3. Group 7

Question 1

Reducing Strength of Halides:

Answer 1

• increases down the group
• shielding increases
• weaker attraction between nucleus and outer e-

Question 2

Observation for SO2(g)

Answer 2

Acidic gas

Question 3

Observation for S(s)

Answer 3

yellow precipitate

Question 4

Observation for H2S(g)

Answer 4

bad egg smell

Question 5

Reduction Half Equation for SO2 from H2SO4

Answer 5

2e- + 2H+ + H2SO4 → SO2 + H2O

Question 6

Reduction Half Equation for S from H2SO4

Answer 6

6e- + 6H+ + H2SO4 → S + 4H2O

Question 7

Reduction Half Equation for H2S from H2SO4

Answer 7

8e- + 8H+ + H2SO4 → H2S + 4H2O

Question 8

Reducing Agent for Reduction of H2SO4 to SO2

Answer 8

Br-, I-

Question 9

Reducing Agent for Reduction H2SO4 to S

Answer 9

I-

Question 10

Reducing Agent for Reduction of H2SO4 to H2S

Answer 10

I-

Question 11

Role of H2SO4 in the Reduction of H2SO4 to SO2/S/S/H2S

Answer 11

oxidising agent

Question 12

Acid-Based Reaction

Reaction of H2SO4 with NaF

Answer 12

H2SO4 + NaF → NaHSO4 + HF
(simplest: H+ + F- → HF)

Question 13

Reaction of H2SO4 with NaCl

Answer 13

H2SO4 + NaF → NaHSO4 + HCl
(simplest: H+ + F- → HCl)

Question 14

What is H2SO4 acting as in its reaction with NaF and Cl-?

Answer 14

an acid

Question 15

What are Cl- and F- acting as in their reactions with H2SO4?

Answer 15

a base

Question 16

Oxidation half equation for the production of I2

Answer 16

2I- → I2 + 2e-

Question 17

Oxidation half equation for the production of Br2

Answer 17

2Br- → Br2 + 2e-

Question 18

Test for Halides

Answer 18

AgNO3

Question 19

Observations for Halide Tests when only AgNO3 has been added

Answer 19

AgCl(s) = white ppt
AgBr(s) = cream ppt
AgI(s) = yellow ppt

Question 20

Equations for Halide Tests when only AgNO3 has been added

Answer 20

Ag+ (aq) + Cl- (aq) → AgCl (s)
Ag+ (aq) + Br- (aq) → AgBr (s)
Ag+ (aq) + I- (aq) → AgI (s)

Question 21

Why do you add HNO3 before AGNO3 when testing for halides?

Answer 21

to remove any possible carbonate impurities which would result in a false positive

Question 22

To further differentiate between the samples, what should you add?

Answer 22

Dilute and concentrated NH3

Question 23

Equation for halide test when dilute NH3 has been added to AgCl(s)

Answer 23

AgCl (s) + 2NH3 → [Ag(NH3)2]+ (aq) + Cl-

Question 24

Equation For Halide Test when Dilute has been added to AgBr(s)

Answer 24

AgBr (s) + 2NH3 → [Ag(NH3)2]+ (aq) + Br-

Question 25

Oxidising Ability of Halogens

Answer 25

- larger radius - weaker attraction between nucleus and incoming e- - decreases down the group

Question 26

A [more/less] reactive halogen ( [stronger/weaker] oxidising agent) will displace a [more/less] reactive halogen ( [stronger/weaker] oxidising agent)

Answer 26

1. more reactive 2. stronger 3. less reactive 4. weaker

Question 27

Complete and state the observation Cl2 + 2NaBr → | Cl2 + 2Br- →

Answer 27

Br2 + 2NaCl observation = orange solution (Br2) | Br2 + 2Cl-

Question 28

Complete and state the observation Cl2 + 2NaI → | Cl2 + 2I- →

Answer 28

I2 + 2NaCl observation = brown solution/black solid (I2) | I2 + 2Cl-

Question 29

Complete and state the observation Br2 + 2NaI → | Br2 + 2I- →

Answer 29

I2 + 2NaBr observation = brown solution/black solid (I2) | I2 + 2Cl-

Question 30

Use of Chlorine

Answer 30

kills bacteria

Question 31

Why is chlorine used in low concs?

Answer 31

as its toxic

Question 32

Disproportionation reaction for Cl2 with H2O

Answer 32

Cl2 + H2O ⇌ HCl + HClO | Cl2 reduced to HCl (0 to -1) Cl2 oxidised to HClO (0 to +1)

Question 33

Equation for the production of bleach (NaClO)

Answer 33

Cl2 + 2NaOH → NaCl + NaClO + H2O | NaOH = cold, dilute and aqueous