What this standard actually asks for

How this standard is assessed

• AS91911 is internally assessed: you follow a supplied identification procedure on a real sample, record what you see, and write a report.
• The chemistry is not the hard part. The reporting is, because each grade asks for something specific from the same set of observations.

The criteria, in plain words

Grade	What you must do
Achieved	Collect primary data using the procedure; identify the species by matching your data to the procedure; link the species to the compound in the sample; describe the significance of one species for people and/or the environment
Merit	Explain the identification by linking your data to the procedure; write relevant equations for all the changes occurring; explain the significance
Excellence	Justify the identification by linking secondary data and chemical principles to the reactions occurring; discuss the significance

What "primary data" means

• Primary data is data you collected yourself, by doing the tests.
• It must be recorded as observations, not conclusions.
  • Conclusion, not data: "Cu²⁺ present."
  • Data: "On adding NaOH(aq) dropwise, a pale blue precipitate formed. It did not dissolve in excess NaOH. On adding NH₃(aq) in excess, it dissolved to give a deep blue solution."
• Record negative results too. "No precipitate formed with BaCl₂" eliminates sulfate, and eliminations are half of an identification.

What "secondary data" means

• Secondary data is information you did not generate: the solubility rules, tables of complex ion formulae and precipitate colours, a functional group reaction map, or scientific literature.
• Excellence requires you to use it explicitly, not just have it available.
  • Weak: "The precipitate was blue so it was copper."
  • Strong: "The solubility rules state that all hydroxides are insoluble except those of Group 1, so the precipitate formed on adding OH⁻ must be a metal hydroxide. The colour table identifies pale blue as Cu(OH)₂, and the dissolution in excess ammonia is consistent with the formation of the tetraamminecopper(II) complex ion."

Two species, one sample

• The clarification requires at least two chemical species to be identified.
• They must come from one sample, though you may split that sample into separate portions and test each separately.
• In practice this usually means one cation and one anion, which together identify the compound.

The purpose and context

• Your investigation needs a stated purpose, and the significance you discuss must relate to it.
• Good contexts give the significance something to attach to:
  • Testing a water sample from a stream near a road or farm.
  • Testing an unknown white powder found in a school laboratory.
  • Testing a fertiliser or a soil extract.
  • Testing runoff from a galvanised iron roof.
• The purpose sentence should name the sample, the question and why it matters: "To determine which ions are present in water collected from a drain below a galvanised roof, in order to assess whether the runoff could be harmful to aquatic life in the stream it feeds."