12.1 nitrogen and sulfur

Explain the lack of reactivity of nitrogen

• the two nitrogen atoms are joined by a very strong triple bond

• This bond has a very high bond enthalpy, meaning a large amount of energy is required to break it.

• NN molecule is non-polar because the 2 atoms have the same electronegativity

describe and explain the basicity of ammonia

• ammonia has a lone pair of electrons which can accept the proton on the N2 atom to form an ammonium ion.

• NH₃ (aq) + H₂O (l) ⇌  NH₄⁺ (aq) + OH^- (aq)

• Position of eq lies to left, ammonia sol is weakly alkaline

describe and explain the structure of the ammonium ion and its formation by an acid base reaction

NH₃ (aq) + H₂O (l) ⇌  NH₄⁺ (aq) + OH^- (aq)

Ammonia: trigonal pyramidal

Ammonium ion: tetrahedral as ammonia uses lone pair to form a dative covalent bond with proton

Describe and explain the displacement of ammonia from ammonium salt by an acid base reaction.

React ammonium salt with base to test for ammonium ions

Ammonia is given off and turns litmus paper blue

Define primary pollutant:

Pollutants given off directly from the source of pollution

Define secondary pollutants

Pollutants that are not given of directly into the air from human activity

How is PAN formed

When nitrogen oxides in the air react with VOCS

State an example of a primary pollutant

• Nitrogen oxide found in lightning

• VOCS: unburnt hydrogen carbons from fuel and the oxidised products in exhaust fumes

State the two secondary pollutant types

• PAN

• Photochemical reactionS between nitrogen oxides and VOCS

Explain how acid rain occurs

• nitrogen (II) oxide is formed in lightning strikes.

• It is oxidised to form nitrogen (IV) oxide in air

• 2NO(g) + O2 → 2NO2 (g)

• Further oxidation to nitric acid when nitrogen (IV) oxide dissolves and reacts in water

2NO2 + 2H2O + 3O2 → 4HNO3

How is sulfuric acid formed?

• Sulfur(IV) oxide (SO₂) is another pollutant found in the atmosphere

• When SO₂ is oxidised, it forms SO₃ which reacts with rainwater to form dilute sulfuric acid:

SO₃ (g) + H₂O (l) → H₂SO₄ (aq)

• Nitrogen oxides can also act as catalysts in the formation of acid rain

• NO₂ catalyses the oxidation of SO₂ to SO₃:

• NO₂ (g) + SO₂ (g) → SO₃ (g) + NO (g)

  • The formed NO gets oxidised to regenerate NO₂:

  NO (g) + ½ O₂ (g) → NO₂ (g)

  • The regenerated NO₂ molecule can get again oxidise another SO₂ molecule to SO₃ which will react with rainwater to form H₂SO₄

Define PAN

A component of photochemical smog: when volatile organic compounds (VOCs) react in sunlight

How can we reduce the effects of nitrogen oxides?

Car exhaust systems fitted with catalytic converters to help reduce pollutants from motor vehicles.

Pollutant gases react on surface of hot catalyst Pt and nitrogen oxides reduced to harmless N2 gas.

2CO + 2NO → 2CO2 + N2