Module 5 · Answers
Answers & explanations
Section A — Easy
01
metal + acid → salt + hydrogen
02
Hold a lit splint at the mouth of the test tube — a "squeaky pop" indicates hydrogen.
03
Zinc sulfate.
04
e.g. potassium, sodium, magnesium, iron, copper (any five in correct order).
05
Ceramic — brittle. Polymer — flexible. Composite — two materials combined.
Section B — Medium
06
The blue colour fades and a brown coating of copper appears on the magnesium.
magnesium + copper sulfate → magnesium sulfate + copper
magnesium + copper sulfate → magnesium sulfate + copper
07
(a) No reaction — iron is less reactive than magnesium.
(b) Reaction occurs — zinc is more reactive than copper, so it displaces copper.
(c) No reaction — silver is less reactive than iron.
(b) Reaction occurs — zinc is more reactive than copper, so it displaces copper.
(c) No reaction — silver is less reactive than iron.
08
Gold is very unreactive, so it doesn't combine with oxygen or other elements — it stays as the metal. Iron is reactive, so it always reacts with oxygen in the air or compounds in the rock.
09
Iron is less reactive than carbon, so carbon can take the oxygen from iron oxide. Aluminium is more reactive than carbon, so carbon won't pull the oxygen off — electrolysis is needed instead.
10
(a) Polymer / wood — heat insulator and won't burn easily.
(b) Composite (carbon-fibre) or aluminium alloy — light and strong.
(c) Polymer (e.g. PET) — light, flexible, doesn't break, cheap.
(b) Composite (carbon-fibre) or aluminium alloy — light and strong.
(c) Polymer (e.g. PET) — light, flexible, doesn't break, cheap.
Section C — Hard
11
Order of reactivity (most to least): X > Y > Z. The faster the reaction with acid, the more reactive the metal. Z gives no reaction so it is below hydrogen in the reactivity series.
12
copper oxide + carbon → copper + carbon dioxide. Copper oxide has been reduced (oxygen removed).
13
The aggregate (sand and gravel) reinforces the brittle cement, so concrete is much stronger than cement alone. It's also cheap, can be moulded into shape, and is durable.
14
Saves a lot of energy compared with extracting from ore (less electricity needed). Conserves limited bauxite reserves. Reduces waste sent to landfill.