Topic 12-Introduction to redox and group 7

Question 1

Rules for oxidation states

Answer 1

In a monatomic atom- its the given charge
Oxygen nearly always -2 except for peroxides where its -1
Hydrogen is nearly always +1 except for hydrides where its -1
Elements always 0

Question 2

Trends in halogens

Answer 2

Boiling point increases down the group- due to increased mass of molecules
Electronegativity decreases down the group- Increased atomic radius and sheilding
Halogens displace less reactive halides

Question 3

Trends in halogens

Answer 3

Boiling point increases down the group- due to increased mass of molecules
Electronegativity decreases down the group- Increased atomic radius and sheilding
Halogens displace less reactive halides

Question 4

Reaction of halogens with potassiumhalide solutions

Answer 4

Chlorine- Will displace bromide and iodide- forming an orange and brown solution respectively
Bromine- Will Displace iodide- forming brown solution only
Iodine will not displace anthing

Question 5

Reaction of chlorine with sodium hydroxide

Answer 5

2NaOH + Cl2 –> NaClO(bleach) + NaCl + H2O

Question 6

Uses of sodium chlorate

Answer 6

• Water treatment
• Bleaching paper and textiles
• Cleaning toilets

Question 7

Reaction of chlorine in water (Type and equation)

Answer 7

Disproportionation
Cl2 + H2O <—–> HCl + HClO

Question 8

Positives of use of chlorine in water

Answer 8

• Kills disease
• Remains in water, preventing reinfection
• Prevents growth of algae
• Removes discolouration caused by organic products

Question 9

Negatives of chlorine treatment

Answer 9

• Chlorine is very harmful- accidents with it could be fatal
• Chlorine can react with hydrocarbons- forming chlorinated hydrocarbons which are carcinogenic

Question 10

Why does the strength of reducing agent increase down a group

Answer 10

• Ions get bigger- electrons are further away from the positive nucleus
• There are extra inner electron shells, so greater sheilding effect

Question 11

Main products in reaction with sulfuric acid (Each halogen)

Answer 11

Fluorine and Chlorine- HF + HCL
Bromine- HBr + SO2
Iodine- HI + SO2 + H2S

Question 12

Why do reducing agents get better as you go down group 7?

Answer 12

Larger atomic radius
More sheilding
Easier to lose an electron

Question 13

Why do oxidising agents get better up a group?

Answer 13

Lower atomic radius
Less sheilding
Charge from nucleus is felt more

Question 14

Testing for halides

Answer 14

• Add dilute nitric acid and silver nitrate

- (F- No precipitate) (Cl- White) (Br- Cream) (I- yellow)

Question 15

Solubility of silver halides in ammonia

Answer 15

Chloride- Dissolves in dilute
Bromide- Dissolves in conc NH3
Iodide- Insoluble even in conc NH3

Question 16

Equations of Chloride with sulfuric acid

Answer 16

NaCl + H2SO4 –> NaHSO4 + HCL

Question 17

Reaction of bromide with Sulfuric acid and observations

Answer 17

NaBr + H2SO4 --> NaHSO4 + HBr 
HBr + H2SO4 --> SO2 + Br2 + H2O
Misty fumes (HBr) 
Choking fumes (SO2)
Brown fumes (Br2)

Question 18

Reaction of iodide with sulfuric acid

Answer 18

NaI + H2SO4 –> HI + NaHSO4
HI + H2SO4 –> SO2 + I2 + H2O
HI + SO2 –> S + I2 + H2O
HI + S —> H2S + I2

Question 19

What is the role of sulfuric acid in reaction with halides

Answer 19

Oxidising agent (In redox reactions only)

Question 20

Reaction of chlorine with water in sunlight

Answer 20

Question 21

Why do iodine compounds react fastest

Answer 21

Because they have the weakest/ lowest bond enthalpy

Question 22

Reaction of bromide ions with sulfuric acid

Answer 22