Chemistry · May / June 2025 · Paper 41 · Question 4
0620
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The question as text
This question is about nitrogen and its compounds. Nitrogen contains molecules with the formula N2.
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4(a)[2]
M1 3 dots and 3 crosses shared
M2 one non-bonding pair of 2 dots on one N atom and 2 crosses on the other N atom to complete the octet on both
4(b)(i)[3]
Conditions can be in any order
M1 (temperature) 450 and °C
M2(pressure)
200 and atmospheres / 20 000 and kPa
M3 iron and catalyst
N2 + 3H2 ⇌ 2NH3
4(b)(ii)[1]
The answer is a drawing: see the picture of this mark scheme row.
4(c)(i)[1]
5O2 → 4NO + 6H2O
M1 –3
4(c)(ii)[2]
M2 +2
4(c)(iii)[1]
increase in oxidation number
4(c)(iv)[2]
4NO + 3O2 + 2H2O → 4HNO3
M1 HNO3(1)
M2 equation completely correct
4(d)[3]
M1 15
M2 7.5
M3 990
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