🧪 | Unit 12 | Experimental techniques and chemical analysis

Question 1

A substance is held into the flame of a Bunsen burner using a wire. The flame turns red.

What is the substance?

Answer 1

Lithium ❤️

Question 2

A substance is held into the flame of a Bunsen burner using a wire. The flame turns yellow.

What is the substance?

Answer 2

Sodium 💛

Question 3

A substance is held into the flame of a Bunsen burner using a wire. The flame turns purple.

What is the substance?

Answer 3

Potassium 💜

Question 4

A substance is held into the flame of a Bunsen burner using a wire. The flame turns orange-red.

What is the substance?

Answer 4

Calcium 🧡

Question 5

A substance is held into the flame of a Bunsen burner using a wire. The flame turns blue-green.

What is the substance?

Answer 5

Copper (II) 💚

Question 6

What is the precipitate left behind on addition of NaOH to a metal cation?

Answer 6

The metal hydroxide

Question 7

NaOH is added to a substance. A green precipitate is formed. In excess, it dissolves into a dark green solution.

In aqueous ammonia, a grey-green precipitate is formed which is insoluble in excess.

What is the substance?

Answer 7

Chromium (III)

Question 8

NaOH is added to a substance. A green precipitate is formed. When NaOH is added in excess, the precipitate remains insoluble.

What is the substance?

Answer 8

Iron (II)

Question 9

NaOH is added to a substance. A light blue precipitate is formed. When NaOH is added in excess, the precipitate remains insoluble.

What is the substance?

Answer 9

Copper (II)

Question 10

A red-brown precipitate is formed when a substance reacts with either aqueous ammonia or NaOH. When NaOH/ammonia is added in excess, the precipitate remains insoluble.

What is the substance?

Answer 10

Iron (III)

Question 11

NaOH is added to a substance. A white precipitate is formed. When NaOH is added in excess, the precipitate dissolves to form a colourless solution.

When NH₃ is added to the substance, a white precipitate is formed. When NH₃ is added in excess, the precipitate remains insoluble.

What is the substance?

Answer 11

Aluminium

Question 12

NaOH is added to a substance. A white precipitate is formed. When NaOH is added in excess, the precipitate dissolves to form a colourless solution.

When NH₃ is added to the substance, a white precipitate is formed. When NH₃ is added in excess, the precipitate dissolves to form a colourless solution.

What is the substance?

Answer 12

Zinc

Question 13

NaOH is added to a substance. A white precipitate is formed. When NaOH is added in excess, the precipitate remains insoluble.

What is the substance?

Answer 13

Calcium

Question 14

NaOH is added to a substance. When it is warmed gently, ammonia is produced.

What is the substance?

Answer 14

Ammonium

Question 15

Tests for Aluminium

Answer 15

• NaOH: white precipitate formed, dissolves in excess to form a colourless solution
• NH₃: white precipitate formed, insoluble in excess

Question 16

Tests for Zinc

Answer 16

• NaOH: white precipitate formed, dissolves in excess to form a colourless solution
• NH₃: white precipitate formed, dissolves in excess to form a colourless solution

Question 17

Tests for Calcium

Answer 17

• NaOH: white precipitate formed, insoluble in excess
• NH₃: no visible change, or a faintly visible white precipitate
• Flame test: orange-red flame

Question 18

Tests for Chromium (III)

Answer 18

• NaOH: green precipitate formed, dissolves in excess to form a green solution
• NH₃: grey-green precipitate, insoluble in excess

Question 19

Tests for Copper (II)

Answer 19

• NaOH: light blue precipitate formed, insoluble in excess
• NH₃: light blue precipitate formed, dissolves in excess to form a dark blue solution
• Flame test: blue-green flame

Question 20

Test for Ammonium

Answer 20

• NaOH: Ammonia given off when warmed gently

Question 21

Tests for Iron (II)

Answer 21

• NaOH: green precipitate formed, insoluble in excess
• NH₃: green precipitate formed, insoluble in excess

Question 22

Tests for Iron (III)

Answer 22

• NaOH: red-brown precipitate formed, insoluble in excess
• NH₃: red-brown precipitate formed, insoluble in excess

Question 23

Test for CO₂

Answer 23

Bubbling through limewater
Positive obv: limewater turns milky

Question 24

Test for O₂

Answer 24

Glowing splint test
Positive obv: splint relights

Question 25

Test for H₂

Answer 25

Lighted splint test Positive obv: a "squeaky pop" sound

Question 26

Test for Ammonia

Answer 26

Warm aqueous ammonium in a test tube and place a damp red litmus paper above the solution. Positive obv: red litmus paper turns blue

Question 27

Test for SO₂

Answer 27

Add to acidified potassium (vii) manganate Positive obv: purple to colourless

Question 28

Solubility of Ethanoates

Answer 28

All are soluble

Question 29

Solubility of Nitrates

Answer 29

All are soluble

Question 30

All salts of sodium, potassium and ammonium

Answer 30

All are soluble

Question 31

Solubility of Chlorides

Answer 31

All are soluble except - silver chloride - lead (II) chloride

Question 32

Solubility of Sulfates

Answer 32

All are soluble except - barium sulfate - lead (II) sulfate - calcium sulfate

Question 33

Solubility of Carbonates

Answer 33

All are insoluble except - sodium carbonate - potassium carbonate - ammonium carbonate

Question 34

Solubility of Hydroxides

Answer 34

All are insoluble except - sodium hydroxide - potassium hydroxide - calcium hydroxide (slightly)

Question 35

Difference between a strong acid and a weak acid?

Answer 35

Strong acids ionize completely Weak acids ionize partially

Question 36

Difference between a strong base and a weak base?

Answer 36

Strong bases are soluble Weak bases are not very soluble

Question 37

Test for carbonate

Answer 37

Adding dilute acid will produce CO₂

Question 38

Test for nitrate

Answer 38

Add aqueous NaOH and aluminium foil, and warm gently. Ammonia will be produced.

Question 39

Characteristics of ammonia

Answer 39

Pungent smell, turns damp red litmus paper blue

Question 40

Test for sulfite

Answer 40

Add a dilute acid and warm gently. The gas produced will decolourise acidified aqueous potassium (VII) manganate solution