4.2.3Organic Chemistry
Nitrogen Oxides and Sulfur Dioxide — Edexcel International GCSE Science Double Award 4SD0 - Chemistry Revision Notes & Topical Questions
5 min read 12 parts Lesson 7 of 24
Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
Section 1 of 12Where nitrogen oxides come from
High temperature reactions
- High temperature reactions Nitrogen and oxygen from the air do not normally react.
- In the very high temperatures and pressures inside car engines and blast furnaces they combine to form nitrogen monoxide, NO,
- and nitrogen dioxide, NO2.
Lightning
- Lightning Lightning also supplies enough energy to make nitrogen oxides in the atmosphere, so they are not entirely man-made.
Other exhaust gases
- Other exhaust gases Exhaust also contains carbon monoxide and unburnt hydrocarbons, which are harmful too.
Section 2 of 12Where sulfur dioxide comes from
1Impure fuel
- Impure fuel Coal, crude oil and other fossil fuels contain small amounts of sulfur impurities.
2Burning the fuel
- Burning the fuel When the fuel burns, the sulfur is oxidised.
3Sulfur dioxide made
- Sulfur dioxide made S(s) + O2(g) → SO2(g)
4Released to the air
- Released to the air The gas escapes with the waste gases from power stations and engines and travels into the atmosphere.
Section 3 of 12How acid rain forms
1
Sulfur dioxide dissolves in water droplets in clouds and reacts with oxygen to give sulfuric acid: 2SO2(g) + O2(g) + 2H2O(l) → 2H2SO4(aq).
2
Nitrogen dioxide reacts with water to make a mixture of nitrous and nitric acids: 2NO2(g) + H2O(l) → HNO2(aq) + HNO3(aq).
3
With extra oxygen, nitrogen dioxide forms nitric acid alone: 4NO2(g) + 2H2O(l) + O2(g) → 4HNO3(aq).
4
The droplets in the cloud grow larger as they collect more acid and water.
5
When they are heavy enough, they fall as acid rain.
Section 4 of 12Harmful effects
| Pollutant | Main problems caused |
|---|---|
| Sulfur dioxide | Acid rain; irritates lungs, throat and eyes |
| Nitrogen oxides | Acid rain; photochemical smog; breathing difficulties, especially for people with asthma |
| Acid rain | Corrodes metal structures and damages buildings and statues made of limestone or marble; harms fish and other aquatic life; damages crops and pollutes water supplies |
Section 5 of 12Reducing the pollution
Cutting emissions
Catalytic converters
- Catalytic converters Fitted in car exhaust systems, they use a catalyst to turn harmful gases into harmless ones: nitrogen oxides become nitrogen, carbon monoxide becomes carbon dioxide and hydrocarbons are oxidised.
Cleaner fuels
- Cleaner fuels Removing sulfur from fuels before burning stops sulfur dioxide forming in the first place.
Removing gases at power stations
- Removing gases at power stations Waste gases can be passed through alkaline substances which absorb sulfur dioxide before release.
Section 6 of 12Sources and Formation
1
In engines and furnaces, the high temperature and pressure cause nitrogen and oxygen from the air to react, forming nitrogen monoxide: N₂ + O₂ → 2NO.
2
Nitrogen monoxide is then oxidised by more oxygen in the air to form nitrogen dioxide, NO₂.
3
Fossil fuels contain sulfur impurities, which are oxidised during combustion to form sulfur dioxide: S + O₂ → SO₂.
4
Catalytic converters in car exhausts help to reduce the amount of harmful gases released to the atmosphere.
Section 7 of 12How Acid Rain Forms
How Acid Rain Forms
From sulfur dioxide
- From sulfur dioxide SO₂ dissolves in rainwater and is oxidised to sulfuric acid: 2SO₂ + O₂ + 2H₂O → 2H₂SO₄.
From nitrogen dioxide
- From nitrogen dioxide NO₂ reacts with rainwater to form a mixture of nitrous and nitric acids: 2NO₂ + H₂O → HNO₂ + HNO₃.
From lightning
- From lightning Lightning can produce nitrogen oxides in air, which form nitric acid with rain and oxygen: 4NO₂ + 2H₂O + O₂ → 4HNO₃.
Falling as rain
- Falling as rain The acidic droplets grow as clouds rise and cool, and they fall as acid rain when they are heavy enough.
Section 8 of 12Effects on People and the Environment
Corrosion
- Corrosion Acid rain attacks metal structures and buildings or statues made of carbonate rocks such as limestone.
Aquatic life
- Aquatic life Acidified lakes and rivers can harm fish and other aquatic organisms.
Crops and water
- Crops and water Acid rain can damage crops and contaminate water supplies.
Smog
- Smog Nitrogen oxides contribute to photochemical smog, which can cause breathing difficulties.
Breathing
- Breathing Sulfur dioxide irritates the lungs, throat and eyes, and the effects are worse for people with asthma.
Section 9 of 12Worked Example
Question Using the equation 2SO₂ + O₂ + 2H₂O → 2H₂SO₄, calculate how many moles of sulfuric acid form from 4 moles of sulfur dioxide.
- The equation shows 2 mol SO₂ gives 2 mol H₂SO₄, a 1:1 ratio
- 4 mol SO₂ therefore gives 4 mol H₂SO₄
Answer 4 mol of sulfuric acid.
Section 10 of 12Exam Checklist & Tips
4.2.3 – Key Points for the Exam
- Acid rain Rain made acidic by dissolved sulfur dioxide and nitrogen oxides.
- Nitrogen oxides (NOₓ) Gases such as NO and NO₂ formed when nitrogen and oxygen react at high temperature.
- Photochemical smog Air pollution containing ozone and other irritants, formed in sunlight from nitrogen oxides.
- Catalytic converter A device in a car exhaust that converts harmful gases into less harmful substances.
- Sulfuric acid A strong acid, H₂SO₄, formed when sulfur dioxide dissolves in rainwater and is oxidised.
Common Mistakes
- Blaming carbon dioxide as the main cause of acid rain; the main acids come from SO₂ and nitrogen oxides.
- Writing the acid rain equation for SO₂ without the oxygen and water that are needed.
- Forgetting that nitrogen and oxygen react to form NO only at the high temperatures in engines and furnaces.
- Describing catalytic converters as removing all pollutants, when they only reduce harmful gases.
Section 11 of 12Key terms
| Term | Meaning |
|---|---|
| Acid rain | Rainwater made more acidic by dissolved sulfur and nitrogen oxides. |
| Catalytic converter | A device in a car exhaust containing a catalyst that converts harmful gases to less harmful ones. |
| Photochemical smog | A haze of pollutants formed when sunlight acts on nitrogen oxides and other gases. |
| Fossil fuel | A fuel such as coal, oil or gas formed from ancient organisms. |
| Oxidation | A reaction in which a substance gains oxygen. |
Section 12 of 12Exam technique
1
Saying nitrogen oxides come from the fuel. They form from nitrogen and oxygen in the air at high temperatures.
2
Confusing the sourcessulfur dioxide comes from sulfur impurities in fuels, not from the air.
3
Stating that carbon dioxide causes acid rain. The main causes are sulfur dioxide and nitrogen oxides.
4
Forgetting that catalytic converters change gases into harmless ones, rather than filtering or storing them.
5
Writing the acid formed from sulfur dioxide as sulfurous acid when the equation here gives sulfuric acid, H2SO4.
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