Group 7

Question 1

What are the uses of halogens?

Answer 1

Water purification
Bleaching agents
Flame-retardants
Fire extinguishers
Antiseptic & disinfectant agents

Question 2

What colour is fluorine?

Answer 2

Pale yellow gas

Question 3

What colour is chlorine?

Answer 3

Green/yellow gas

Question 4

What colour is bromine?

Answer 4

Orange/brown liquid

Question 5

What colour is iodine?

Answer 5

Grey/black solid
Purple vapour

Question 6

What does volatility refer to?

Answer 6

How easily a substance can evaporate

Question 7

How does boiling point trend down group 7?

Answer 7

Increases

Question 8

How does volatility trend down group 7?

Answer 8

Decreases

Question 9

What are halogens in terms of bonding?

Answer 9

Diatomic molecules
Covalent bonds formed by overlapping orbitals

Question 10

How are molecules held together by covalent bonding?

Answer 10

Bonding pair of electrons attracted to both nuclei

Question 11

How does atomic size trend down group 7?

Answer 11

Increases

Question 12

How does bond strength trend down group 7?

Answer 12

Decreases

Question 13

Describe the structure and forces present in halogens.

Answer 13

Simple molecular structure
Weak van der Waals forces between diatomic molecules caused by instantaneous dipole-induced dipole forces

Question 14

How do van der Waals forces change down group 7?

Answer 14

Increase as larger molecules and more electrons

Question 15

Why does boiling point increase down group 7?

Answer 15

Van der Waals forces increase

Question 16

How do halogens react with metals?

Answer 16

Accept electron from metal atom to become ion with - charge

Question 17

Describe oxidation/reduction taking place when metal reacts with halogen.

Answer 17

Halogens act as oxidising agents
Halogens oxidise metal by removing electron
Halogens become reduced as they gain electron from metal atom

Question 18

What trend is seen in oxidising power going down group 7?

Answer 18

Decreases

Question 19

What does electronegativity refer to?

Answer 19

How strongly an atom attracts electrons towards itself in a covalent bond

Question 20

What trend is seen in electronegativity going down group 7?

Answer 20

Decreases

Question 21

Why does electronegativity decrease going down group 7?

Answer 21

Atom radius increases
Ability to accept electron decreases due to weaker attraction

Question 22

How is the reactivity of halogens shown?

Answer 22

Displacement reactions with other halide ions in solution

Question 23

What is a displacement reaction?

Answer 23

More reactive element displace less reactive from solution

Question 24

What trend is seen in the reducing power of halide ions going down the group?

Answer 24

Increases

Question 25

Why does the reducing power of halide ions increase down the group?

Answer 25

Ionic radius increases More shielding Outer electrons less attracted to positive nucleus Electrons lost more easily

Question 26

How can halide ions be indentified in an unknown solution?

Answer 26

By dissolving solution in nitric acid and adding silver nitrate solution dropwise

Question 27

Why is nitric acid used when identifying halide ions in solution?

Answer 27

Prevent false positive results from carbonate ions precipitating out with silver ions

Question 28

What is the equation for the reaction between halide ions and silver nitrate solution?

Answer 28

Ag+(aq) + X-(aq) → AgX(s)

Question 29

What colour is silver chloride?

Answer 29

White precipitate

Question 30

What colour is silver bromide?

Answer 30

Cream precipitate

Question 31

What colour is silver iodide?

Answer 31

Yellow precipitate

Question 32

Why is ammonia used as a follow up test for halide ions?

Answer 32

Precipitates close in colour Subjective results

Question 33

How is ammonia used to identify halide ions?

Answer 33

Dilute ammonia added followed by concentrated ammonia

Question 34

What halide ion is present if the precipitate dissolves in dilute ammonia?

Answer 34

Chloride

Question 35

What halide ion is present if the precipitate dissolves in concentrated ammonia but not dilute?

Answer 35

Bromide

Question 36

What halide ion is present if the precipitate dissolves in neither dilute or concentrated ammonia?

Answer 36

Iodide

Question 37

Why are reactions between halide ions and concentrated sulfuric acid done in fume cupboard?

Answer 37

Produce toxic gases

Question 38

What is the general reaction of halide ions with concentrated sulfuric acid?

Answer 38

H₂SO₄(l) + X-(aq) → HX(g) + HSO₄-(aq)

Question 39

What happens in reaction between sodium chloride and concentrated sulfuric acid?

Answer 39

Sulfuric acid added dropwise to sodium chloride crystals to produce hydrogen chloride gas HCl gas seen as white fumes

Question 40

What is the equation for the reaction between sodium chloride and concentrated sulfuric acid?

Answer 40

H₂SO₄ (l) + NaCl (s) → HCl (g) + NaHSO₄ (s)

Question 41

What happens in reaction between sodium bromide and concentrated sulfuric acid?

Answer 41

Sulfuric acid oxidises HBr which decomposes into bromine and hydrogen gas Sulfuric acid reduced to sulfur dioxide gas Bromine seen as reddish-brown gas

Question 42

What is the equation for the reaction between sodium bromide and concentrated sulfuric acid?

Answer 42

H₂SO₄ (l) + NaCl (s) → HCl (g) + NaHSO₄ (s)

Question 43

What is the equation for the reaction between sodium iodide and concentrated sulfuric acid?

Answer 43

H₂SO₄ (l) + NaI (s) → HI (g) + NaHSO₄ (s)

Question 44

What happens after reaction between sodium iodide and concentrated sulfuric acid?

Answer 44

Hydrogen iodide decomposes readily Sulfuric acid oxidises hydrogen iodide and reduces to sulfur dioxide gas

Question 45

What is the equation for the reaction between hydrogen iodide and concentrated sulfuric acid?

Answer 45

2HI (g) + H₂SO₄ (l) → I₂ (g) + SO₂ (g) + 2H₂O (l)

Question 46

What happens after reaction between hydrogen iodide and concentrated sulfuric acid?

Answer 46

Sulfuric acid oxidises HI and is reduced to sulfur

Question 47

What is the equation for the reaction between hydrogen iodide and concentrated sulfuric acid?

Answer 47

8HI (g) + H₂SO₄ (l) → 4I₂ (g) + H₂S (s) + 4H₂O (l)

Question 48

What are the observations for products at each stage when sodium iodide reacts with sulfuric acid?

Answer 48

Iodine is purple vapour Sulfur is yellow solid Hydrogen sulfide has strong smell of bag eggs

Question 49

What is a disproportionation reaction?

Answer 49

A reation in which the same species is both oxidised and reduced

Question 50

What is chlorine commonly used as?

Answer 50

Sterilising agent in drinking water and pools

Question 51

What is the equation for the reaction of chlorine in sunlight?

Answer 51

2Cl₂ (g) + 2H₂O (l) → 4HCl (aq) + O₂ (g)

Question 52

What is the equation for chloric acid dissociating in water?

Answer 52

HClO (aq) → H+ (aq) + ClO- (aq)