17.20—Understand, in terms of the relevant E values, that the dichromate(VI) ion, Cr2O2- i can be reduced to Cr3+ and Cr2+ ions

Understand, in terms of the relevant E values, that the dichromate(VI) ion, Cr2O2- i can be reduced to Cr3+ and Cr2+ ions using zinc in acidic conditions ii can be produced by the oxidation of Cr3+ ions using hydrogen peroxide in alkaline conditions (followed by acidification).

Use —understand, in terms of the relevant e values, that the dichromate(vi) ion, cr2o2- i can be reduced to cr3+ and cr2+ ions to connect the rule to the data and decision in the question.

This matters because —understand, in terms of the relevant e values, that the dichromate(vi) ion, cr2o2- i can be reduced to cr3+ and cr2+ ions determines what can be inferred or chosen; begin with the stated conditions and keep the conclusion tied to the evidence.

Example: apply —understand, in terms of the relevant e values, that the dichromate(vi) ion, cr2o2- i can be reduced to cr3+ and cr2+ ions to one small, clearly defined case, show the key step or comparison, and explain the result in words.

Boundary: —Understand, in terms of the relevant E values, that the dichromate(VI) ion, Cr2O2- i can be reduced to Cr3+ and Cr2+ ions is not a universal recommendation. Check the syllabus scope, assumptions, units and the limits of the evidence before generalising.