2 - Solubility and uses of group 2

Question 1

What is the trend in solubility of the hydroxides down group 2?

Answer 1

Increases down the group

Question 2

Mg(OH)₂ is sparingly soluble. What does this mean?

Answer 2

Its solubility is low

Question 3

What is Mg(OH)₂ used for in medicine?

Answer 3

Used in indigestion tablets to neutralise excess acid in the stomach

Question 4

What is Ca(OH)₂ used for in agriculture?

Answer 4

Used to neutralise acidic soils

Question 5

What is the trend in solubility of the sulfates down group 2?

Answer 5

Decreases down the group

Question 6

What group 2 sulfate is insoluble?

Answer 6

BaSO₄

Question 7

What is BaSO₄ used for in medicine?

Answer 7

• Patients are given a suspension of Barium sulfate
• This coats tissues in the body
• Barium sulfate absorbs X-rays allowing the digestive tract to be seen

Question 8

What is acidified BaCl₂ used for?

Answer 8

To test for sulfate ions

Question 9

How do we know that sulfate ions are present when BaCl₂ is added?

Answer 9

A white precipitate of BaSO₄ will form as the Ba²⁺ ions will react with the SO₄^2- ions
Ba²⁺ _(aq) + SO₄^2- _(aq) → BaSO_4(s)

Question 10

Why does the BaCl₂ need to acidified with HCl first?

Answer 10

To get rid of any sulfites or carbonates that may produce a white precipitate, showing a false positive result

Question 11

How is magnesium used to extract titanium from its ore?

Answer 11

Mg is used as a reducing agent where it will reduce the titanium choride to titanium

Question 12

Give the oxidation of Mg half equation, the reduction of Ti half equation and the overall redox equation showing the extraction of titanium

Answer 12

Oxidation
2Mg → 2Mg²⁺ + 2e^-
Reduction
TiCl₄ + 4e^- → Ti
Overall redox
TiCl₄ + 2Mg → 2MgCl₂ + Ti

Question 13

Why is titanium expensive?

Answer 13

• Mg is expensive
• High temperatures are required as a furnace is required

Question 14

What can CaO or CaCO₃ be used for?

Answer 14

To remove SO₂ from flue gases

Known as ‘flue gas desulfurisation’

Question 15

Give the equation showing the reaction between CaO and SO₂ in flue gas desulfurisation
State an advantage and a disadvantage of this reaction

Answer 15

CaO _(s) + SO_{2 (g)} → CaSO_{3 (s)}
Advantage: Removes SO₂ and prevents acid rain
Disadvantage: CaSO₃ is waste and is put in landfill

Question 16

Give the equation showing the reaction between CaCO₃ and SO₂ in flue gas desulfurisation
State an advantage and 2 disadvantages of this reaction

Answer 16

CaCO_{3 (s)} + SO_{2 (g)} → CaSO_{3 (s)} + CO_{2 (g)}
Advantage: Removes SO₂ and prevents acid rain
Disadvantage: CaSO₃ is waste and is put in landfill
Disadvantage: CO₂ is a greenhouse gas and contributes to global warming