C9 Group 2 And The Halogens, Qualitative Analysis

Question 1

Disproportionation

Answer 1

Occurs when the same element both increases and decreases its oxidation numbers so that the element is simultaneously oxidised and reduced

Question 2

Physical properties

Answer 2

Good conductors
High melting/ boiling points
Generally colourless ionic compounds except beryllium

Question 3

Trend in reactivity

Answer 3

Reactivity increases down the group

Loose electrons

Question 4

Reaction with oxygen

Answer 4

Form ionic oxides 
Mg- white light 
Ca- brick red flame 
Sr- crimson flame 
Ba- green flame

Question 5

Uses of ionic oxides

Answer 5

MgO- very high melting point so lines furnaces

CaO- ‘quicklime’ reacts rapidly with water to produce calcium hydroxide and is used to reduce acidity in soil

Question 6

Reaction with water

Answer 6

Mg- reacts slowly= white precipitate

With steam forms oxide

Question 7

Reaction with Cl

Answer 7

Form white chlorides

Ionic substance

Question 8

Reaction with dilute acids

Answer 8

Salt and hydrogen gas

Question 9

Reaction is group 2 oxides

Answer 9

React with water- hydroxides

React with acids to form salts

Question 10

Group 2 oxide uses

Answer 10

Mg hydroxide 
Treats indigestion 
Ca Oxide 
Limewater 
Test for CO2

Question 11

Reactions of group 2 carbonates

Answer 11

Form oxides

Carbon dioxide

Question 12

Group 2 sulfates

Answer 12

Solubility decreases down the group

White solids

Question 13

Group 17 physical properties

Answer 13

Poor conductors
Coloured gas
Down group increase in induced dipole-dipole interactions
More electrons down group
Electronegativity decreases down the group
Oxidising agents

Question 14

Group 17 chemical properties

Answer 14

Gain electrons when reacting to form anions
Atomic radius and shielding increases down the group
Form halides

Question 15

Displacement reactions

Group 17

Answer 15

Fl- displaces Cl-, Br- and I-
Cl- displaces Br- and I-
Br- displaces I-
I- Cabot displace any of the above

Question 16

Uses of chlorine

Answer 16

Water treatment
Reacts reversibly with water and the resultant mixture kills bacteria
Redox reaction
Cl2 oxidised 0 to +1
Cl2 reduces 0 to -1
React with sodium hydroxide to form bleach

Question 17

Benefits of water treatment

Answer 17

Kills micro organisms

Reduce diseases

Question 18

Risks of water treatment

Answer 18

Disinfectant is harmful
Bladder and colon cancer can form
Trichloroethane present

Question 19

Testing for Halide ions

Answer 19

Silver chloride-
White precipitation turns grey in sunlight
Silver bromide-
Cream precipitation rapidly darkens in sunlight
Silver iodide-
Yellow precipitation
Colour changes are not distinct so add:
Dilute ammonia- dissolves silver chloride
Concentrated ammonia- dissolve silver bromide, silver iodide doesn’t dissolve in ammonia