Oxygen is the most abundant element in the Earth's crust. It reacts with other elements to form stable compounds, ions and molecules.

1. (a)Complete the table to give the formulae and acid/base behaviour of some of the oxides of the Period 3 elements. | element | sodium | aluminium | silicon | phosphorus | sulfur | |---|---|---|---|---|---| | formula of oxide | Na2O | | | | SO3 | | acid/base behaviour | | amphoteric | | | |[2]
2. (b)(i)Group 2 elements form stable hydroxides, with general formula M(OH)2, where M is the Group 2 element. Beryllium hydroxide, Be(OH)2, is an amphoteric compound that shows similar chemical reactions to aluminium oxide. State the meaning of the term amphoteric.[1]
3. (b)(ii)Write an ionic equation for the reaction of magnesium hydroxide, Mg(OH)2, with hydrochloric acid.[1]
4. (b)(iii)Two methods of preparing strontium hydroxide are shown. strontium ---H₂O reaction 1---> strontium hydroxide strontium oxide ---H₂O reaction 2---> strontium hydroxide State one difference between the observations you would make for reaction 1 and reaction 2.[1]
5. (b)(iv)State how the solubility of the Group 2 hydroxides changes down the group.[1]
6. (c)(i)Sodium peroxide, Na2O2, reacts with CO2. Na2O2(s) + CO2(g) → Na2CO3(s) + ½O2(g) The partial pressure of CO2(g) in a 0.500 dm³ sample of air is 5.37 kPa at 20°C. Calculate the amount, in moles, of CO2(g) present in the sample of air at 20°C.[2]
7. (c)(ii)Calculate the mass of Na2O2(s) that would react fully with the amount of CO2(g) calculated in (i).[1]
8. (c)(iii)The peroxide ion, O22-, has a single covalent bond between the two oxygen atoms. Each oxygen atom carries a negative charge. Draw a 'dot-and-cross' diagram for the peroxide ion. Show outer electrons only.[2]

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