Tests for Negative Ions

Question 1

How do you check for Carbon dioxide (CO₂)?

Answer 1

1) You can test if a gas is CO₂ by bubbling it through limewater. If it is CO₂, the limewater turns cloudy
2) You can use this to test fro carbonate ions (CO₃²⁻), since carbonates react with dilute acids to form carbon dioxide

Question 2

Acid + Carbonate ->

Answer 2

Salt + Water + Carbon dioxide

Question 3

How do you test for Chloride (Cl⁻), Bromide (Br⁻) or Iodide (I⁻) ions?

Answer 3

Add dilute nitric acid (HNO₃) followed by silver nitrate (AgNO₃)

Question 4

What colour precipitate does chloride form? What is the equation?

Answer 4

White = silver chloride

Ag⁺ (aq) + Cl⁻ (aq) -> AgCl (s)

Question 5

What colour precipitate does bromide form? What is the equation?

Answer 5

Cream = silver bromide

Ag⁺ (aq) + Br⁻ (aq) -> AgBr (s)

Question 6

What colour precipitate does iodide form? What is the equation?

Answer 6

Yellow = silver iodide

Ag⁺ (aq) + I⁻ (aq) -> AgI (s)

Question 7

How do you test for sulfate ions (SO₄²⁻)?

Answer 7

Add dilute HCl, followed by barium chloride solution (BaCl₂)

Question 8

What does a white precipitate of barium sulfate mean? What is the symbol equation?

Answer 8

The original compound was a sulfate

Ba²⁺ (aq) + SO₄²⁻ (aq) -? BaSO₄ (s)