OxfordAQA International A Level Chemistry
OxfordAQA International A Level Chemistry 3.2.4 Properties of Period 3 Elements and Their Oxides and Chlorides Exam Questions
Free OxfordAQA International A Level Chemistry revision for 3.2.4 Properties of Period 3 Elements and Their Oxides and Chlorides: what you need to know, common mistakes and exam-style questions with answers. Covers reactions of Period 3 elements, structures and melting points of their oxides, and reactions of oxides and chlorides.
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About OxfordAQA International A Level Chemistry 3.2.4 Properties of Period 3 Elements and Their Oxides and Chlorides
This A2 inorganic chemistry topic, examined in Unit 3, extends the periodicity work from Unit 1. You need to describe the reactions of sodium and magnesium with water, and of sodium to sulfur with oxygen and with chlorine. You also need to explain the trend in melting points of the oxides in terms of structure and bonding, describe how the oxides and chlorides react with water and the pH of the resulting solutions, and write equations for the reactions of the oxides with acids and bases. The topic shows the change from ionic, basic oxides to covalent, acidic oxides across the period, with amphoteric aluminium oxide in between.
What you need to know
- Reactions with water Sodium reacts vigorously with cold water: 2Na + 2H2O → 2NaOH + H2. Magnesium reacts very slowly with cold water but burns in steam to give MgO and H2.
- Reactions with oxygen and chlorine The oxides formed are Na2O, MgO, Al2O3, SiO2, P4O10, SO2 and SO3. The chlorides formed are NaCl, MgCl2, Al2Cl6, SiCl4 and PCl5.
- Melting points of oxides Na2O, MgO and Al2O3 have high melting points because they are ionic lattices; MgO is higher than Na2O because of the higher charge on Mg2+. SiO2 is macromolecular with a very high melting point. P4O10 and SO2 are simple molecular with low melting points.
- Oxides with water Na2O gives NaOH (pH about 14) and MgO gives Mg(OH)2 (pH about 9). Al2O3 and SiO2 are insoluble. P4O10 gives H3PO4 and SO2 gives H2SO3 and SO3 gives H2SO4, all acidic (pH 0 to 2).
- Chlorides with water NaCl dissolves to give a neutral solution. MgCl2 gives a slightly acidic solution. Al2Cl6, SiCl4 and PCl5 react (hydrolyse) with water to give strongly acidic solutions containing HCl.
- Acids and bases Basic oxides react with acids, acidic oxides react with bases, and aluminium oxide is amphoteric: it reacts with both acids and bases.
Common mistakes in 3.2.4 Properties of Period 3 Elements and Their Oxides and Chlorides
- Saying SiO2 is acidic because it dissolves in water. It is insoluble but reacts with bases such as NaOH, so it is classed as acidic.
- Explaining the melting point of P4O10 using covalent bonds breaking. Only intermolecular forces are overcome.
- Calling Al2O3 simply basic. It is amphoteric.
- Forgetting that SiCl4 hydrolyses with water, releasing HCl fumes.
Try three 3.2.4 Properties of Period 3 Elements and Their Oxides and Chlorides exam-style questions
1. Write equations for the reactions of Na2O and SO3 with water. (2 marks)
Show the mark scheme answer
Na2O + H2O → 2NaOH; SO3 + H2O → H2SO4.
2. Explain why MgO has a higher melting point than P4O10. (3 marks)
Show the mark scheme answer
MgO is a giant ionic lattice; strong electrostatic attraction between Mg2+ and O2- ions needs a lot of energy to overcome; P4O10 is simple molecular with weak intermolecular forces.
3. 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.
3.2.4 Properties of Period 3 Elements and Their Oxides and Chlorides FAQs
What does OxfordAQA International A Level Chemistry 3.2.4 Properties of Period 3 Elements and Their Oxides and Chlorides cover?
It covers reactions of Period 3 elements, structures and melting points of their oxides, and reactions of oxides and chlorides.
Which unit is 3.2.4 Properties of Period 3 Elements and Their Oxides and Chlorides examined in?
It is examined in Unit 3, an International A2 paper covering inorganic and physical chemistry. The Unit 5 practical and synoptic paper can also assess it.
How do I remember the oxides across Period 3?
Link the bonding to behaviour: ionic oxides of sodium and magnesium are basic, aluminium oxide is ionic with some covalent character and amphoteric, and the covalent oxides of silicon, phosphorus and sulfur are acidic.
