3 Required practical 11: Identify transition metal ions

A-level Chemistry exemplar for required practical No. 11 Carry out simple test-tube reactions to identify transition metal ions in aqueous solution: An investigation of some transition metal compounds Most transition metal compounds are coloured. Some of them are used as dyes and pigments. A dye is a soluble coloured compound. A pigment is an insoluble coloured compound. Both dyes and pigments have to be resistant to chemical change. Four solutions, labelled P, Q, R and S, have been provided by a supplier as possible dyes.  You will carry out tests on these solutions.  You will record what you observe for each test.  You should ensure that you record observations on dropwise addition, on addition to excess and on standing.  Where no visible change is observed, write ‘no visible change’. In this task, you are not required to identify any of the solutions or any of the reaction products. Requirements You are provided with the following:  four solutions – labelled ‘Solution P’, ‘Solution Q’, ‘Solution R’ and ‘Solution S’  sodium hydroxide solution  sodium carbonate solution  silver nitrate solution  12 test tubes  7 dropping pipettes  test-tube rack  250 cm3 beaker  access to hot water  plentiful supply of distilled or deionised water. Suggested method Test 1(a) a) Place about 10 drops of solution P in a test tube. b) Add sodium hydroxide solution, dropwise with gentle shaking, until in excess. c) Do not discard this mixture. d) Repeat this test with solution Q and then solution R and then solution S.Test 1(b) a) Half fill a 250 cm3 beaker with the freshly boiled water provided. b) Allow the four test tubes containing the mixtures from Test 1(a) to stand in the beaker of hot water for about 10 minutes. c) While you are waiting, begin Test 2. Test 2 a) Place about 10 drops of sodium carbonate solution in a test tube. b) Add about 10 drops of solution P and shake the mixture gently. c) Repeat this procedure with solution Q and then with solution R and then solution S. Test 3 a) Place about 10 drops of solution P in a test tube. b) Add about 10 drops of silver nitrate solution and shake the mixture gently. c) Repeat this procedure with solution Q and then with solution R and then solution S. d) Allow the four test tubes to stand for about 10 minutes. Sample results Test 1(a) and (b) P Q R S Initial blue solution yellow solution light blue solution pale green solution Add NaOH white precipitate orange/brown precipitate deep blue precipitate grey/green precipitate On standing in hot water green solution no visible change no visible change no visible change Test 2 P Q R S Addition of sodium carbonate grey precipitate orange/brown precipitate and effervescence blue/green precipitate grey/green precipitate Test 3 P Q R S Addition of silver nitrate no visible change white precipitate white precipitate light brown precipitate