Reactions of Period 3 elements with water and oxygenAQA A-Level Chemistry: Subtopic test

1. 1
   A teacher demonstrates the reactions of small pieces of sodium and of magnesium ribbon with cold water, in separate troughs, adding universal indicator to each.

   (a)

   Which equation represents the reaction of sodium with water?

   [1 mark]

   • A2Na + 2H₂O → 2NaOH + H₂
   • BNa + H₂O → NaOH + H₂
   • CNa + 2H₂O → Na(OH)₂ + H₂
   • D2Na + H₂O → Na₂O + H₂

   (b)

   Which observation is made when magnesium reacts with cold water, compared with sodium?

   [1 mark]

   • AMagnesium reacts faster and melts into a ball
   • BMagnesium reacts vigorously and the hydrogen ignites
   • CMagnesium forms a strongly alkaline solution of pH 14
   • DMagnesium reacts very slowly, with few bubbles, forming a weakly alkaline solution

   (c)

   Explain why sodium reacts more vigorously with water than magnesium does.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student heats small samples of magnesium ribbon, aluminium powder, silicon and sulfur in separate combustion spoons in oxygen, in a fume cupboard.

   (a)

   Which description is correct for magnesium burning in oxygen?

   [1 mark]

   • AA yellow flame and a white solid
   • BA bright white flame and a white solid
   • CA blue flame and a colourless, choking gas
   • DA red glow and a brown solid

   (b)

   What is the main product when sulfur burns in oxygen with no catalyst?

   [1 mark]

   • ASO₃
   • BH₂S
   • CSO₂
   • DSO₄²⁻

   (c)

   Write equations for the reactions of aluminium and of silicon with oxygen.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student compares how readily the Period 3 elements react with oxygen. She notes that sodium and magnesium burn vigorously, that phosphorus burns to give white fumes, and that aluminium foil stays unreactive in air at room temperature even though aluminium is a reactive metal.

   (a)

   Write an equation for the burning of phosphorus in excess oxygen, state the oxidation state of phosphorus in the product and state what is seen.

   [3 marks]

   (b)

   Explain why aluminium foil appears unreactive in air at room temperature, and suggest why aluminium powder burns brightly when heated in oxygen.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A chemistry class investigates Period 3 elements. They record that sodium and magnesium both react with water, that sodium burns in oxygen with a yellow flame, that magnesium burns with a bright white flame, and that sulfur burns with a blue flame to give a choking gas.

   (a)

   Compare the reactions of sodium and magnesium with water and with oxygen. Include observations and equations, and explain the difference in reactivity.

   [6 marks]

   (b)

   Write equations for the reactions of sodium, aluminium, phosphorus (P₄) and sulfur with oxygen. Deduce the oxidation state of each element in its product and explain why burning sulfur does not form SO₃.

   [6 marks]

   Total for question 4: 12 marks

End of questions