8.2 The Halogens

Question 1

What group is the halogens?

Answer 1

Group 7

Question 2

How do halogens exist on earth?

Answer 2

As stable halide ions (Cl-, Br-, I-) dissolved in sea water
Combined with sodium or potassium as solid deposits (NaCl)

Question 3

At room temperature and pressure (RTP), how do halogens exist?

Answer 3

As diatomic molecules (X2)

Question 4

What is the change of group 7 elements?

Answer 4

-1

Question 5

What is the trend in bioling points down group 7 (halogens)?

Answer 5

Boiling point increases

Question 6

Explain the trend in boiling point down group 7 (the halogens)?

Answer 6

More electrons
Stronger London forces
More energy required to break the intermolecular forces
So boiling point increases as you go down the group

Question 7

What is the structure of halogens in their solid state?

Answer 7

Simple molecular lattices

Question 8

How many electrons are in the outer shell of halogens?

Answer 8

7

Question 9

What is the outer shell configuration of halogens?

Answer 9

s2p5

Question 10

When undergoing a redox reaction, what happens to a halogen?

Answer 10

Halogen is reduced, gaining one electron to form a 1- halide ion

Question 11

What is the half equation for chlorine being reduced?

Answer 11

Cl2 + 2e- → 2Cl-

Question 12

Why are halogens oxidising agents?

Answer 12

As another species loses electrons to halogen toms. Halogens have oxidised another species

Question 13

Definition of oxidising agent

Answer 13

A reagent that oxidises (takes electrons from) another species

Question 14

What is a disproportionation reaction

Answer 14

A redox reaction in which the same element is both oxidised and reduced

Question 15

What is a displacement reaction?

Answer 15

A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of its ions

Question 16

What is the reactivity of halogens down the group?

Answer 16

Reactivity of halogens decreases down the group

Question 17

What colour of Cl2 solution in water?

Answer 17

pale green

Question 18

What colour of Br2 solution in water?

Answer 18

orange

Question 19

What colour of l2 solution in water?

Answer 19

brown

Question 20

How can you tell apart solutions of Br2 and I2?

Answer 20

Adding an organic non-polar solvent such as cyclohexane and shake the mixture. The non-polar halogens dissolve more readily in cyclohexane so their colours are easier to tell apart

Question 21

What colour of Cl2 solution in cyclohexane?

Answer 21

pale green

Question 22

What colour of Br2 solution in cyclohexane?

Answer 22

orange

Question 23

What colour of l2 solution in cyclohexane?

Answer 23

deep violet

Question 24

What is the displacement reaction between Cl2 and Br-?

Answer 24

Cl2 (aq) + 2Br- (aq) → 2Cl- (aq) + Br2 (aq)

Question 25

What is the equation for the displacement reaction of Cl2 and I-?

Answer 25

Cl2 (aq) + 2I- (aq) → 2Cl - (aq) + I2 (aq)

Question 26

What is the equation for the displacement reaction of Br2 and I-?

Answer 26

Br2 (aq) + 2I- (aq) → 2Br- (aq) + I2 (aq)

Question 27

What can we indicate from the displacement reactions between the halogens?

Answer 27

-Cl2 has reacted with both Br- and I- -Br2 has reacted with only I- -I2 has not reacted at all -This tells us that the reactivity decreases as we go down the halogens

Question 28

What happens in a displacement reaction if the halogen is more reactive than the halide?

Answer 28

-The halogen will displace the halide from the solution -Solution will change colour

Question 29

What colour change is present after the displacement reaction of Cl2 and Br-?

Answer 29

orange

Question 30

What colour change is present after the displacement reaction of Cl2 and I-?

Answer 30

deep violet

Question 31

What colour change is present after the displacement reaction of Br2 and I-?

Answer 31

deep violet

Question 32

What is the reactivity of fluorine like?

Answer 32

Reacts with almost any substance that it comes in contact with

Question 33

What is the reactivity of astatine like?

Answer 33

Rare, as it is radioactive and decays rapidly. least reactive halogen

Question 34

Explain the trend in reactivity down the halogens

Answer 34

Atomic radius increases More inner shells so shielding increases Less nuclear attraction to capture an electron from another species So reactivity decreases

Question 35

Which halogen is the strongest oxidising agent?

Answer 35

Fluorine, gain electrons from other species more readily than other halogens, weaker oxidising agents as you go down the group

Question 36

What is the reaction between chlorine and water?

Answer 36

Cl2 (aq) + H2O (l) → HClO (aq) + HCl (aq)

Question 37

What type of reaction is the reaction between chlorine and water?

Answer 37

Disproportionation

Question 38

What is the reaction between chlorine and cold, dilute aquarius sodium hydroxide?

Answer 38

Disproportionation reaction

Question 39

What are the benefits of chlorine use in water treatment (purification)

Answer 39

Kill bacteria

Question 40

What are the risks of chlorine use in water treatment (purification)

Answer 40

Extremely toxic gas Respiratory irritant in small concentrations, large concentrations can be fatal Can react with organic hydrocarbons to form chlorinated hydrocarbons which are suspected of causing cancer

Question 41

What would happen if we didn’t add chlorine to water?

Answer 41

Quality of drinking would be compromised, diseases such as typhoid and cholera may break out

Question 42

What is the test for halogen atoms?

Answer 42

Add to silver nitrate to form precipitates of silver halides

Question 43

What is the overall equation for the reaction of halides with silver ions?

Answer 43

Ag + (aq) + X- (aq) → AgX (solid)