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A-Level Trends in the elements across a period and down a group: worked solution
3 marks. Full working, one step per line.
Question
The oxides across Period 3 show a bonding trend that parallels that of the Period 3 chlorides. For the oxides of sodium, aluminium and phosphorus, describe what happens when each is added to water, provide equations for any reactions taking place, and predict the pH of the solution produced in each case.
Worked answer
Sodium oxide (basic): reacts vigorously with water to give sodium hydroxide, a strong alkali: Na2O + H2O -> 2NaOH; strongly alkaline, pH about 13-14. Aluminium oxide (amphoteric): insoluble and does not react with water, so the mixture stays neutral, pH about 7. Phosphorus(V) oxide (acidic): reacts with water to give phosphoric(V) acid: P4O10 + 6H2O -> 4H3PO4; strongly acidic, pH about 1-2.
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This question is part of A-Level Trends in the elements across a period and down a group, in A-Level H2 Chemistry.
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