Topic 4

Question 1

Solubility of group 2 hydroxides

Answer 1

Solubility increases down the group

Question 2

Solubility of group 2 sulfates

Answer 2

Solubility decreases down the group

Question 3

Solubility of group 2 carbonates

Answer 3

All insoluble

Question 4

Trend in in thermal stability of group 1/2 carbonates and nitrates

Answer 4

Thermal stability increases down the group.

Number of shells increases, but same number of electrons delocalise per atom so the charge density decreases.
This decreases the polarising power of the cation.
Cation less easily polarises and weakens the covalent bond (C-O or N-O).
Covalent bond is stronger, more thermal energy needed to break bond for thermal decomposition.

Group 1 vs 2
Group 1 has lower charge density, so more thermal stability. Group 1 and 2 decompose with slightly different products.
Exception: Lithium behaves like group 2 because it has a high enough charge density.

Question 5

Reason for flame colours

Answer 5

The ion is excited by heating it strongly and electrons move to a higher energy level.
As the electrons fall back down to lower levels, energy is released as light.
The different distances moved between different shells mean different amounts of energy are released and each corresponds to a particular colour of light.

Question 6

Trend in melting points of halogens

Answer 6

Increase down the group

-london forces

Question 7

Trend in reactivity of halogen molecules and halide ions

Answer 7

Halogen molecules: decrease down the group

Halide ions: increase down the group

Question 8

Test for halides

Answer 8

Nitric acid to remove impurities
Silver nitrate solution
Precipitate formed
Cl- white, dissolves in dilute ammonia
Br- cream, dissolves in conc. ammonia
I- yellow, doesn't dissolve in ammonia

Question 9

Test for sulfates

Answer 9

Hydrochloric acid to remove impurities
Barium chloride solution
Forms barium sulfate (white ppt)

Question 10

Test for carbonates and hydrogencarbonates

Answer 10

Add acid, look for effervencence (CO2)

Question 11

Test for ammonium ions

Answer 11

Dissolve in water
Sodium hydroxide solution (source of OH-)
Warm
Ammonia gas formed
-pungent smell and turns damp red litmus blue

Question 12

Which halide ion is the strongest reducing agent?

Answer 12

Most electrons are gained per atom of sulphur in the reaction with iodide ions, so iodide ions are the strongest reducing agent.

Question 13

How do flame colours arise?

Answer 13

Heating excites electrons to higher energy levels
Electrons fall back to lower energy levels
Emitting light
Moving between different energy levels in different elements means different amounts of energy is emitted, which correspond to different colours of light
If there is no colour, the energy emitted is outside the visible spectrum