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Identifying Positive Ions

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Identifying Positive Ions Name:____________________________ Identifying Positive Ions In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. A group of students had four different colourless solutions in beakers 1, 2, 3 and 4, shown in the figure below. The students knew that the solutions were • sodium chloride • sodium iodide • sodium carbonate • potassium carbonate but did not know which solution was in each beaker. The teacher asked the class to plan a method that could be used to identify each solution. She gave the students the following reagents to use: • dilute nitric acid • silver nitrate solution. The teacher suggested using a flame test to identify the positive ions. Outline a method the students could use to identify the four solutions. You should include the results of the tests you describe. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ (6 marks) Marked by:_______________ Feedback Identifying Positive Ions Marks awarded for this answer will be determined by the quality of the written communication as well as the standard of the scientific response Poor Level 1 Level 2 Level 3 Understandi Basic Understanding Clear Understanding Detailed Understanding ng (1-2 marks) (3-4 marks) (5-6 marks) (0 marks) Grade 3-4 Grade 5-6 Grade 7-8 • Knowledge of basic • Knowledge of accurate • Knowledge of accurate information information information appropriately • Simple understanding contextualised • The answer is poorly • Clear understanding organised, with almost • Detailed understanding no specialist terms and • The answer has some supported by relevant their use demonstrating structure and organisation, evidence and examples a general lack of use of terms has been understanding of their attempted but not always • Answer is coherent and is meaning, little or no accurately, some detail in an organised, logical detail given sequence, containing a • The spelling, wide range of appropriate punctuation and • There is reasonable or relevant specialist grammar are very accuracy in spelling, terms used accurately weak punctuation, although there may still be some errors. • The answer shows almost faultless spelling, punctuation and grammar Examples of Chemistry points made in the response Test: add (platinum / nichrome) wire (for the flame test) accept any method of introducing the solution into the flame, eg a splint soaked in the solution or sprayed from a bottle Result: the sodium compounds result in a yellow / orange / gold flame or the potassium compound results in a lilac / purple / mauve flame student could state that potassium carbonate gives a different colour to the three sodium compounds as long as it is clear that the flame test colour comes from Na+ or K+ Test: add dilute nitric acid to all four solutions allow any acid Result: sodium carbonate and potassium carbonate will effervesce or sodium chloride and sodium iodide will not effervesce Test: add dilute nitric acid followed by silver nitrate Result: sodium chloride and sodium iodide produce a precipitate or sodium chloride produces a white precipitate and sodium iodide produces a yellow precipitate accept sodium carbonate and potassium carbonate do not produce a precipitate Total 6 marks .
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