1. Non-metal Ions Negative Ions
Identifying Anions
Non-metal Ions
Negative Ions
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2. 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-,
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3. Introduction continued
Very often asked to distinguish between two similar pairs.
SO42- / SO sulphate / sulphite
CO32- / HCO32- carbonate / hydrogencarbonate
Cl- / Br Chloride / Bromide
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4. Basic Procedure What to add? What you see happening? Equation.
What does this tell you?
Sometimes
What else you add?
What happens?
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5. 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)
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6. 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)
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7. 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
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8. 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)
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9. 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.]
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10. 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
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11. 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
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12. 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.
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