AQA A Level Chemistry
AQA A Level Chemistry 3.2.4 Properties of Period 3 Elements and Their Oxides Exam Questions
Free AQA A Level Chemistry exam questions for 3.2.4 Properties of Period 3 Elements and Their Oxides, with a mark scheme for every pack. Covers Period 3 elements with water and oxygen, oxide structures and melting points, and acid-base reactions of oxides.
3.2.4 Properties of Period 3 Elements and Their Oxides exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA A Level Chemistry 3.2.4 Properties of Period 3 Elements and Their Oxides
This A Level inorganic topic on the AQA course builds on 3.2.1 Periodicity. You need the reactions of sodium and magnesium with water, the reactions of Period 3 elements with oxygen, and the formulae, structures and melting points of the oxides from Na2O to SO3. You then link structure and bonding to the behaviour of the oxides in water, the pH of the solutions formed, and their reactions with acids and bases, including the amphoteric nature of aluminium oxide. Examiners ask for balanced equations, approximate pH values, explanations of melting point in terms of structure, and equations showing acidic, basic and amphoteric behaviour.
What you need to know
- Reactions with water Sodium reacts vigorously with cold water: 2Na + 2H2O → 2NaOH + H2, giving a pH of about 13 to 14. Magnesium reacts very slowly with cold water to form Mg(OH)2, which is only slightly soluble, giving a pH of about 9 to 10.
- Reactions with oxygen Sodium burns with a yellow flame to form Na2O, magnesium with a white flame to form MgO, phosphorus forms P4O10 and sulfur burns with a blue flame to form SO2. Aluminium forms Al2O3 and silicon forms SiO2.
- Structure and melting points Na2O, MgO and Al2O3 are ionic with high melting points (MgO highest because Mg2+ is small with a 2+ charge). SiO2 is macromolecular with a high melting point. P4O10 and SO2 are simple molecular with low melting points.
- Oxides with water Na2O + H2O → 2NaOH and MgO + H2O → Mg(OH)2 are basic. P4O10 + 6H2O → 4H3PO4 and SO2 + H2O → H2SO3, SO3 + H2O → H2SO4 are acidic, with pH about 0 to 3. Al2O3 and SiO2 are insoluble.
- Acid-base behaviour Basic oxides react with acids, e.g. MgO + 2HCl → MgCl2 + H2O. SiO2 is acidic and reacts with hot concentrated NaOH: SiO2 + 2NaOH → Na2SiO3 + H2O. Al2O3 is amphoteric, reacting with acids and with bases: Al2O3 + 2NaOH + 3H2O → 2NaAl(OH)4.
Common mistakes in 3.2.4 Properties of Period 3 Elements and Their Oxides
- Saying silicon dioxide dissolves in water to form an acid. SiO2 is insoluble; it is classed as acidic because it reacts with bases.
- Writing the oxide of phosphorus as P2O5 in equations when P4O10 is expected. Use P4O10 and form H3PO4 with water.
- Stating that SO2 forms sulfuric acid with water. SO2 forms sulfurous acid, H2SO3; SO3 forms H2SO4.
- Explaining the high melting point of MgO in terms of covalent bonds. It is ionic with strong electrostatic attractions between Mg2+ and O2- ions.
- Forgetting that aluminium oxide is amphoteric and only showing its reaction with acid.
Try three 3.2.4 Properties of Period 3 Elements and Their Oxides exam-style questions
1. Write an equation for the reaction of phosphorus(V) oxide with water and give the approximate pH of the solution formed. (2 marks)
Show the mark scheme answer
P4O10 + 6H2O → 4H3PO4; pH about 0 to 1.
2. Write equations to show that aluminium oxide is amphoteric. (2 marks)
Show the mark scheme answer
Al2O3 + 6HCl → 2AlCl3 + 3H2O; Al2O3 + 2NaOH + 3H2O → 2NaAl(OH)4.
3. Explain why magnesium oxide has a much higher melting point than phosphorus(V) oxide. (3 marks)
Show the mark scheme answer
MgO is ionic with a giant lattice of Mg2+ and O2- ions held by strong electrostatic attractions; P4O10 is simple molecular; only weak intermolecular forces (van der Waals and dipole-dipole) need to be overcome to melt P4O10, which needs much less energy.
3.2.4 Properties of Period 3 Elements and Their Oxides FAQs
What does AQA A Level Chemistry 3.2.4 Period 3 Elements and Oxides cover?
It covers reactions of Period 3 elements with water and oxygen, the structure and melting points of their oxides, the pH of solutions formed with water, and the acid-base reactions of the oxides.
Which paper is 3.2.4 Period 3 Elements and Oxides examined in?
It is examined in Paper 1, and Paper 3 can also include it.
How do I learn the oxide equations efficiently?
Make a table with each oxide, its structure, its reaction with water and the pH, and its reaction with acid or base. Link the change from basic to acidic across the period to the change from ionic to covalent bonding.
