AS 91910 annotated exemplars

This annotated exemplar is intended for teacher use only. Annotated exemplars are extracts of student evidence, with commentary, that explain key parts of a standard. These help teachers make assessment judgements at the grade boundaries.

Download all exemplars and commentary [PDF, 1.8 MB]

TKI Chemistry assessment resources (external link)

For Excellence, the student needs to carry out a comprehensive practical investigation into a substance present in a consumer product using quantitative analysis.

This involves accurately determining the concentration of the substance in the consumer product (including correct use of significant figures and units), justifying how modifying the consumer product sample and/or titration procedure improved the validity and accuracy of the investigation, and evaluating the outcome of the investigation in relation to the consumer product.

This student has modified the consumer sample and collected, recorded and processed quality data. The concentration of the substance was accurately determined (1).

The learner has justified why the consumer product was modified based on the trials (2), and there is some justification of showing how the procedure used improved the accuracy and validity (3). The learner has evaluated the outcome of the investigation (4).

For a more secure Excellence, the student should clearly show how the modifications resulted in an increase in validity and accuracy. For example, the justification of the rinsing of the glassware should explain how the flask only needs to be rinsed with distilled water, but the burette and pipette get rinsed with distilled water and then the solution that is used in them. This can then be used to justify an increase in the validity/accuracy of the investigation (5).

For Merit, the student needs to carry out an in-depth practical investigation into a substance present in a consumer product using quantitative analysis.

This involves using results from the trials to develop a valid plan to modify the consumer product sample and/or titration procedure, and collecting, recording and processing quality data that enables a valid conclusion to be reached. This also involves accurately determining the concentration of the standard solution and the substance present, as well as explaining how the control of variables improved the quality of the investigation.

This student has developed a valid plan based on the results of the trials (1) and collected, recorded and processed (2) quality data to make a valid conclusion (3). The student has explained how diluting the consumer product (4) and the rinsing of the glassware (5) improves the quality of the investigation.

To reach Excellence, the student could explain how aspects of the investigation improved the validity and accuracy of the investigation. For example, linking the control of the amount of indicator to the possible effect on the colour change at the endpoint, or explaining how leftover ammonia/sulfuric acid in the flask could change the concentration of the sample and its effect on the titres, would be required to show justification of the titration procedure (6).

For Merit, the student needs to carry out an in-depth practical investigation into a substance present in a consumer product using quantitative analysis.

This involves using results from the trials to develop a valid plan to modify the consumer product sample and/or titration procedure, and collecting, recording and processing quality data that enables a valid conclusion to be reached. This also involves accurately determining the concentration of the standard solution and the substance present, as well as explaining how the control of variables improved the quality of the investigation.

This student has developed a valid plan and collected, recorded and processed quality data (1) to make a valid conclusion (2). The student has explained how the removal of the air bubble improves the quality of the investigation (3).

For a more secure Merit, the student should show correct working for either the concentration of the secondary standard solution or the concentration of the ethanoic acid (4). The learner could also further explain how using specific lab equipment improves the quality of the investigation (5).

For Achieved, the student needs to carry out a practical investigation into a substance present in a consumer product using quantitative analysis.

This involves developing a workable plan to determine if the consumer product and/or titration procedure require modification, and collecting, recording and processing sufficient data to enable a conclusion to be reached. This also involves determining the concentration of a substance relevant to the investigation (using stoichiometric principles and both relationships n=m/M and c=n/V) and describing how significant variables were controlled.

This student has developed a workable plan (1) and collected, recorded and processed sufficient data for a conclusion to be reached (2). The learner has calculated the concentration of a substance (3) and described the significant variables that were controlled (4).

To reach Merit, the student could explain how the control of the significant variables improved the quality of the investigation. For example, explaining that all glassware is rinsed with distilled water first, and then the burette and pipette are rinsed with the solution to be added to ensure there are no contaminants that could react, and the concentrations of the solutions in the pipette and burette are kept constant. This ensures the titre values are accurate and concordant (5). 

For Achieved, the student needs to carry out a practical investigation into a substance present in a consumer product using quantitative analysis.

This involves developing a workable plan to determine if the consumer product and/or titration procedure require modification, and collecting, recording and processing sufficient data to enable a conclusion to be reached. This also involves determining the concentration of a substance relevant to the investigation (using stoichiometric principles and both relationships n=m/M and c=n/V) and describing how significant variables were controlled.

This student has developed a workable plan and collected, recorded (1) and processed sufficient data for a conclusion to be reached (2). The learner has calculated the concentration of a substance (3) and has described the significant variables that were controlled (4).

For a more secure Achieved, the student could show the correct calculation using n=m/M. The student has got the correct working for n=m/M but the wrong answer for question 1 (5). The conclusion could also refer to the concentration that was calculated for the consumer product.

For Achieved, the student needs to carry out a practical investigation into a substance present in a consumer product using quantitative analysis.

This involves developing a workable plan to determine if the consumer product and/or titration procedure require modification, and collecting, recording and processing sufficient data to enable a conclusion to be reached. This also involves determining the concentration of a substance relevant to the investigation (using stoichiometric principles and both relationships n=m/M and c=n/V) and describing how significant variables were controlled.

This student has developed a workable plan and collected, recorded (1) and processed sufficient data for a conclusion to be reached (2). The learner has calculated the concentration of a substance (3) using stoichiometric principles (4) and both relationships n=m/M (5) and c=n/V.

To reach Achieved, the student should describe how significant variables were controlled. For example, describing what the different glassware was rinsed with, and how the use of white paper behind the glassware (burette) along with taking the reading while being at eye level and from the bottom of the meniscus. The statements used to describe the control of the significant variables need to be specific to the investigation rather than generic statements (6).