Group 2 chemistry

Question 1

How does 1st ionisation energy change down group 2?

Answer 1

It decreases.
-Electron shielding increases
-Outer electron feels weaker attraction from nucleus
-Outer electron requires less energy to remove

Question 2

How does melting point change down group 2?

Answer 2

It decreases (except for Mg’s which is lower than expected)
-Radius increases
-Distance between nucleus and sea of delocalised electrons increases
-Weaker attraction keeping ions in the lattice which requires less energy to break

Question 3

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

Answer 3

M(s) + 2H₂O(l) → M(OH)₂(s) + H₂(g)

Question 4

What is unique about Mg’s reaction with H₂O?

Answer 4

It can only react with steam

Question 5

Which element in group 2 will only react with steam?

Answer 5

Mg

Question 6

Write an equation for the reaction of Mg with H₂O

Answer 6

Mg(s) + H₂O(g) → MgO(s) + H₂(g)
(Mg only reacts with steam)

Question 7

Give observations for the reaction of Mg with H₂O

Answer 7

Bright white flame producing a white solid (MgO)

Question 8

Explain why a clean strip of Mg will react slowly with liquid water.

Answer 8

Unclean Mg has a layer of MgO surrounding it which does not react with water
Cleaning it with sandpaper exposes the pure Mg

Question 9

How is Mg used to extract titanium from rutile?

Answer 9

TiO₂ + 2Cl₂ + 2C → TiCl₄ + 2CO
TiCl₄ + 2Mg → Ti + 2MgCl₂
MG is used as a reducing agent as using C would produce brittle TiC.

Question 10

How does the solubility of hydroxides change down group 2?

Answer 10

It increases
Mg(OH)₂ is insoluble
Ba(OH)₂ is soluble

Question 11

Give a use of Mg(OH)₂in medicine

Answer 11

Milk of magnesia, neutralises excess stomach acid

Question 12

What compound is used to neutralise excess stomach acid?

Answer 12

Mg(OH)₂
(Milk of magnesia)

Question 13

Give a use of Ca(OH)₂ in agriculture

Answer 13

Used to neutralise acidic soils

Question 14

What compound is used to neutralise acidic soils in agriculture?

Answer 14

Ca(OH)₂

Question 15

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

Answer 15

CaO + SO₂ → CaSO₃
CaCO₃ + SO₂ → CaSO₃ + CO₂

Question 16

Write the simplest ionic equation for the reaction of acidified BaCl₂ and H₂SO₄ and give an observation

Answer 16

Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
White precipitate formed (BaSO₄)

Question 17

State the trend in solubility of the group 2 sulfates

Answer 17

Decreases down the group
MgSO₄ is soluble
BaSO₄ is insoluble

Question 18

Explain why BaCl₂ is acidified when testing for sulfates

Answer 18

To prevent the formation of BaCO₃ which is a white precipitate
Formed when CO₂ from the atmosphere is dissolved

Question 19

Give a use of BaSO₄ in medicine and explain why it is suitable

Answer 19

Barium meal used in digestive tract imaging.
It is dense and absorbs X-rays
It is insoluble and therefore non-toxic

Question 20

What compound is used in digestive tract imaging and why?

Answer 20

BaSO₄
It is dense and absorbs X-rays
It is insoluble and therefore non-toxic