3.2.2 Group 2, the alkaline earth metals

Question 1

What is the trend in atomic radius of the elements Mg-Ba?

Answer 1

Atomic radius increases down the group because each element has an extra filled main level of electrons compared with the one above it

Question 2

What is the trend in first ionisation energy of the elements Mg-Ba?

Answer 2

First ionisation energy decreases down the group

because it takes less energy to remove the electrons as they become further and further away from the positive nucleus,

the nucleus is more effectively shielded by more inner shells of electrons

Question 3

What is the trend in melting point of the elements Mg-Ba?

Answer 3

The basic reaction is as follows, where M is any Group 2 metal:
M(s) + 2H2O(l) -> M(OH)2(aq) + H2(g)

The metals get more reactive going down the group and react with water more vigorously.

Magnesium also reacts rapidly with steam to form an alkaline oxide and hydrogen:
Mg(s) + H2O(g) -> MgO(s) + H2(g)

Question 4

Why is magnesium used in the extraction of titanium?

Answer 4

Carbon cannot be used- titanium reacts with carbon to form titanium carbide which makes the metal brittle
TiCl4(l) + 2Mg(s) -> 2MgCl2(s) + Ti(s)

Question 5

What are the solubilities of the hydroxides of the elements Mg-Ba in water?

Answer 5

more soluble going down the group:
Mg(OH)2 is almost insoluble
Ca(OH)2 is sparingly soluble
Sr(OH)2 is soluble
Ba(OH)2 is soluble

Question 6

Give one use of Mg(OH)2 ,Ca(OH)2
,CaO or CaCO3

Answer 6

Medicine - milk of magnesia

• indigestion remedies to neutralise excess stomach acid

-Agriculture - Treating acidic soil
Removing SO2 from flue gases

Question 7

What are the solubilities of the sulfates of the elements Mg-Ba in water?

Answer 7

become less soluble going down the group:
MgSO4 is soluble
CaSO4 is sparingly soluble
SrSO4 is insoluble
BaSO4 is insoluble

Question 8

How to test for sulfate ions?Why is BaCl2 solution used to test for sulfate ions?

Answer 8

Add acidified BaCl2 solution, white precipitate forms
Sulfate ions react with aqueous barium ions in BaCl2 solution to form a precipitate of the insoluble BaSO4

Question 9

Why is the BaCl2 solution acidified?

Answer 9

Dilute hydrochloric acid or nitric acid added to sulfate solution - rid of any soluble carbonate or hydroxide impurities
- interfere with the test by forming insoluble barium carbonate or barium hydroxide.

Question 10

Give one use of BaSO4

Answer 10

Barium meal’ to outline the gut in medical X-rays