O-LevelChemistryMetals & Reactivity5070/21 · May/June 2019 · Q212 Marks

The table shows some of the properties of the elements in Group II of the Periodic Table. | element | proton (atomic) number | atomic radius /nm | melting point /°C | |:--------|:-----------------------|:------------------|:------------------| | Be | 4 | 0.089 | 1280 | | Mg | 12 | 0.136 | 650 | | Ca | 20 | 0.174 | 850 | | Sr | 38 | 0.191 | 768 | | Ba | 56 | 0.198 | 714 | | Ra | 88 | | |

(a)Explain why the elements in Group II have similar chemical properties.[1]
(b)Explain why it is easier to predict the atomic radius of radium, Ra, than the melting point of radium.[1]
(c)(i)Magnesium chloride contains Mg²⁺ and Cl⁻ ions. Write the electronic configuration for a magnesium ion.[1]
(c)(ii)Magnesium is produced by the electrolysis of molten magnesium chloride. Construct equations for the reactions taking place at the: negative electrode positive electrode.[2]
(d)Magnesium reacts with aqueous copper(II) sulfate in a redox reaction. Mg(s) + Cu²⁺(aq) → Mg²⁺(aq) + Cu(s) Which particle is reduced? Explain your answer.[1]
(e)Magnesium reacts with steam. Name the products of this reaction.[1]
(f)Calcium reacts with cold water. Write the equation for this reaction.[1]
(g)Magnesium chloride is a soluble salt. Describe how a pure sample of magnesium chloride crystals can be made from magnesium.[4]

Mark scheme

Marking points from the official mark scheme (May/June 2019). The mark or mark type is shown in brackets.

[1] all have 2 electrons in their outer shell (1)
[1] atomic radius is always increasing / the melting point goes up and down (1)
[1] 2.8 (1)
[2] negative electrode: Mg²⁺ + 2e⁻ → Mg (1)
[2] positive electrode: 2Cl⁻ → Cl₂ + 2e⁻ (1)
[1] Cu²⁺
[1] because it gains electrons (1)
[1] magnesium oxide and hydrogen (1)
[1] Ca + 2H₂O → Ca(OH)₂ + H₂ (1)
[4] use hydrochloric acid (1)
[4] use excess magnesium (1)
[4] filter (off magnesium) (1)
[4] leave filtrate in warm place / evaporate solution to point of crystallisation then leave (1)

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