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AS · Practice questions · Nitrogen, ammonia and the ammonium ion

From air to fertiliser.

Six original Cambridge-style questions on nitrogen, ammonia and the ammonium ion.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
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Lone pair accepts the proton.

01
Explain
[2 marks]

Explain why nitrogen is very unreactive.

  • The N≡N triple bond is very strong (944 kJ mol−1), so a lot of energy is needed to break it. ✓
  • The molecule is non-polar, so it does not attract electrophiles or nucleophiles. ✓
02
Explain
[3 marks]

Describe, with an equation, how ammonia behaves as a base, and explain the change in bond angle.

  • NH3 + H+ → NH4+; the nitrogen lone pair forms a dative bond to H+. ✓
  • NH3: 3 bonding pairs + 1 lone pair, 107°. ✓
  • NH4+: 4 bonding pairs, no lone pairs, so the repulsions are equal: 109.5°. ✓
03
Recall
[2 marks]

Write an equation for the reaction of ammonium sulfate with sodium hydroxide, and describe a test for the gas produced.

  • (NH4)2SO4 + 2NaOH → Na2SO4 + 2NH3 + 2H2O. ✓
  • Ammonia turns damp red litmus paper blue. ✓
04
Calculation
[2 marks]

Calculate the percentage by mass of nitrogen in ammonium nitrate, NH4NO3.

  • Mr = 14.0 + 4.0 + 14.0 + 48.0 = 80.0. ✓
  • %N = 28.0 ÷ 80.0 × 100 = 35.0%. ✓
05
Calculation
[2 marks]

A farmer needs 70.0 kg of nitrogen. Calculate the mass of urea, CO(NH2)2 (Mr 60.0), required.

  • Urea is 28.0 ÷ 60.0 = 46.7% nitrogen. ✓
  • Mass = 70.0 ÷ 0.467 = 150 kg. ✓
06
Explain
[2 marks]

Explain why farmers should not add calcium hydroxide to soil at the same time as an ammonium fertiliser.

  • Ca(OH)2 is a base, which reacts with ammonium ions: NH4+ + OH− → NH3 + H2O. ✓
  • Nitrogen is lost as ammonia gas, so the fertiliser is wasted. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.