O-LevelChemistryMetals & Reactivity5070/21 · Oct/Nov 2021 · Q710 Marks

This question is about metals and metal compounds.

(a)Silver is a transition element. Potassium is a metal in Group I of the Periodic Table. State two differences in the physical properties of silver and potassium.[2]
(b)An ion of silver has the symbol ¹⁰⁹₄₇Ag⁺ Deduce the number of protons, neutrons and electrons in this ion.[3]
(c)Potassium reacts with water to form a gas which 'pops' with a lighted splint. Complete the equation for this reaction. K + .....H₂O → 2KOH + .....[1]
(d)(i)When zinc carbonate is warmed in a closed container, an equilibrium mixture is formed. ZnCO₃(s) ⇌ ZnO(s) + CO₂(g) The forward reaction is endothermic. Describe and explain the effect, if any, on the position of equilibrium when the temperature is decreased.[2]
(d)(ii)Describe and explain the effect, if any, on the position of equilibrium when the concentration of carbon dioxide is increased.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

[1] 7(a) high melting point for Ag/ high boiling point for Ag / ORA for K
[1] 7(a) high density for Ag / ORA for K
[1] 7(a) hard for Ag/ soft for K
[1] 7(b) protons: 47
[1] 7(b) neutrons: 62
[1] 7(b) electrons: 46
[1] 7(c) 2K + 2H2O → 2KOH + H2
[1] 7(d)(i) equilibrium moves to the left / less product formed / more reactant formed
[1] 7(d)(i) decreasing temperature pushes the reaction in the direction of releasing energy / decreasing temperature pushes the reaction in the direction of the exothermic reaction
[1] 7(d)(ii) equilibrium moves to the left/less product formed / more reactant formed
[1] 7(d)(ii) reaction goes in the direction to reduce the concentration of carbon dioxide

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