You are required to investigate seven inorganic compounds. Your test-tube rack is numbered 1 to 9.Two of the positions are empty.Each of the seven test-tubes provided contains only one compound in aqueous solution. Using only these solutions, pH indicator paper, and test-tubes, you are to identify as many of the ions present as you are able. For your information, record in the table the observations you make on mixing the solutions. Use the following symbols:
elimination reactions: ↓ precipitate; ↑ gaseous product;
↓s precipitate soluble in the excess of a precipitating agent.
colours: w - white or colourless, b - blue, g - green, y - yellow, p - pink, r - red, br - brown. pH: a - acidic, b - alkaline, n - neutral.
Equipment:
A home-made rack contained 9 test-tubes with the unknown solutions, 30 empty Wassermann-tubes and one small beaker containing the pH indicator paper. Into each solution a dropper was inserted, and thus, the test-tubes need not to be removed from the rack while handling them. According to the original plan the following nine unknown solutions were expected to be given to the participants:
CoCl2,Fe( SCN)3, NH4OH,KI, AgNO3, Na2HAsO4,HgCl2, NiCl2,CuCl2.
During the discussion of the International Jury it became known that in some countries the corresponding laws forbid the pupils in secondary schools to handle mercury and arsenic compounds. For this reason these two compounds were removed from the rack and consequently the number of ions to be detected - and the marks available - were reduced to 12 (from the original 15). (Under these conditions the alkali and nitrate ions cannot be detected.)
The order of the test-tubes varied individually,but the first two contained invariably red solutions(CoCl2 and Fe( SCN)3), while the last two were the green NiCl2 and CuCl2 symbolizing the Hungarian national colours, red-white-green