using the line equation, by plugging in different values of x. However, the regression line could only have been accurate for the given data, and anything outside the given data could have been out of the trend, thus, we cannot say that the estimation from the regression line is correct, we can only minimise the inaccuracies from extrapolating the regression line.

There is one result that appeared to be anomalous when observing the graph. The second reading appeared to be slightly off the regression line, but nevertheless still within the trend of the slope of the graph. This slight anomalous result could be due to the fact that the solution used was not exactly the same, which is because of the nature of Hydrogen peroxide, which decomposes into water and oxygen relative quickly, proven by the fact that bubbles appeared in the H2O2 solution.

This reaction is first order with respect to the concentration of iodide ion. Calculate the percentage difference between your value for the order and the correct value

Difference of my value with the data = 1 - 0.80

= 0.20

Percentage of data value = difference x 100

Data value

= 0.20/1 x 100

= 20 %

Comment upon the magnitude of the difference between the correct value and your calculated value.

There is quite a considerable difference in the magnitude of my results with the data source. An inaccuracy of 20% is far more than the "allowed" error of 5.006%, which would be due to reading error. Thus we can conclude that the main error in this experiment is not laid on the reading error.

The considerable difference of the values also can make the data, somewhat of less reliability, as the value is not as close as we would have hoped it to be. This could be due to other different experimental errors, such as loss of solution when transferring, the decomposition of solutions and much more.

Identify 2 sources of error in this experiment. Suggest one improvement to minimise each source of error.

The main source of error seems to lie upon the nature of both solutions used. Hydrogen peroxide has a tendency to decompose to hydrogen and water after a while, hence the fact that the solution must be made as close to the experiment as possible. The starch solution would precipitate, had it been left too long and the iodide solution would turn yellow. All this is accountable to the time that we need to complete this experiment, the quicker we finish the experiment, the fresher the solutions would be and thus, less chance that the solutions have decomposed.

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.