3.2.2 Group 2 PPQs

Question 1

Why does the gas turn damp litmus paper blue when NH4+ is heated with NaOH?

Answer 1

Formation of NH3, Ammonia gas

Question 2

Describe the bonding in magnesium.

Answer 2

Attraction between lattice of Mg2+ ions and delocalised

Question 3

State what is observed when dilute aqueous sodium hydroxide is added to separate solutions of magnesium chloride and barium chloride.

Answer 3

Observation with MgCl2: white ppt
Observation with BaCl2: no visible change

Question 4

Describe how a student could distinguish between aqueous solutions of magnesium chloride, MgCl2, and aluminium chloride, AlCl3, using one simple test-tube reaction.

Answer 4

NaOH
white precipitate / white solid with MgCl2
(white) ppt which dissolves in excess (NaOH) with AlCl3

Question 5

Similar-sized pieces of barium and magnesium are added to separate samples of sulfuric acid. The barium reacts quickly at first but stops after a few minutes, even though there is still some unreacted barium in the flask. The magnesium reacts more slowly than the barium, but the reaction continues until all the magnesium has reacted. Explain why the barium initially reacts more quickly and why it stops reacting.

Answer 5

• Barium is more reactive because valence electrons are further from the nucleus so are lost more easily
• insoluble barium sulfate is formed and coats the barium, preventing further reaction