A-LevelChemistryChemical periodicity9701/22 · Oct/Nov 2017 · Q315 Marks

The elements in Group 2 show trends in their properties that are typical of metals. The elements in Group 17 show trends in their properties that are typical of non-metals. Some reactions based on the Group 2 metal barium, Ba, are shown. [Figure showing reaction scheme: Ba(NO3)2(aq) + H2(g) (reaction 1) → Ba(s) (reaction 2) → Ba(OH)2(aq) + H2(g); also Ba(s) (heat in air) → X(s)]

(a)State and explain the trend in ionisation energy down Group 2.[2]
(b)(i)State and explain the trend in melting point down Group 17.[2]
(b)(ii)The melting point decreases down Group 2. Explain this trend.[2]
(c)(i)State the reagent needed for each of reactions 1 and 2. reaction 1 reaction 2[2]
(c)(ii)Name X and write an equation for its formation. name equation[2]
(c)(iii)The Ba(NO3)2(aq), produced by reaction 1, is heated to dryness. The anhydrous solid is then heated strongly and decomposes. Barium oxide is produced, together with two other products. Identify the two other products of this decomposition reaction and state what would be observed.[2]
(c)(iv)State what would be observed when excess MgSO4(aq) is added to the Ba(OH)2(aq) produced in reaction 2. Explain your answer.[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.

[1] (IE) decreases / lower because increasing distance of outer electron(s) from nucleus OR increasing distance of outer / valence shell from nucleus OR increased shielding / screening (from inner shells)
[1] reduces nuclear attraction (for electrons)
[1] (Melting point) increases / higher because (molecules have an) increasing (number of) electrons
[1] increasing strength / number / amount of IMFs / Van der Waals' / id-id / London / dispersion (forces)
[1] increased metallic / (cat)ionic radius / size OR decreasing (cat)ion charge-density
[1] decreased attraction (of ions) for delocalised / outer electrons
[1] reaction 1: HNO3 or nitric((V)) acid
[1] reaction 2: water / H2O
[1] barium oxide
[1] 2Ba + O2 → 2BaO
[1] NO2 / nitrogen dioxide / nitrogen(IV) oxide AND O2 / oxygen
[1] (red / yellow-)brown gas OR gas given off that relights glowing splint
[1] white ppt / solid / suspension
[1] of BaSO4 / barium sulfate OR Mg(OH)2 / magnesium hydroxide
[1] BaSO4 is insoluble OR Mg(OH)2 is insoluble / partially / slightly / sparingly soluble

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