Inorganic Chemistry
7 marks · EasyThis question requires you to use knowledge of oxides formed by combustion and oxidation/reduction principles.
State whether the oxide formed when sulfur burns in oxygen is acidic or basic, and give a reason.
When magnesium burns in oxygen, what type of oxide is formed? How does it behave in water?
For the reaction: Zn(s) + CuO(s) → ZnO(s) + Cu(s) Explain in terms of oxygen transfer which substance is oxidised and which is reduced.
Give the definition of oxidation in terms of electron transfer, and state which substance is oxidised in the reaction in (c).
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(a) Acidic; because sulfur is a non-metal and its oxide, sulfur dioxide, forms acidic solution.
(b) A basic oxide (magnesium oxide) is formed; it is slightly soluble and forms an alkaline solution in water.
(c) Zinc is oxidised because it gains oxygen to form zinc oxide. Copper(II) oxide is reduced because it loses oxygen to form copper metal.
(d) Oxidation is the loss of electrons; zinc is oxidised because it loses electrons.
Common mistakes: Incorrectly identifying type of oxide; Omitting explanation of oxygen transfer; Not linking oxidation to electron loss
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Marking points
A1 (a) · 1 mark · Identifies sulfur oxide as acidic
A2 (a) · 1 mark · Gives correct reason (non-metal oxide forms acid in water)
B1 (b) · 1 mark · States MgO is basic
B2 (b) · 1 mark · States its behaviour: forms (slightly soluble) alkaline solution in water
C1 (c) · 1 mark · Explains zinc is oxidised by gaining oxygen
C2 (c) · 1 mark · Explains copper(II) oxide is reduced by losing oxygen
D1 (d) · 1 mark · States oxidation is loss of electrons; identifies zinc
Worked solution
a) The oxide of sulfur (sulfur dioxide) is acidic because it is a non-metal oxide and forms acidic solutions.
b) Magnesium forms a basic oxide (MgO) which dissolves just a little in water to give an alkaline solution.
c) In the reaction, zinc is oxidised because it gains oxygen and is converted into zinc oxide. Copper(II) oxide is reduced because it loses oxygen and forms copper metal.
d) Oxidation is defined as loss of electrons. In this reaction, zinc is oxidised as it loses electrons.