Group 2 (Alkaline Earth Metals)

Question 1

State and explain the trend in atomic radius down group 2

Answer 1

• increases
• number of filled electron shells increases down the group

Question 2

State and explain the trend in 1 st ionisation energy down group 2

Answer 2

• decreases down the group
• Electron shielding and radius increases
• Electrostatic attraction between nucleus and outer electron is weaker
• easier/less energy to remove the outer electron

Question 3

State and explain the trend in melting point down group 2

Answer 3

• Melting point decreases down the group (with exception of Mg which is lower than expected).
• Size of ion increases the distance between nucleus and delocalised electron field
• Weaker electrostatic attraction requiring less energy to overcome

Question 4

Write a general equation for the reaction of Ca, Sr or Ba with water

Answer 4

M(s) + 2H2O(l) –> M(OH)2 (s) + H2 (g)

Question 5

How is the reaction of Mg with water different than that of Ca, Sr or Ba with water?

Answer 5

Mg will only react with steam not liquid water

Question 6

Describe the reaction of Mg with steam and write an equation

Answer 6

A bright white flame is observed, producing a white solid MgO
Mg(s) + H2O(g) –> MgO(s) + H2 (g)

Question 7

Explain why very clean Mg will have a slow reaction with water

Answer 7

Mg contains an oxide layer that prevents it reacting with water
Cleaning the Mg removes the oxide layer

Question 8

Explain how Mg is used to extract titanium from its ore

Answer 8

TiO2 + 2Cl2 + 2C –> TiCl4 + 2CO
TiCl4 + 2Mg –> Ti + 2MgCl2
Mg is used as the reducing agent rather than C, because carbon reduction also produces titanium carbide (TiC) which is brittle

Question 9

Write a general simplest ionic equation for the reaction of aqueous group 2 ions with sodium hydroxide solution

Answer 9

M2+ (aq) + 2OH - (aq) –> M(OH)2 state of product depends on solubility of hydroxide

Question 10

State the trend in solubility of hydroxides of group 2

Answer 10

Increases down the group Mg(OH) 2 is insoluble (s), Ba(OH) 2 is soluble (aq)

Question 11

Give a use of Mg(OH) 2 in medicine

Answer 11

Milk of magnesia, neutralises excess stomach acid (antacid tablets)

Question 12

Give a use of Ca(OH) 2 in agriculture

Answer 12

Used to neutralise acidic soils for growing crops

Question 13

How are CaO and CaCO3 used to remove acidic flue gases (SO2) from coal burning emissions?

Answer 13

Flue gases bubbled through a slurry of CaO or CaCO 3 . Produces a precipitate
CaO + SO 2 –> CaSO3
CaCO3 + SO2 –> CaSO3 + CO2

Question 14

Write the simplest ionic equation for the reaction of acidified barium chloride with sulfate ions or sulfuric acid and give an observation

Answer 14

Ba2+ (aq) + SO4 2- (aq) –> BaSO 4 (s)
White precipitate formed

Question 15

State the trend in solubility of the group 2 sulfates

Answer 15

Decrease in solubility down the group

Question 16

Explain why barium chloride solution used to test for sulfate ions must be acidified

Answer 16

Prevents the formation of a white ppt of BaCO3
This is formed when atmospheric CO 2 dissolves in the solution

Question 17

Give a use for barium sulfate in medicine and explain why it is suitable for this purpose

Answer 17

Barium meal. It is dense and absorbs X-rays
Insoluble and therefore non-toxic

Question 18

Why is the 2nd ionisation energy for magnesium is more endothermic than the 1st?

Answer 18

• removal of an electron from a Mg+ ion rather than a Mg atom
• stronger electrostatic attraction due to greater effective nuclear charge