Chemistry · Oct / Nov 2022 · Paper 42 · Question 2
0620
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Sodium is a reactive metal.
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2(a)[1]
to prevent contact with air / oxygen and / or water
2(b)(i)[1]
combustion
2(b)(ii)[1]
yellow
2(b)(iii)[2]
4Na + O2 → 2Na2O
M1 species (1)
M2 balancing (1)
2(b)(iv)[3]
M1 eight crosses in second shell of both Na (1)
M2 six dots and two crosses in second shell of O (1)
M3 ‘+’ charge on each Na ion on correct answer line and ‘2–‘ charge on O ion on correct answer line (1)
2(c)(i)[1]
proton acceptor
2(c)(ii)[1]
pH 14
2(c)(iii)[1]
yellow
2(c)(iv)[5]
M1 mol Na = 0.345 / 23 = 0.015(00) (1)
M2 mol NaOH = M1 = 0.015(00) (1)
M3 M2 × 1000 / 50 = 0.015(00) × 20 = 0.3(00) (1)
M4 Mr NaOH = 40(1)
M5 M4 × M3 = 40 x 0.3= 12.(0) (g / dm3) (1)
2(d)(i)[1]
precipitation
2(d)(ii)[1]
red-brown
2(d)(iii)[1]
iron(III) hydroxide
2(d)(iv)[3]
Fe3+(aq) + 3OH–(aq) → Fe(OH)3(s)
M1 Fe(OH)3 (as only product) (1)
M2 Fe3+ and 3OH– (as only reactants) (1)
M3 state symbols (1)
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