3.2.3-Group 7 Halogens

Question 1

Trends in boiling point down group 7

Answer 1

Increases down group
Increased size makes the van der waals forces increase
More energy required to separate molecules

Question 2

Trends in electronegativity down group 7

Answer 2

Decreases down group
Increased nuclear charge because more protons but
Increasing number of shells therefore more shielding
Increasing atomic radius therefore attraction drops as distance increases

Question 3

Atomic size down group 7

Answer 3

Increases down group

Question 4

Ionic size down group 7

Answer 4

Increases down group
Greater atomic number the more electrons there are which go into shells further away
Ions are larger than atoms due to repulsion from added electrons

Question 5

Oxidising power of group 7 down group

Answer 5

Halogens are oxidising agents 
Weaker down the group
Nucleus attraction affected by
Increased nuclear charge is offset by
Increased shielding 
Increased atomic radius

Question 6

What does chlorine oxidise

Answer 6

Bromide ion to bromine

Iodide ions to iodine

Question 7

What does bromine oxidise

Answer 7

Iodide ions to iodine

Question 8

What does fluorine do as an oxidising agent

Answer 8

Has small size and high electronegativity
So
Brings out highest oxidation energies

Question 9

Stronger to weakest oxidising agents in group 7

Answer 9

Cl2 Strongest
Br2
I2 Weakest

Question 10

Why does oxidising agent down group 7 get weaker

Answer 10

When a halogen acts as an oxidising agent it gains an electrons and is reduced
Down group becomes harder because atoms are larger and experience more shielding

Question 11

What is the order of reducing power in group 7

Answer 11

Strongest I-
Br-
Cl-
Weakest F-

Question 12

Explain the trend in reducing power of halide ions

Answer 12

When a halide ion acts as a reducing agent it loses electrons given to reduced species
Down group it becomes easier to loads an electron because ions are larger and their is more shielding.

Question 13

Halide ions tests

Answer 13

Add nitric acid to remove any other ions

Add silver nitrate produces a precipitate for Cl-, Br-, I-

Add ammonia (dilute and conc) used to see if precipitate redissolves to help confirm identity

Question 14

What will F - show in the halide ion tests and why

Answer 14

No visible change

Silver fluoride is soluble in water

Question 15

What does Cl- produce with a halide ion tests

Answer 15

White precipitate
Ag+ + Cl- –> AgCl

Predicate dissolves in dilute ammonia

Question 16

What does Br- produce in halide ion tests

Answer 16

Cream precipitate produced
Ag+ + Br- –> AgBr(s)

Doesn’t dissolve with dilute NH3
Does dissolve in concentrated NH3

Question 17

What does I- show produce halide ion tests

Answer 17

Yellow precipitate
Ag+ + I- –> AgI (s)
Insoluble in dilute NH3
Insoluble in concentrated NH3

Question 18

Uses of silver salts

Answer 18

[Ag(NH3)2] +
Tollebs reagent tests for aldehydes

[Ag(CN)2] 2-
Silver plating

[Ag(S2O3)2]3-
Photographic fixer

Question 19

Reaction of chlorine with water

Answer 19

Cl2(g) + H2O(l) = HCl(aq) + HOCl (aq)

Question 20

Reaction of chlorine with water in sunlight

Answer 20

2Cl2 +2H2O –> 4HCl + O2

Question 21

What happens to litmus paper in chlorine water

Answer 21

Red due to acidity of HCl

Bleached white by oxidising power of HOCl

Question 22

Equation for manufacture of bleach

Answer 22

2NaOH(aq) + Cl2(g) -> NaCl + NaOCl+H2O

Question 23

Uses of chlorine

Answer 23

Water purification
Bleach 
Solvents 
Polymers 
CFC's

Question 24

Uses of fluorine

Answer 24

CFC

Polymers

Question 25

Uses of Fluoride

Answer 25

Helps prevent tooth decay

Question 26

What does water purification do

Answer 26

Prevents spread of water born diseases e.g. Cholera, typhoid, dysentery

Question 27

Argument against water purification

Answer 27

React with organic matter to form thhalomethanes are linked to with cancer

Taste factor

Quantity of substance influences toxicity