O-LevelChemistryMetals & Reactivity5070/21 · May/June 2023 · Q28 Marks

Group I includes the elements lithium, sodium and potassium.

(a)State two physical properties of lithium. 1 2[2]
(b)(i)Potassium reacts with cold water. The ionic equation for the reaction is shown. 2K(s) + 2H2O(1) → 2K+(aq) + 2OH¯(aq) + H2(g) State, in terms of electrons, why potassium is a reducing agent in this reaction.[1]
(b)(ii)State the oxidation number of hydrogen in H2.[1]
(b)(iii)Describe what is observed during this reaction.[3]
(c)A sample of sodium chloride is tested using a flame test. State the colour of the flame seen in this test.[1]

Mark scheme

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

2(a) Any two from: soft (1) low density / floats on water (1) low melting point (1) good thermal conductor / conducts heat (1) good electrical conductor / conducts electricity (1) lustrous / shiny (when freshly cut) (1) ductile (1) malleable (1)
2(b)(i) potassium loses electrons
2(b)(ii) 0 (1)
2(b)(iii) Any three from: (potassium) floats on water/moves across the surface of water (1) (potassium) melts (1) bubbles / fizzes / effervesces (1) forms a colourless solution / piece gets smaller and smaller (1) lilac flame (1)
2(c) yellow / orange (1)

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