1.3.2 - Group 2

Question 1

1. Describe the rection between Ca and O₂.
2. Write a balanced equation for this reaction.
3. State what type a reaction this is and explain your answer.

Answer 1

1. Group 2 elements react vigorously with oxygen and Ca is a group 2 element.
2. 2Ca (s) + O₂ (g) → 2CaO (s)
3. This is a redox reaction. This is because the Ca loses two electrons each, meaning it is being oxidised. The O₂ gains two electrons each, meaning it is being reduced.

Question 2

1. Describe an observation you will see when Ca reacts with H₂O.
2. Write a balanced equation between Ca and H₂O.
3. Use oxidation numbers to identify which is the reducing agent. Explain your answer.

Answer 2

1. When group 2 elements react with water, a gas (hydrogen) will form, causing ‘fizzing’ or bubbles.
2. 2Ca (s) + 2H₂O(l) → Ca(OH) (aq) + H₂ (g)
3. One H atom from the H2O gains one electron, meaning it is reduced. The Ca gives the H this electron, meaning it is the reducing agent.

Question 3

Describe and explain the trend in reactivity down the Group 2 elements in terms of ionisation energies only.

Answer 3

• Describe - As you go down the Group 2 elements, the reactivity increases.
• Explain - This is mainly because the ionisation energies decrease as you go down the group (excluding radium), which means that the 2 outer shell electrons become easier to remove for a reaction.

Question 4

Describe the effect water has on Group 2 oxides:

• Name what they form.
• State the pH of their product.

Answer 4

• Group 2 oxides and water form a metal hydroxide solution.
• It usually has a pH of 10-12.
• (Group 2 oxides and hydroxides are bases.)

Question 5

1. Magnesium carbonate is decomposed by heat. Write an equation to show this.
2. What is this reaction called?

Answer 5

1. MgCO₃ (s) → MgO (s) + CO₂ (g)
2. This reaction is called thermal decomposition.

Question 6

Describe the trend of the diffculty in decomposing group 2 carbonates with heat as you go down the group.

Answer 6

The carbonates become harder to decompose with heat as you go down the group.

Question 7

Group 2 hydroxides dissolve in water to form alkaline solutions. Describe the solubility of the hydroxides in water as you do down the group and level of alkalinity.

Answer 7

• The solubility of Group 2 hydroxides in water increases as you go down the group.
• The level of alkalinity also increases.

Question 8

Explain the use of Ca(OH)₂ and Mg(OH)₂.

Answer 8

• Ca(OH)2 is used by farmer to neutralise acid soils.
• Mg(OH)2 is used in ‘milk of magnesia’ to relieve indigestion by neutralising the excess acid in the stomach.