3.1.2 Group 2

Question 1

How are group 2 ions formed?

Answer 1

• electron lost from s orbital to form 2+ ion ‘s’ block
• lost in redox reactions

Question 2

What are properties of group 2 reactions?

Answer 2

• high mpt and bpt
• colourless compound
• low density

Question 3

What are the ionisation energies of group 2 elements?

Answer 3

IE for 1st and 2nd ionisation decrease down the group from Mg to Ba
- shielding increases
- e- in higher energy level
- larger atomic radius
M(g) -> M+(g) + e-
M+(g) -> M2+(g) + e-
Reactivity increases as ionisation energy decreases

Question 4

Redox reaction with oxygen

Answer 4

2Mg(s) + O2(g) -> 2MgO(s)
Burns in air with white light to give a white powder

Question 5

Redox reaction with water

Answer 5

Ca(s) + 2H2O(l) -> Ca(OH)2(aq) + H2(g)
Be doesn’t react with water, Mg reacts with steam, metals react with increased vigour down the group
Same applies to dilute acids

Question 6

Redox reaction with acids

Answer 6

Ba(s) + 2HCl(aq) -> BaCl2(aq) - H2(g)

Question 7

Reaction of water with group 2 oxides

Answer 7

MO(s) + H2O(l) -> M(OH)2(g)
pH =10-12
Low solubility and alkalinity (conc of OH- ions)
Mg(OH)2 (slightly soluble and very low OH-)
I
Ba(OH)2 (more soluble and higher OH-)

BeO doesn’t react with H2O

Question 8

Uses of group 2 compounds

Answer 8

Ca(OH)2 in agriculture to neutralise acid soils
Mg(OH)2 and CaCO3 to treat indigestion by neutralising stomach acid
CaCO3(s) + 2H+(aq) -> Ca2+(aq) + CO2(g) + H2O(l)
CaCO3 also used in the building industry (limestone/marble but can be destroyed by rain)
CaCO3 is also used in the manufacture of steel and glass