Oxides of Carbon

Formation of Carbon Oxides

When carbon burns, it can form different oxides based on how much oxygen is available. Think of it like cooking rice – too little water gives you something different from enough water.

Carbon(IV) Oxide (CO₂) Formation

Carbon(IV) oxide forms when carbon burns in plenty of oxygen. This happens in open air burning where oxygen supply is not restricted. The chemical equation shows this clearly:

C(s) + O₂(g) → CO₂(g)

You see this when charcoal burns completely in your cookstove with good ventilation. The carbon gets enough oxygen to form CO₂. This is the complete combustion of carbon.

Carbon(II) Oxide (CO) Formation

Carbon(II) oxide forms when oxygen supply is limited during burning. This is partial combustion. The equation is:

2C(s) + O₂(g) → 2CO(g)

This dangerous situation happens when you use a generator in a closed room or burn charcoal without proper ventilation. The carbon cannot get enough oxygen to form CO₂, so it forms deadly CO instead.

Comparison of Carbon Oxides

Properties and Chemical Behavior

Carbon(II) Oxide Properties

Carbon(II) oxide is extremely dangerous because it is both colorless and odorless – you cannot detect it with your senses. This is why generator fumes kill people without warning. The gas binds to blood hemoglobin better than oxygen does, preventing oxygen transport in your body.

CO acts as a strong reducing agent. This means it can remove oxygen from metal oxides. For example, it reduces iron oxide to iron in blast furnaces:

Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g)

This property makes CO valuable in metallurgy – the industrial process of extracting metals from their ores.

Carbon(IV) Oxide Properties

Carbon(IV) oxide is the gas you breathe out and the gas plants use for photosynthesis. At normal atmospheric levels (about 0.04%), it is harmless. However, high concentrations can cause suffocation because it displaces oxygen.

When CO₂ dissolves in water, it forms a weak acid called carbonic acid:

CO₂(g) + H₂O(l) ⇌ H₂CO₃(aq)

This is why rainwater is naturally slightly acidic, and why soft drinks taste slightly sour when carbonated.

Natural and Industrial Sources

Natural Sources

Both oxides occur naturally, though CO₂ is far more common:

• Respiration: All living things produce CO₂ when breathing
• Volcanic activity: Volcanoes release both CO and CO₂
• Forest fires: Produce CO when combustion is incomplete
• Ocean release: Oceans absorb and release CO₂
• Decay of organic matter: Dead plants and animals release CO₂

Industrial Sources

Human activities produce large amounts of both oxides:

• Vehicle exhaust: Cars and generators produce CO (incomplete combustion) and CO₂
• Industrial furnaces: Metal extraction produces both gases
• Power generation: Burning fossil fuels in power stations
• Fermentation: Breweries and bakeries release CO₂
• Cement production: Heating limestone releases CO₂

Environmental and Health Impact

Carbon(II) Oxide Dangers

CO poisoning kills many Nigerians yearly, especially during harmattan when people close windows and doors tightly. Common danger situations include:

• Running generators in closed spaces (garages, corridors)
• Using charcoal stoves in poorly ventilated rooms
• Sitting in cars with engines running in closed garages
• Faulty gas appliances in homes

Symptoms of CO poisoning include headache, dizziness, weakness, nausea, and confusion. Severe exposure leads to unconsciousness and death.

Carbon(IV) Oxide and Climate

CO₂ is a greenhouse gas that traps heat in Earth’s atmosphere. While not poisonous at normal levels, increasing CO₂ from burning fossil fuels contributes to global warming. This affects weather patterns, causing more severe droughts and floods in Nigeria.

Common WAEC Exam Mistakes

WAEC Chief Examiners report these common errors:

• Confusing CO and CO₂: Students write “carbon dioxide” when they mean “carbon monoxide” and vice versa. Always check the Roman numerals.
• Wrong oxygen numbers: Writing that CO has two oxygen atoms or CO₂ has one. Carbon(II) oxide has one oxygen; Carbon(IV) oxide has two.
• Incomplete equations: Forgetting state symbols or not balancing equations properly.
• Toxicity confusion: Stating that CO₂ is toxic or that CO is harmless. CO is the deadly one.
• Poor explanation of formation: Just mentioning “combustion” without specifying whether oxygen supply is limited or sufficient.
• Cannot distinguish “state” from “explain”: When asked to state formation conditions, students write long explanations instead of brief points.

Practice Questions

Multiple Choice Questions

1. Which of the following is produced when carbon burns in limited supply of oxygen?
a) Carbon(IV) oxide
b) Carbon(II) oxide ✓
c) Carbon(III) oxide
d) Carbon dioxide and water

2. The oxide of carbon that turns limewater milky is:
a) CO
b) CO₂ ✓
c) Both CO and CO₂
d) Neither CO nor CO₂

3. Which statement about carbon(II) oxide is correct?
a) It is heavier than air
b) It supports combustion
c) It is a strong reducing agent ✓
d) It dissolves in water to form an acid

4. Carbon(IV) oxide is produced industrially by:
a) Heating carbon in absence of air
b) Fermentation of sugar solutions ✓
c) Electrolysis of water
d) Reduction of metal oxides

Essay Questions

1. (a) State three differences between carbon(II) oxide and carbon(IV) oxide. (3 marks)
(b) Explain why carbon(II) oxide is dangerous in enclosed spaces. (3 marks)
(c) Write balanced equations for the formation of each oxide from carbon. (4 marks)

Examiner’s tip: For part (a), use a comparison format. For (b), explain the binding to hemoglobin and colorless/odorless nature. For (c), include state symbols.

2. (a) Describe how carbon(IV) oxide is formed during respiration. (3 marks)
(b) State four natural sources of carbon(IV) oxide. (4 marks)
(c) Explain the role of carbon(II) oxide in the extraction of iron from its ore. (3 marks)

Examiner’s tip: In (c), write the equation and explain reduction process. Don’t just mention “it removes oxygen.”

3. (a) Distinguish between complete and incomplete combustion of carbon. (4 marks)
(b) State three physical properties of carbon(IV) oxide. (3 marks)
(c) Why does carbon(IV) oxide not support burning? (3 marks)

Examiner’s tip: “Distinguish” means show clear differences, not just describe each one separately.

Memory Aids

Remember oxide formation:
“SLIP” – Scarce oxygen → Limited combustion → Incomplete burning → Poisonous CO

Remember CO₂ vs CO:
“TWO is SAFE, ONE is DONE” – CO₂ (two oxygens) is safe; CO (one oxygen) can be deadly

For uses:
“FIRED”
Fire extinguishers (CO₂)
Iron extraction (CO)
Refrigeration (CO₂)
Effervescence in drinks (CO₂)
Dry ice (CO₂)

Related Topics

Understanding oxides of carbon connects to several other chemistry topics:

• Carbon(II) Oxide [CO] – Detailed study of carbon monoxide properties and uses
• Physical Properties of CO₂ – Comprehensive look at carbon dioxide characteristics
• Chemical Properties of CO₂ – Reactions and chemical behavior of CO₂
• Laboratory Preparation of CO₂ – How to produce CO₂ in the lab
• Test for CO₂ – Laboratory methods to identify carbon dioxide