Tests for ions

Question 1

Give the test for halide ions and the results

Answer 1

Add acidified silver nitrate solution

Cl⁻ → white ppt
Br⁻→ off white / cream ppt
I⁻→ yellow ppt

Question 2

Give the simplest ionic equation for the test of a halide ion: X⁻

(X⁻ is not fluoride)

Answer 2

Ag⁺(aq) + X⁻(aq) → AgX(S)

(AgF would be (aq))

Question 3

Which halide ion produces a white ppt in acidified silver nitrate solution?

Answer 3

Cl⁻

Question 4

Which halide ion produces a cream ppt in acidified silver nitrate solution?

Answer 4

Br⁻

Question 5

Which halide ion produces a yellow ppt in acidified silver nitrate solution?

Answer 5

I⁻

Question 6

Why do fluoride ions not produce a ppt in acidified silver nitrate solution

Answer 6

AgF is soluble

Question 7

Give 2 observations when acidified silver nitrate is added to a solution containing halide ions and carbonate ions

Answer 7

Effervescence / bubbling
(Carbonate ions react with acid to produce CO₂)
Coloured ppt
(Ag⁺ reacts with halide ion)

Question 8

How can ammonia distinguish silver halide precipitates?

Answer 8

AgCl dissolves in some NH₃
AgBr dissolves in excess NH₃
AgI is insoluble in NH₃

Question 9

Why does silver nitrate need to be acidified to test for halide ions?

Answer 9

To prevent the formation of AgCO₃ which is a white solid. (would confuse the results)

Question 10

What is the test for ammonium (NH₄⁺) ions?

Answer 10

Add NaOH solution and warm the mixture. A gas is produced (NH₃) that turns red litmus paper blue (it is basic)

Question 11

Give the simplest ionic equation for the test for ammonium ions

Answer 11

NH₄⁺(aq) + OH⁻(aq) → NH₃(g) + H₂O(l)

Question 12

Give the test for carbonate ions (CO₃²⁻)

Answer 12

Add an acid - bubbles formed.
Bubbling gas through limewater will turn it cloudy, proving the gas produced is CO₂

Question 13

Give the simplest ionic equation for the test for carbonate ions

Answer 13

2H⁺(aq) + CO₃²⁻(aq) → H₂O(l) + CO₂(g)

Question 14

Give the test for hydroxide ions

Answer 14

Add a solution of Mg²⁺ ions. Forms a white ppt of Mg(OH)₂

Question 15

Give the simplest ionic equation for the test for hydroxide ions

Answer 15

Mg²⁺(aq) + 2OH⁻(aq) → Mg(OH)₂(s)

Question 16

Give the test for sulfate ions

Answer 16

Add acidified barium chloride solution. White ppt of BaSO₄ formed

Question 17

Give the simplest ionic equation for the test for sulfate ions

Answer 17

Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)

Question 18

Why does barium chloride need to be acidified in the test for sulfate ions?

Answer 18

To prevent the formation of Ba(CO₃)₂ which is a white solid and could give a false positive

Question 19

Give two sources of aqueous sulfate ions

Answer 19

Solutions of group 1 sulfate salts (eg NaSO₄)
Sulfuric acid

Question 20

How would you prepare an inorganic solid for testing

Answer 20

Dissolve in water (Grind in pestle and mortar first if necessary)