Chemistry resources

Clarifications of Internally Assessed standards in Chemistry

NB: Evidence required for Achievement (or Merit) is also assumed for Merit (and Excellence).

90305 Version 2 (2.1) Carry out qualitative analysis

The standard involves identifying ions in solution. The intent of the standard is that, using a procedure provided by the assessor, students carry out the related practical work, record observations and make their own conclusions. The presence of an ion must be supported by all the required evidence.

For an ion to be correct, and contribute towards a grade, all the appropriate evidence is required. That is, for each ion, tests carried out, and observation s recorded, PLUS

• for Achieved: ALL precipitates formed by the ion identified (by name or correct formula)
• for Merit: Achieved criteria PLUS equations for all the precipitation reactions occurring for the ion (balanced, correct charges on ions)
• for Excellence: Merit criteria PLUS equations for all reactions involving complex ion formation for the ion (balanced, correct charges on ions)

eg Zn²+ ion, as the unknown ion:

• Achievement requires tests carried out, correct observations and all precipitates formed (with both aqueous NaOH and aqueous NH3) identified by correct name or formula.
• In addition, Merit requires correctly balanced equations for all the precipitation reactions occurring with both aqueous NaOH and aqueous NH3.
• In addition, Excellence requires correctly balanced equations for the reactions involving formation of complex ions with both aqueous NaOH and aqueous NH3.

Summary of requirements

Overall judgement is based on the number of ions correct with all the required evidence.

A majority of ions forming precipitates must be correct for A or M, PLUS a majority of ions forming complex ions correct for E.

Too many solutions containing , , or ions in an activity limits the opportunity for students to demonstrate evidence of ability to identify precipitates formed and write equations for precipitation and complex ion formation reactions.

90306 Version 2 (2.2) Carry out acid-base volumetric analysis

The standard involves carrying out an acid-base titration and calculating the concentration of the unknown solution.

• A practical analysis involving a non one-to-one stoichiometric relationship, e.g. titration of NaOH with , meets the requirements of the standard.
• If a one-to-one reaction is used in the practical analysis, a further non one-to-one reaction can be provided as an additional written exercise. Sufficiency requires both calculations (with units and significant figures) to be correct to achieve with Excellence.
• Judgement on accuracy and concordancy is based on the student choice of titres used.
• An error which shows a lack of understanding of the chemistry involved in the analysis is not a minor error.
• Where the error leads to a concentration which is not a sensible one, it is not a minor error.
• One trivial error in subtraction of titres may be ignored assuming it has no effect on the accuracy of average titre.
• Judgement on appropriate use of significant figures and units is only made on the final concentration determined.
• If the concentration of the unknown solution needs to be determined with three significant figures the concentration of the standard solution needs to be provided with this accuracy.
• The expected titre, and calculation of concentration of unknown solution, must be shown in the assessment schedule provided.

Summary of requirements

90763 Version 2 (2.3) Solve simple quantitative problems

The standard involves solving quantitative chemical problems. The step up in criteria is based on the complexity of problems solved.

• A suitable activity will include a range of types of problems. The explanatory notes provide some possible examples.
• An assessment activity needs to contain a variety of types of problem since evidence provided cannot be just 'more of the same'.
• Each type of problem suggested should be a stand-alone problem for the particular level of achievement.
• Data given in questions must be given with the accuracy required in the numerical answers. This is generally three significant figures.
• Use of significant figures and units must be appropriate over the whole activity where numerical answers are determined. Whether a quantitative problem is a simple one or a complex one, significant figures need to be appropriate for all numerical answers for students achieving at Excellence.
• Judgement on appropriate use of significant figures and units is only made on the final answer to the problem.
• Students can easily access the activities on TKI so the quantitative problems in these examples need to be changed to provide a fair assessment activity.

Summary of requirements

Last updated: 02 March 2010