tests for ions

Question 1

What is the test for chloride ions? (2)

Answer 1

Add silver nitrate solution

Positive result: White precipitate

Question 2

What is the ionic equation for the chloride ion test? (1)

Answer 2

Ag⁺ (aq) + Cl⁻ (aq) → AgCl (s)

Question 3

What is the test for bromide ions? (2)

Answer 3

Add silver nitrate solution

Positive result: Cream precipitate

Question 4

What is the ionic equation for the bromide ion test? (1)

Answer 4

Ag⁺ (aq) + Br⁻ (aq) → AgBr (s)

Question 5

What is the test for iodide ions? (2)

Answer 5

Add silver nitrate solution

Positive result: Yellow precipitate

Question 6

What is the ionic equation for the iodide ion test? (1)

Answer 6

Ag⁺ (aq) + I⁻ (aq) → AgI (s)

Question 7

How can the chloride ion test be verified with ammonia solution? (1)

Answer 7

The white precipitate will dissolve in dilute ammonia solution.

Question 8

How can the bromide ion test be verified with ammonia solution? (1)

Answer 8

The cream precipitate will dissolve in concentrated ammonia solution.

Question 9

How can the iodide ion test be verified with ammonia solution? (1)

Answer 9

The yellow precipitate will not dissolve in ammonia.

Question 10

What is the test for carbonate ions? (4)

Answer 10

Add dilute nitric acid.

Collect any gas formed and pass it through limewater.

Positive result: Fizzing and a colourless gas produced.

Gas turns limewater cloudy.

Question 11

What is the ionic equation for the carbonate ion test? (1)

Answer 11

CO₃²⁻ (aq) + 2H⁺ (aq) → H₂O (aq) + CO₂ (g)

Question 12

What is the test for sulfate ions? (3)

Answer 12

Add an aqueous source of barium ions, eg Ba(NO3)2 (aq)

Positive result: White precipitate formed

Question 13

What is the ionic equation for the sulfate ion test? (1)

Answer 13

Ba²⁺ (aq) + SO₄²⁻ (aq) → BaSO₄ (s)

Question 14

Why can HCl be required in the sulfate ion test? (2)

Answer 14

HCl will react with and remove any carbonates which may be present

carbonates would also produce a precipitate and cause a false positive.

Question 15

What order should the qualitative ion tests be carried out in to avoid false positives? (3)

Answer 15

1. Carbonates test
2. Sulfates test
3. Halides test

Question 16

What is the test for ammonium ions? (3)

Answer 16

Add sodium hydroxide and warm gently.

Test any gas formed with red litmus paper.

Positive result: Red litmus paper turns blue.

Question 17

What is the ionic equation for the ammonium ion test? (1)

Answer 17

NH₄⁺ (aq) + OH⁻ (aq) → NH₃ (aq) + H₂O (aq)