Resources for Chemistry

Exemplars of Student Work

AS90694 Carry out an extended practical investigation involving quantitative analysis

Exemplar # 1 | Grade awarded: Excellence

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. Material referred to in the report is supported by the log book. Pages in the log book have been numbered to reference the material.

The log book shows all the initial thinking, development of the procedure using trials, data collected and related calculations and a repeat to check the reliability of the procedure. This is an extensive document involving 40 pages.

The report is a smaller document and the 11 pages provided could be considered perhaps longer than required. The bold words in the comments below show where key evidence is within the report.

Marginal aspects are

background information. This could include more information related to the reasons for degradation of Vitamin C over a period of time and therefore the relevance of the investigation.
preparation of sample. Detail in log book, minimal detail in report.
clarity of check for reliability of procedure. This was covered well, particularly in the log book, but it is difficult to find as it is not referred to in the method and is referred to late in the report.
measurement of time. Referred to in discussion, recorded in the log book. The graph would be more accurate if the time axis were units of hours rather than days.

Report

Report
	Page 1 Purpose: Meets the standard as the independent variable is storage time which can be measured. Background information on Vitamin C, a little limited. Further information is found on page 6.
	Page 2 Method: Final method described. Original procedure found is page 6 in log book. Some alterations suggested and trials carried out page 8 in log book. Modified procedure found on log book page 12. Making and standardising solutions referenced to page 21 in log book.
	Page 3 Results: recorded for the blank titration carried out. Detail referred to in log book and confirmed there. Detail of preparation of sample ideally should be in report but can be found on page 19 of log book. Implies that lemon juice was kept in the fridge but this could be clearer. Equations: Equations for reactions occurring are shown and used to show overall calculation relationship. Summary of collected data: Shown for the first values of the independent variable.
	Page 4 Summary of collected data: Shown for the remaining values of the independent variable. Reference to new standard solution and new blank titration. Details in logbook. Quantity of data: Meets requirements as 9 values of independent variable selected. Quality data: Meets requirements as difference between blank and sample titres over 16 mL. Sample calculations: All steps of calculation shown using data for two values of independent variable.
	Page 5 Summary of processed data: The summary of collected and processed data has been shown. Requirement for summary of collected and processed data is met although shown using two tables rather than altogether in one table. Data is correctly shown as a graph. Only one graph is required as these are the same. No equation for the graph is required. This can be ignored.
	Page 6 Conclusion: Valid conclusion stated. This has been underlined. Reference to actual values and decrease as mass per volume is not required. Relating results to background information: Discussion considers the use of making your own lemon juice, daily intake of Vitamin C, and how long the juice should be kept. Reactions of Vitamin C considered over time.
	Page 7 Controlled variables: Discussion of relevant variables. Confirmation that lemon juice was kept in the fridge and why it was kept here. Modifications made: Discussion of reason for changes made to the 'text book' analysis. Recognition of obtaining a titre size which shows quality data.
	Pages 8 to 9 Reliability of procedure: This should have been included in the method. Initially it was not obvious that a check for reliability of procedure had been done. Further detail in the log book from page 35 on. New sample prepared and new solution made. A repeat of 3 values of the independent variable carried out. Summary of processed data and graph showed similar trend to initial tests.
	Pages 9 to 10 Possible sources of error: A discussion of limitations and difficulties encountered which may contribute to possible errors. Note that this should not be based on errors that could have been overcome.
	Pages 10 to 11 Resources, references and bibliography: Although not stated as a requirement of the standard, it would be expected that the student acknowledges material that they have resourced.

Log Book
	Pages 1-4 This shows the student's first thoughts. Independent variable selected as temperature. Possible contexts considered, potential problems considered.
	Page 5 A suitable purpose decided. Values of independent variable considered. Questions related to control variables considered.
	Page 6 and 6a Standard method for analysis. This can be provided by the teacher.
	Page 7 Thoughts associated with what will be required.
	Pages 8-11 Some trialling is being done and related calculations
	Pages 11-14 Procedure modified and more trials carried out.
	Page 15 Procedure now thought to be established.
	Page 17 Some problems occurring and change to purpose is made.

	Page 19 New sample prepared.
	Page 20 New purpose stated. New solutions made.
	Pages 23-33 Experiments carried out.
	Page 34 This was a blank page. This was deliberately left blank to separate the checking the procedure section.
	Page 35-39 Checking the reliability of the procedure. New sample of lemon juice and new solutions made.

Exemplar # 2 | Grade awarded: Achievement

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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.

Exemplar # 3 | Grade awarded: Merit

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A report on the investigation has been presented along with a comprehensive log book (49 pages) 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:

list of possible investigations
plan and time frame
possible methods for determining amount of iron
trials carried out to test for iron(III) in spinach leaves
research on iron in foods and reasons for changing to amount of iron(II)
method of analysis using permanganate trialled
trials involving reduction of iron(III) to iron(II) and then determining amount of iron(II) in spinach
related calculations
final purpose and procedure decided with further trials and related calculations
making and standardising permanganate solution
preparation of sample
results and calculations for all boiling times
repeat of procedure with new samples and new standard
all calculations
comments reflecting on the investigation.

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 Merit are:

the error in processing of data as the percentage calculations are not correct. This has prevented a discussion of what was actually happening during the analysis that was carried out.
using the procedure given, as the amount of iron(II) is much higher than would be likely, the discussion needs to question the validity of this procedure. Something else must have been oxidised by the permanganate solution. As the research provided indicates that this may be due to the presence of oxalates in the spinach, the procedure used needs to have been considered and discussed further.

Report
	Page 1 Purpose stated. Background material described. This considers iron content in spinach and earlier related research. Also, information related to absorption by the body. Description of the method that will be used and chemistry related to this.
	Page 2 The procedure used is outlined. Preparation of sample is clearly outlined although measurement of water added is not carried out accurately. Procedure does not state concentration of sulphuric acid used although this can be found in the log book.
	Page 3 Detail of the preparation and standardising of permanganate solution. This does not have to be in the report and could be referenced to the log book.
	Page 4 Sample calculation using collected data. The calculation is correctly carried out to determine amount, and mass, of iron(II) in the 25 mL sample analysed. The equation involved in the analysis is shown and reacting mole ratio correctly used. However, the percentage calculation is incorrect. 100 g of spinach was cooked in 500 mL of water and a 25 mL sample of this water contained 58.7 mg. Therefore the 500 mL of solution (made from 100 g of spinach) would have contained 1.17 g iron(II). This is the iron(II) lost from the spinach rather than what is contained in the spinach. Therefore, mass lost is much larger than would be expected as it exceeds the mass of iron(II) found in spinach, according to the research data.
	Page 5 Calculation to determine concentration of the standard permanganate solution. This could remain in the log book and be referenced.
	Page 6 Summary of collected and processed data has been provided. Titration data in log book shows concordancy of titres used to determine average titre. While the trend is unchanged, the mass of iron(II) only relates to the 25 mL sample and percentage calculation is incorrect.
	Page 7 The conclusion could be based on the amount of iron(II) in the water analysed and this is increased as the boiling time is increased. That does mean the % of iron(II) in the water has increased but that is not what has been calculated. The discussion considers things that may have altered accuracy of result and compares data gained to background information. If the previous calculation had been carried out to correctly determine mass of iron lost from the whole 100 g sample, this would have led to questions about the procedure carried out.
	Page 8 Evaluation of the procedure used shows a repeat of the process that was carried out. Data relating to this is in the log book and shows a new sample of spinach being prepared and a new permanganate solution being prepared and standardised. A similar trend is found with the data collected.
	Pages 9 -11 Discussion on the reliability and accuracy of data related to the procedure carried out and discussion of why modifications were made to the original procedure. The presence of oxalates in spinach has been discussed and it is noted that oxalic acid will be oxidised by permanganate and that this may have altered the results. While this is the likely explanation for the impossibly high amount of iron(II) assumed to be present, the incorrect calculation has meant this has not been fully considered. Discussion related to both iron(II) and iron(III) and trials carried out to determine whether there might be iron(II) in the spinach.
	Page 12 A bibliography has been included.

Exemplar # 4 | Grade awarded: Not Achieved

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A report on the investigation 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:

initial ideas for the purpose and what would be required for the investigation
analytical procedures and lists of chemicals and equipment required
detail related to intended investigation
trials and associated notes including problems encountered
information on chemicals being used
continued trials and calculations
final procedure used, data from all titration carried out.

The cover page of the report has not been included since this did not contain any further information relevant to the standard.

The key issue preventing Achievement is that the calculation associated with the analysis involved is incorrect resulting in an incorrect amount of substance being determined. The errors involved here are significant.

In addition:

statement of purpose is marginal
there is no summary of collected and processed data as is required for Achievement. The summary includes only the collected data with respect to values of the independent variable. The processed data is the amount of substance determined
data collected is not quality data, as required for Merit, since the EDTA solution used has not been standardised
discussion does not meet the requirement for Merit.

Note that as there is no reason given as to why the calcium content in milk would change when a sample is heated, a teacher may suggest the student consider a different purpose.

Report
	Page 1 Purpose is not particularly clear as it does not state how 'heat' is being applied. This could be differing lengths of heating time of heating or exposure to different temperatures. Further on it is evident that the length of time of heating at boiling point is the independent variable. The purpose should be a short, concise statement. Background information is mostly not relevant. There does not appear to be an understanding of the role of the potassium hydroxide solution in the analysis. Most of the background information (continued on page 2) is related to the procedure rather than the purpose of the investigation. Relevant background material should be related to the reason (purpose) for doing the investigation.
	Page 2 A method is started on this page but it is a continued discussion related to why potassium hydroxide is to be used.
	Page 3 Describing a method and a procedure is a little confusing as they are the same thing. The final procedure used needs to be clearly stated, ideally step-by-step. This will include preparation of the sample as well as the analytical technique. The lack of clarity would make it difficult for the investigation to be duplicated by another person.
	Page 4 The term 'amount' is incorrectly used and this should be 'volume'. These results are the average titres for the different heating times. Titration data in the log book shows the full data and concordancy of titres gained, for each time, is appropriate. Graph again shows incorrect use of 'amount' and refers to a procedure line and a trend line. A procedure line is not meaningful. Rather than saying there is no trend, the data is showing no change in average titre.
	Page 5 The calculations are incorrect. A direct titration between the EDTA and calcium ions has been carried out. The average titre of EDTA used has not been used to determine amount of calcium ions as 50 mL has been used in this first step. This has negated the 50 mL of milk used in the next step so the assumed calcium ion concentration is the same as the concentration of the EDTA solution. In determining mg/L, of calcium the molar mass of EDTA has been used. These errors cannot be considered minor. Validation results are given but there is nothing to indicate what these actually are.
	Page 6 The conclusion is incorrectly interpreted as no trend. The trend is that there is no change in amount of calcium. Discussion does not suggest why the milk was frozen.
	Page 7 Aspects in the discussion related to change of temperature during the day and temperature of heating - having a range of 2 degrees Celsius could be considered minimal. Water was added to the milk before it was heated and there is a statement in the discussion saying that dilution with milk should be avoided. There is no rationale for this statement. Some evaporation of water will occur when the sample is heated and this has not been identified. While this will not be an issue for a specific heating time (since aliquot was measured after heating) a longer heating time will result in greater amount of evaporation.