Chemistry · May / June 2021 · Paper 42 · Question 5
0620
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This question is about compounds of nitrogen.
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5(a)(i)[2]
6Li + N2 → 2Li3N
N2 as reactant (1)
rest of equation (1)
5(a)(ii)[2]
new octet of 8 electrons consisting of 5 crosses and 3 dots in second shell (1)
charge of 3– (1)
5(b)(i)[3]
bonds broken [945 + (3 × 160)] = 1425 (1)
bonds formed (2 × 3 × 300) = 1800 (1)
energy change = M1 – M2 = 1425 – 1800 = –375 (1)
5(b)(ii)[1]
Answer must reflect answer in 5(b)(i)
exothermic
and
more energy released (in bond formation) than used/taken in (in bond breaking)
5(b)(iii)[3]
N with 1 bonding pair with each F (1)
2 non-bonding dots for N (1)
6 non-bonding crosses for F (1)
5(c)[3]
ionic bonds in Li3N (1)
attraction between molecules in NF3 (1)
weaker attraction (between particles) in NF3 ORA (1)
5(d)(i)[2]
rfm of NH4NO3 = 80 (1)
mass of N = 2 × 14 = 28 and percentage N = 100 × 28 / 80 = 35% (1)
5(d)(ii)[1]
fertiliser
5(d)(iii)[1]
calcium hydroxide
5(e)(i)[1]
7 < × ⩽ 11
proton acceptor
5(e)(ii)[1]
The answer is a drawing: see the picture of this mark scheme row.
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