Presentation on theme: "Level 2 AS90305 (2.1) - Carry out a qualitative analysis (Version 2) Exemplars of Student Work The following exemplars are designed to show examples of."— Presentation transcript:
Level 2 AS90305 (2.1) - Carry out a qualitative analysis (Version 2) Exemplars of Student Work The following exemplars are designed to show examples of Not Achieved, Achieved, Merit and Excellence responses for this Achievement Standard. Refer to the sample pages for detail related to judgements made. Mostly activities used contain eight unknown ions. If at least six of these ions involve precipitation, evidence for Achievement will require five ions to be correct (with all precipitates formed by these ions identified), evidence for Merit will require five ions to be correct (with correct equations written for all precipitation reactions involved for these ions). If at least three of the ions involve complex ion formation, overall, six ions correct (correct equations for all precipitation and complex ion formation reactions) will provide evidence for Excellence.
Exemplar 1: Not Achieved This is a clear Not Achieved sample. Seven of the eight ions have been correctly identified. Tests carried out, and observations made, have been clearly recorded. However, the precipitates formed during the analysis have not been correctly identified. All precipitates formed by an ion need to be identified, by correct name or formula, for the ion to contribute evidence towards Achievement..
Exemplar 2: Achieved (low) This is a ‘just’ Achieved sample. Two ions are incorrect. A further ion is correct but is not supported by the evidence recorded. Task 3, the presence of a zinc ion has not been eliminated since there is no indication of excess aqueous ammonia being added. Neither zinc ions nor aluminium ions will precipitate with sulfuric acid. The last test only shows the solution cannot contain lead(II) ions. The remaining five ions have sufficient evidence although name and formula for precipitates are not always both correct. Task 6, the formation of a blue precipitate with sodium hydroxide solution is sufficient to show the presence of copper(II) ions since none of the other possible cations will form a blue precipitate. Recording the colour of the precipitate is essential.
Exemplar 3: Achieved (solid) This is a good Achieved sample. The eight ions are all correctly identified. However, only four ions provide evidence towards Merit as precipitates formed between lead(II) ions, and zinc ions, with aqueous ammonia have not all been correctly identified and precipitation equations written. A judgement of Merit requires five ions to be correct with all the precipitation equations correctly written.
Exemplar 4: Merit (solid) This is a sound Merit. All ions have been correctly identified with tests carried out and observations recorded. Five ions provide evidence towards Merit as all precipitation equations involved have been correctly written. Incorrectly written equations, such as in Task 3, further demonstrate that the student is not at the level required for Excellence.
Exemplar 5: Merit (high) This is a strong Merit. All ions have been correctly identified with tests carried out and observations recorded. Only issue with the activity is a repeated problem that complex ion equations involving ammonia have not been balanced. This results in three ions not having all the required evidence for Excellence. That is, overall, only five ions have all the required evidence. In addition, since five ions in the activity involve complex ion formation, three of these must be correct, with all the required evidence, for Excellence. Only two ions meet this requirement.
Exemplar 6: Excellence (solid) This is a sound Excellence. All ions have been correctly identified with tests carried out and observations recorded. Three ions of the four ions with opportunity for Excellence have all the required evidence. (A copper(II) ion can be identified using only aqueous ammonia.) The only error is the unbalanced equation for the reaction of silver chloride with aqueous ammonia.