A-LevelChemistryGroup 29701/22 · Feb/Mar 2023 · Q211 Marks

The Group 2 elements Mg to Ba are all silvery-white reactive metals.

(a)(i)Draw a labelled diagram to show the bonding and structure of the Group 2 metals at room temperature.[2]
(a)(ii)Explain why Mg has a higher electrical conductivity than Na.[1]
(b)Write an equation for the reaction of magnesium with cold water.[1]
(c)Identify a single reagent that can be used to distinguish separate samples of dilute Mg(NO3)2(aq) and dilute Ba(NO3)2(aq). Explain your answer. reagent explanation[2]
(d)(i)Describe what is observed when SrI2(aq) reacts with concentrated sulfuric acid.[2]
(d)(ii)Compound X, an anhydrous Group 2 bromide, is dissolved in water and titrated against aqueous silver nitrate. A solution containing 0.250g of X requires 33.65cm³ of 0.0500 moldm-3 AgNO3(aq) for complete reaction. Identify X. Show your working. X =[3]

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2023). The mark or mark type is shown in brackets.

[1] 2(a)(i) M1 diagram showing minimum of 4 particles (in total in 2 rows) labelled 'ion' or '+'
[1] 2(a)(i) M2 delocalised electrons shown as e⁻/– OR little circles labelled electrons AND labelled 'delocalised electrons'
[1] 2(a)(ii) Mg has more delocalised e⁻ (than Na)
[1] 2(b) Mg + 2H2O → Mg(OH)2 + H2
[1] 2(c) reagent = any named/formula of soluble sulfate OR H2SO4 OR any named/formula of soluble hydroxide
[1] 2(c) BaSO4 insoluble (& MgSO4 soluble) OR (Ba(OH)2 soluble &) Mg(OH)2 insoluble
[2] 2(d)(i) white precipitate / yellow solid / effervescence / misty fumes / (dark) grey solid / purple gas / rotten egg smell (any two distinct observations)
[1] 2(d)(ii) moles of AgNO3 = 33.65/1000 × 0.0500 (= 1.68(25) × 10⁻³)
[1] 2(d)(ii) moles of X = ½ x moles of AgNO3 = 0.250 ÷ Mr(X) :: Mr(X) = 297.2
[1] 2(d)(ii) Ar of Group 2 element is 297.2 – 2(79.9) = 137.4 AND X is BaBr2

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