Non-metal Ions Negative Ions Identifying Anions Non-metal Ions Negative Ions SCC Science Dept

Introduction Anions are negative ions. Called anions because they are attracted to the anode during electrolysis. Some are simple ions e.g. Cl-, I-,Br-,S2-, N3- Others are complex ions or radicals e.g. SO42-, NO3-, CO32-, HCO3-, SCC Science Dept

Introduction continued Very often asked to distinguish between two similar pairs. SO42- / SO32- - sulphate / sulphite CO32- / HCO32- carbonate / hydrogencarbonate Cl- / Br- - Chloride / Bromide SCC Science Dept

Basic Procedure What to add? What you see happening? Equation. What does this tell you? Sometimes What else you add? What happens? SCC Science Dept

Chloride Cl- Place a little of the suspected chloride in a test tube and add some water. Add some acidified silver nitrate solution (Silver nitrate plus nitric acid) If the substance is a chloride then a white precipitate of silver chloride will form. This precipitate will turn purple and then black in sunlight AgNO3 (aq) + NaCl(aq) = AgCl (s) + NaNO3 (aq) SCC Science Dept

Iodide I- Place a little of the suspected Iodide in a test tube and add some water. Add some acidified silver nitrate solution (Silver nitrate plus nitric acid) If the substance is an iodide then a yellow precipitate of silver iodide will form. AgNO3 (aq) + NaI(aq) = AgI (s) + NaNO3 (aq) SCC Science Dept

Na2SO4 (aq) + BaCl2 (aq) = BaSO4 (s) + 2 NaCl (aq) Sulphate SO42- Place a little of the suspected sulphate in a test tube and add some water Add some barium chloride solution. A white precipitate of Barium sulphate will form if it is a sulphate Na2SO4 (aq) + BaCl2 (aq) = BaSO4 (s) + 2 NaCl (aq) Add some hydrochloric acid [HCl (aq)] to the precipitate it will not re-dissolve SCC Science Dept

Na2SO3 (aq) + BaCl2 (aq) = BaSO3 (s) + 2 NaCl (aq) Sulphite SO32- Place a little of the suspected sulphite in a test tube and add some water Add some barium chloride solution. A white precipitate of Barium sulphite will form if it is a sulphite Na2SO3 (aq) + BaCl2 (aq) = BaSO3 (s) + 2 NaCl (aq) Add some Hydrochloric acid [HCl (aq)] to the precipitate and it will re-dissolve BaSO3(s) + 2HCl(aq) = BaCl2(aq) + SO2(g)+ H2O(l) SCC Science Dept

Carbonate CO32- Hydrogencarbonate HCO31- Place a little of the suspected Carbonate in a test tube and add some dilute HCl (aq) If a gas is produced test it with lime water. If the lime water turns milky the gas is CO2 This tells us that the substance is either a carbonate or a hydrogencarbonate [If it is insoluble in water it is a carbonate.] SCC Science Dept

Carbonate CO32- Hydrogencarbonate HCO31- If soluble take a fresh sample dissolve it in water and add magnesium sulphate solution. If a white precipitate forms then it is a carbonate If no precipitate forms it is a hydrogencarbonate SCC Science Dept

Nitrate NO3- Brown Ring Test Take a sample of the suspected nitrate and place it in a test tube Dissolve it in water if it does not dissolve it is not a nitrate because all nitrates are soluble in water Add some iron(II)sulphate solution SCC Science Dept

Hold the test tube at 45o and gently pour some concentrated sulphuric acid down the side The sulphuric acid is more dense than the water and so will sink to the bottom forming two layers. If the substance is a nitrate a brown ring will form between the two layers. SCC Science Dept