9.1 - Trends and Uses of group 2 elements

Question 1

Uses of calcium in agriculture

Answer 1

• limestone (impure CaCO3)
• quick lime (CaO - thermal decomposition of CaCO3)
• slaked lime - Ca(OH)2 formed when water added to quicklime

all three are used to raise the pH of the soil - becomes more acidic overtime

Question 2

Uses of barium in screening

Answer 2

• used in medicine in the form of BaSO4 - swallowed and is given to a patient which requires an X-ray and their intestines are imaged
• toxic however so it’s insoluble so it’s not absorbed into the blood and a small sample is given
• can also be used for test of sulphate ions

Question 3

Uses of magnesium in the human body

Answer 3

• partially soluble in water and can be used in milk of magnesia to neutralise excess stomach acid and treat constipation

Mg(OH)2(s) + 2HCl (aq) → MgCl2(aq) + 2H2O (l)

• only partially soluble making the solutions slightly alkaline due to the low OH- conc. so Mg(OH)2 is safe to use

Question 4

Uses of magnesium in extraction

Answer 4

also used in extraction of titanium from its ore
* heated in a stream of chlorine in the presence of coke to produce TiCl4
* TiO2(s) + 2C (s) + 2Cl2(g) → TiCl4(g) + 2CO (g)
* it is then reduced using magnesium to form titanium

TiCl4(g) + 2Mg (l) → Ti (s) + 2MgCl2(l)

Question 5

Uses of calcium in removal of gases

Answer 5

also used for removing SO2 from flue gases (scrubbing)

Question 6

what do all group 2 elements have?

Answer 6

has two electrons within its outer shell

Question 7

What can all group 2 elements form?

Answer 7

ionic compounds
* donate two electrons to the other element from its outermost shell to become a 2+ charged ion

Question 8

What can group 2 metals be within reactions?

Answer 8

reducing agents

Question 9

what happens going down group 2?

Answer 9

become more reactive

Question 10

Ionisation energy trends in group 2

Answer 10

going down the group the ionisation energy decreases (increased shielding effect and larger distance between outer electrons) - nucleus outweighs the attraction of the higher nuclear charge

Question 11

Radius of group 2 elements going down the group and what happens as a result

Answer 11

• increases as the outermost electron gets further away
• melting point as a result decreases as the attraction between the nucleus and the bonding electrons decreases

Question 12

What happens to the density of the alkali earth metals

Answer 12

decreases and then increases

Question 13

Group 2 hydroxide solubility

Answer 13

group 2 oxides with water become more alkaline

O2-(aq) + H2O (l) → 2OH-(aq)

the higher the concentration of hydroxide ions - the more alkaline and the solubility increases

Question 14

Group 2 sulphates solubility

Answer 14

decreases going down the group