I- Group 2 =)

Question 1

Calcium carbonate is an insoluble solid that can be used in a reaction to lower the acidity of the water in a lake.
Explain why the rate of this reaction decreases when the temperature of the water in the lake falls. (3)

Answer 1

• ions ↓ ke
• ↓ ions w/ energy ≥ activation energy
• ↓ successful collisions

Question 2

Explain why strontium has a higher melting point than barium. (2)

Answer 2

• delocalised e- closer to nucleus
• ↑ attraction between +ve ions & delocalised e- –> stronger metallic bonds

Question 3

The excess of magnesium used in Titanium extraction can be removed by reacting it with dilute sulfuric acid to form magnesium sulfate.
Use your knowledge of group 2 sulfates to explain why the magnesium sulfate formed is easy to separate from the titanium. (1)

Answer 3

Soluble –> washed away

Question 3

State how barium sulfate is used in medicine.
Explain why this use is possible, given that solutions containing barium ions are poisonous. (2)

Answer 3

• Barium meal in X-rays
• BaSO4 is insoluble- x toxic

Question 4

State one observation when magnesium reacts with steam. (1)

Answer 4

• bright white light
• (white powder)

Question 5

Give an equation to show how magnesium is used as the reducing agent in the extraction of titanium.
Explain, in terms of oxidation states, why magnesium is the reducing
agent. (2)

Answer 5

• 2Mg + TiCl4 → 2MgCl2 + Ti
• Mg oxidation state: 0 –> +2 so e- lost /
• Ti oxidation state: +4 –> 0 so gains e-

Question 6

Explain why calcium has a higher melting point than strontium. (2)

Answer 6

• smaller ions
• delocalised e- closer to +ve ions
• stronger attraction between them

Question 7

Solutions of barium hydroxide are used in the titration of weak acids.
State why magnesium hydroxide solution could not be used for this purpose. (1)

Answer 7

insoluble

Question 8

Magnesium burns with a bright white light and is used in flares and fireworks.
Use your knowledge of the reactions of group 2 metals with water to explain why water should not be used to put out a fire in which magnesium metal is burning. (2)

Answer 8

• produces H2
• explosion/ v. flammable

Question 9

State and explain the trend in melting points of the Group 2 elements Ca-Ba. (3)

Answer 9

• ↓ down the group
• larger atoms
• ↓ attraction for decolised e- –> weaker metallic bonding

Question 10

Extraction of Strontium:
3SrO(s) + 2Al(s) –> 3Sr(s) + Al2O3(s)
Suggest one major reason why this method of extracting strontium is expensive. (1)

Answer 10

1. Al extracted by electrolysis- requires ↑ electricity
2. reaction requires heat- endothermic

Question 11

Other than cost, explain one advantage of using magnesium hydroxide rather than magnesium carbonate to reduce acidity in the stomach. (1)

Answer 11

• x produce CO2 (wind)

Question 12

What is the correct observation when barium metal is added to an excess of water? [1 mark]
A Forms a colourless solution only
B Forms a colourless solution and effervesces
C Forms a white precipitate only
D Forms a white precipitate and effervesces

Answer 12

B

Ba(OH)2 + H2O –> Ba2+ +2OH-