ANIONS 3

• Group 3 anions are those ions whose calcium and barium salts are soluble but whose cadmium salts are insoluble in neutral or slightly basic solutions.
• No separation is involved in the analysis of this group.
• The tests for the three anions are made on separate portions of the group precipitate since they offer no interference with each other.
• reagent for precipitation of Group 3 anions: Cadmium acetate
• if you add cadmium acetate to sulfide, you will get a yellow color
• adding cadmium acetate to ferricyanide will give you orange color
• if you add cadmium acetate to ferrocyanide it will give you a cream, almost white color
• The color of your precipitate has an initial indication of your unknown sample.
• The precipitate is washed thoroughly to remove any contamination of the thiocyanate ion from Group 4 anions.
• We need to remove thiocyanate ion because it will interfere with the test for the ferrocyanide since both ions react with ferric ion, which is the identification reagent.
• glassware for sulfide ion: test tube
• Confirmatory reagent for sulfide ion: lead acetate
• positive indicator for sulfide ion: brown or black coloration
• The addition of hydrochloric dissolves the cadmium sulfide and liberates hydrogen sulfide gas.
• The hydrogen sulfide gas will be captured by the filter paper with lead acetate forming blackening of the filter paper due to lead (II) sulfide
• glassware for ferrocyanide ion: spot plate
• confirmatory reagent for ferrocyanide: ferric chloride
• positive indicator for ferrocyanide: prussian blue precipitate
• The addition of hydrochloric acid dissolves the ferrocyanide ions. Further addition of ferric chloride forms the dark blue precipitate, also called Prussian blue
• If green solution is obtained upon the addition of ferric chloride, the presence of ferricyanide is indicated
• confirmatory reagent for Ferricyanide ion: ferrous sulfate
• glassware for ferricyanide ion: spot plate
• positive indicator for ferricyanide: turnbull's blue
• The addition of Hydrochloric acid dissolves the ferricyanide ions. Further addition of Ferrous sulfate forms the dark blue precipitate, also called Turnbull’s blue