Cation Testing

Question 1

How can barium (Ba2+) ions be identified?

Answer 1

• Adding sulfate (SO4 2-) ions: white precipitate
• Flame test: pale green

Question 2

How can calcium (Ca2+) ions be identified?

Answer 2

• Adding sulfate (SO4 2-) ions: white precipitate
• Flame test: orange red

Question 3

How can magnesium (Mg2+) ions be identified?

Answer 3

Through elimination (no flame test colour, non specific precipitate)

Question 4

How can lead (II) (Pb2+) ions be identified?

Answer 4

• Adding NaOH (strong base): white precipitate
• Adding iodide ions: yellow precipitate
• Adding chloride ions: white precipitate

Note: Solutions containing Pb2+ should not be tested with flame test as vaporised Pb2+ is a health hazard

Question 5

How can silver (Ag+) ions be identified?

Answer 5

• Adding chloride ions: white precipitate
• Adding bromide ions: cream precipitate
• Adding iodide ions: yellow precipitate
• Adding OH- will produce AgOH which decomposes to form brown Ag2O which is soluble in acid and alkaline solutions

Ag+(aq) + OH-(aq) -> AgOH(s)
2 AgOH(s) -> Ag2O(aq) + H2O(l)

Question 6

How can copper (II) (Cu2+) ions be identified?

Answer 6

• Adding a strong base (NaOH): blue precipitate
• Flame test: green/blue)

Question 7

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How can iron (II) (Fe2+) ions be identified?

Answer 7

• Adding a strong base (NaOH): green precipitate

Question 8

How can iron (III) (Fe3+) ions be identified?

Answer 8

• Adding a strong base (NaOH): brown precipitate