Group 2

Question 1

Atomic radius

Answer 1

• increases down group

* more shells of electrons making the atom bigger

Question 2

1st ionisation energy

Answer 2

• decreases down group
• electron further from nucleus
• outer electrons are more shielded from the nucleus.
• less attraction
• easier to remove

Question 3

Melting points

Answer 3

• decreases down group
• delocalised electrons further from nucleus
• more shielding
• less attraction between ions and delocalised e-

Question 4

Reactivity

Answer 4

• increases down group
• more shielding
• easier to lose electrons forming M2+ ions

Question 5

Reaction with water

Reaction depends on how easily electrons are lost

Answer 5

Be: does not react with water or steam.

Mg: reacts very slowly with water but reacts quickly with steam.

Ca: reacts steadily with cold water.

Sr and Ba: react vigorously with cold water.

Sr(s) + 2H2O(l) Sr(OH)2(aq) + H2(g)
Ba(s) + 2H2O(l) Ba(OH)2(aq) + H2(g)

The hydroxides produced make the water alkaline (if they are soluble in water)

Question 6

Observations

Answer 6

• fizzing, (more vigorous down group)
• the metal dissolving, (faster down group)
• the solution heating up (more down group)
• with calcium a white precipitate appearing (less precipitate forms down group with other metals)

Question 7

Solubility of hydroxides

Answer 7

Mg(OH)2
Sparingly soluble

Ca(OH)2
Slightly soluble

Sr(OH)2
Soluble

Ba(OH)2
Soluble

↓ Solubility increases

All Group 2 hydroxides when not soluble, appear as white precipitates.

  eg Mg2+(aq) + 2OH-(aq)  → Mg(OH)2 (S)

Barium hydroxide would easily dissolve in water.
The hydroxide ions present would make the solution strongly alkaline.

Ba(OH)2(s) → Ba2+(aq) + 2OH-(aq)

Question 8

Solubility of sulfates

Answer 8

MgSO4
Soluble

CaSO4
Slightly soluble

SrSO4
Insoluble

BaSO4
Insoluble

↓ Solubility decreases

eg Ba2+(aq) + SO4 2-(aq) → BaSO4(s)

Test for sulfates:
•Add hydrochloric acid (to remove ions which would interfere with the test)
•Add barium chloride (BaCl2)
•Sulfates give a white precipitate

Question 9

Uses of Group 2 elements and Group 2 compounds

Answer 9

1. Extraction of Titanium
2. Uses of hydroxides
3. Removal of Sulfur dioxide from flue gases
4. Barium meal

Question 10

1. Extraction of Titanium

Answer 10

Titanium very useful metal bc it is abundant, has a low density and is corrosion resistant –used for making strong, light alloys for use in aircraft for example.

Titanium cannot be extracted with carbon because titanium carbide (TiC) it is formed rather than titanium .

Titanium cannot be extracted by electrolysis because it has to be very pure.

Magnesium is used as part of the process of extracting titanium form its ore.

Question 12

Steps in extracting titanium

Answer 12

1. Solid ore converted into chloride (liquid state)

TiO2 (s) + 2Cl2(g) + 2C(s) → 900oC TiCl4(l) + 2CO(g)

2. Chloride is purified by fractional distillation in an argon atmosphere and then reduced by Mg

TiCl4(L) + 2Mg(L) → 500oC Ti(s) + 2MgCl2(l)

Titanium is expensive because:

• expensive cost of Mg and Ar
• batch process
• high temperatures required in both steps

Question 13

2. Uses of hydroxides

Answer 13

Mg(OH)2: in medicine to alleviate constipation also used in indigestion remedies

Ca(OH)2: in agriculture to neutralise acid soil (slaked lime)

test for CO2 (limewater)

Question 14

3. Removal of Sulfur dioxide from flue gases

Answer 14

Coal and crude oil contain sulfur which burns to produce SO2

Dissolves in moisture causing acid rain

Removed from power station chimneys by reacting with calcium oxide (an alkali)

CaO(s) + SO2(g) → CaSO3(s) (calcium sulfite)

Question 15

4. Barium meal

Answer 15

Barium sulfate absorbs X-rays

Barium meals help diagnose problems with the digestive system.

Ba2+ ions are very toxic.
The technique is harmless because BaSO4 is completely insoluble.