Level 2 90694 (3.1) - Carry out an extended practical investigation involving quantitative analysis

(Version 2)

Exemplars of Student Work

Exemplar 2: Achievement

A report on the investigation carried out has been presented along with a log book which includes the work carried out over a period of time.

The log book has not been included with the exemplar material but included the following:

•purpose and ideas of what the dependent and independent variable would be

•analytical procedure including chemicals and equipment required

•making the iodate solution required

•trials and associated notes including problems encountered with endpoint

•revised method and trials

•calculations using trial results, further problems considered

•more trials and calculations

•new method and making solutions required

•data from all titrations carried out

•calculations using collected data

•information on chemicals being used

•continued trials and calculations.

The cover page of the report has not been included since while this contained the purpose of the investigation, it did not have any further information relevant to the Standard.

The key issues that limit the judgement to Achievement are:

•the description of procedure used, as this would not allow the investigation to be duplicated

•calculation of concentration of iodate solution was not done accurately (however, this may have been considered borderline if other requirements of Merit had been met)

•the discussion of reliability of data lacks specific detail

•relevant background material is quite limited.

In addition, it is not clear that other sufficient variables have been controlled. There is no detail related to this in the log book. With respect to this aspect, the judgement of Achievement could be considered borderline.

Report

Page 1

Purpose stated. Background material is given, but this is limited. This should be related more to the reason (purpose) for doing the investigation. Relevance of Vitamin C in terms of dietary requirements described. Oxidation of Vitamin C considered using atmospheric oxygen.

Page 2

The actual sample used has not been stated. Samples of different commercial orange juice could be significantly different. A procedure states that identical cups, and the same volume of juice was used, but does not state what the cups were or what this volume actually was. While the procedure recognises that the samples need to be stored under the same conditions, how this was achieved has not been described.

The concentration of the iodate solution calculated has been rounded and this should have been 0.000748 mol/L. While this is a constant factor and will not affect a possible trend, it does mean that calculated data will not be quality data.

This lack of detail in the procedure means that it would be difficult for someone to duplicate the investigation as is required for Merit.

Page 3

The results are the average titres for the different lengths of time. Titration data in the log book shows the full data and concordancy of titres gained, for each time, is appropriate.

Page 4

Sample calculation using collected data has been carried out. This has been related to reactions occurring during the analysis.

Summary of collected and processed data has been provided. However, the mass of Vitamin C has not been linked to a volume of juice. It is the mass in a 20 mL sample of the juice.

Page 5

While a graph is not a requirement of the standard, it does show processing of data. However, a linear relationship is not necessarily valid. The conclusion is not worded particularly well and the second part of the statement is all that is required.

The first aspect of the discussion is vague as while it states that factors need to be controlled, how this is achieved is not described.

Page 6

The discussion includes a reference to freezing the samples but this was not included in the procedure. There is no justification for the claim that freezing will give more accurate and reliable results.

A comparison to a method that was not even considered (no detail related to this in the log book) is irrelevant and again there is no justification for the claim of more reliable results.

Comment related to use of iodine shows a lack of understanding of the procedure since iodine was not used. Potassium iodide was the substance used.

The significance of the conclusion should be related to the purpose of the investigation and this has not been done.

Page 7

A bibliography has been included. While this is not a requirement of the standard, it should be an expectation as it allows the assessor to verify material used. Lack of such would not affect judgement on the work presented.