A student set up a tube as shown in the diagram. [Figure A5.1: Diagram showing a long horizontal tube with cotton wool soaked in hydrobromic acid at the left end, and cotton wool soaked in aqueous ammonia at the right end. A point X is marked closer to the hydrobromic acid end.] Concentrated hydrobromic acid produces fumes of hydrogen bromide. Concentrated aqueous ammonia produces fumes of ammonia.

1. (a)After some time, solid ammonium bromide appeared on the walls of the tube at point X. Use the kinetic particle theory to explain this result.[4]
2. (b)A gas syringe is filled with 70cm³ of ammonia gas. The pressure on the plunger is increased. The temperature does not change but the volume in the syringe decreases to 60 cm³. [Figure A5.2: Diagram of a gas syringe. Initial volume 70 cm³ with plunger up, final volume 60 cm³ with plunger pushed down. Ammonia gas is inside.] Use the kinetic particle theory to explain why the volume decreases.[1]

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