✅ 7. Required Practical: Identifying Ions (C12)

Question 1

Aim of this Practical

Answer 1

You are going to identify some ionic compounds by testing to identify both the positive and negative ions.

Question 2

Health and Safety Measures

Answer 2

(-Symbols Associate show there are:

• Oxidising Agents
• Caution/Harmful
• Corrosive Substances
• Wear Safety Goggles)
• Treat all the compounds as corrosive, harmful, irritant and oxidising.
• Ensure you stopper the test tube when shaking to dissolve and keep your thumb on the bung.

Question 3

How do you carry out flame tests for positive ions

Answer 3

Place a damp splint into some of the ionic compound as a solid. Then place the splint in a roaring Bunsen flame and look for any colour.

Question 4

How do you carry out the sodium hydroxide test for positive ions

Answer 4

Dissolve a small amount of the solid ionic compound in deionised water (about 3 cm depth). Then add sodium hydroxide solution. If a white precipitate forms, test it further by adding more sodium hydroxide solution.

Question 5

How do you carry out halide ion tests for negative ions

Answer 5

Dissolve a small amount of the solid ionic compound in deionised water (about 3 cm depth). Then add a few drops of nitric acid followed by 1 cm depth of silver nitrate solution.

Question 6

How do you carry out the sulphate ion test for negative ions

Answer 6

Dissolve a small amount of the solid ionic compound in deionised water (about 3 cm depth). Then add a few drops of hydrochloric acid followed by 1cm depth of barium chloride solution.

Question 7

How do you carry out the carbonate ion test for negative ions

Answer 7

Place some hydrochloric acid in a test tube and add a small spatula load of the solid ionic compound. Look for bubbles of gas. If a gas is released then insert a delivery tube into the test tube and bubble the gas through limewater.

Question 8

What result and test can show positive for Lithium, Li^+ ions

Answer 8

A crimson (red) flame from the flame test

Question 9

What result and test can show positive for Sodium, Na^+ ions

Answer 9

A yellow flame from the flame test

Question 10

What result and test can show positive for Potassium, K^+ ions

Answer 10

A lilac (purple) flame from the flame test

Question 11

What result and test can show positive for Copper, Cu^2+ ions

(+Ionic Equation for the reaction)

Answer 11

A green flame from the flame test

OR

Blue precipitate from adding sodium hydroxide (aq)
Cu^2+ (aq) + 2OH^- (aq) —> Cu(OH)2 (s)

Question 12

What result and test can show positive for Calcium, Ca^2+ ions

(+Ionic Equation for the reaction)

Answer 12

An orange-red flame from the flame test

OR

White precipitate (does not dissolve when more NaOH added) from adding Sodium Hydroxide

Ca^2+ (aq) + 2OH^- (aq) —> Ca(OH)2 (s)

Question 13

What result and test can show positive for Magnesium, Mg^2+ ions

(+Ionic Equation for the reaction)

Answer 13

White precipitate (does not dissolve when more NaOH added) from adding Sodium Hydroxide

Mg2+ (aq) + 2OH– (aq) → Mg(OH)2 (s)

Question 14

What result and test can show positive for Aluminium, Al^3+ ions

(+Ionic Equation for the reaction)

Answer 14

White precipitate (dissolves when more NaOH added) from adding Sodium Hydroxide

Al3+ (aq) + 3OH– (aq) → Al(OH)3 (s)

Question 15

What result and test can show positive for Iron (II), Fe^2+ ions

(+Ionic Equation for the reaction)

Answer 15

Green precipitate is formed from adding Sodium Hydroxide

Fe2+ (aq) + 2OH– (aq) → Fe(OH)2 (s)

Question 16

What result and test can show positive for Iron (III), Fe^3+ ions

(+Ionic Equation for the reaction)

Answer 16

Brown precipitate is formed from adding Sodium Hydroxide

Fe3+ (aq) + 3OH– (aq) → Fe(OH)3 (s)

Question 17

What results and tests can show positive for Carbonate, CO3^2- ions

Answer 17

Bubbles of gas (that turn limewater cloudy) after adding dilute acid

(would form bubbles of gas when acid added) when barium chloride (aq) with hydrochloric acid are added

(would form bubbles of gas when acid added) when silver nitrate (aq) with nitric acid are added

Question 18

What result and test can show positive for Sulphate, SO4^2- ions

(+Ionic Equation for the reaction)

Answer 18

White precipitate is formed after barium chloride (aq) with hydrochloric acid is added

Ba2+ (aq) + SO42– (aq) → BaSO4 (s)

Question 19

What result and test can show positive for Chloride, Cl- ions

(+Ionic Equation for the reaction)

Answer 19

White precipitate is formed after silver nitrate (aq) with nitric acid is added

Ag+ (aq) + Cl– (aq) → AgCl (s)

Question 20

What result and test can show positive for Bromide, Br- ions

+Ionic Equation for the reaction

Answer 20

Cream precipitate is formed after silver nitrate (aq) with nitric acid is added

Ag+ (aq) + Br– (aq) → AgBr (s)

Question 21

What result and test can show positive for Iodide, I- ions

+Ionic Equation for the reaction

Answer 21

Yellow precipitate is formed after silver nitrate (aq) with nitric acid is added

Ag+ (aq) + I– (aq) → AgI (s)

Question 22

Plan a sequence of chemical tests that would distinguish these four compounds. Describe the results that you would expect.

• Sodium Sulfate
• Sodium Carbonate
• Sodium Iodide
• Potassium Iodide

Answer 22

Test 1:
Place a damp splint into some of the ionic compound as a solid. Then place the splint in a roaring Bunsen flame and look for a colour. If sodium is present, it will burn a yellow flame, and is potassium is present, then there will be a lilac flame.

If there is a lilac flame, then that compound is the potassium iodide.

Test 2:
Dissolve a small amount of the solid ionic compound in deionised water (about 3 cm depth). Then add a few drops of nitric acid followed by 1 cm depth of silver nitrate solution. A chloride will give a white precipitate, a bromide will give a cream precipitate, and an iodide will give a yellow precipitate.

If there is a yellow precipitate, then the compound is sodium iodide.

Test 3:
Dissolve a small amount of the solid ionic compound in deionised water (about 3 cm depth). Then add a few drops of hydrochloric acid followed by 1cm depth of barium chloride solution. If sulphate ions are present, a white precipitate will form.

If there is a white precipitate, then the compound is sodium sulphate.

Test 4:
Place some hydrochloric acid in a test tube and add a small spatula load of the solid ionic compound. Look for bubbles of gas. If a gas is released then insert a delivery tube into the test tube and bubble the gas through limewater. If the carbonate ions are present, then the limewater turns couldy when it bubbles pass through it.

If the limewater turns cloudy when bubbles pass through it, then the compound is sodium carbonate.

Question 23

Write an ionic equation including state symbols for each of the following precipitation reaction:

A yellow precipitate is formed when silver nitrate solution is added to a solution of sodium iodide

Answer 23

Ag^+ (aq) + I^- (aq) —> AgI (s)

Question 24

Write an ionic equation including state symbols for each of the following precipitation reaction:

A white precipitate is formed when barium chloride solution is added to a solution of potassium sulfate

Answer 24

Ba^2+ (aq) + SO4^2- (aq) —> BaSO4 (s)

Question 25

Write an ionic equation including state symbols for each of the following precipitation reaction:

A white precipitate is formed when sodium hydroxide solution is added to a solution of calcium nitrate

Answer 25

Ca^2+ (aq) + 2OH^- (aq) —> Ca(OH)2 (s)