Carbon (II) oxide notes for secondary schools


Laboratory preparation

  1. Dehydration of methanoic acid using concentrated sulphuric (VI) acid

HCOOH (s) → CO (g) + H2O (l)

  1. If sodium methanoate is used it is first converted to methanoic acid

HCOOH (s) + H2SO4 (l) → HCOOH (l) + NaHSO4(s)

Methanoic acid produced is then dehydrated to carbon (II) oxide.

  1. Dehydration of ethanedioic acid (oxalic acid)

H2C2O4 (s) → CO (g) + CO2 (g) + H2O (l)

The reaction also produces carbon (IV) oxide therefore the gas produced is passed through concentrated sodium hydroxide or concentrated potassium hydroxide to remove carbon (IV) oxide.

  1. Another method is passing carbon (IV) oxide through heated charcoal

A stream of carbon (IV) oxide is passed over strongly heated charcoal

C (s) + CO2 (g) → 2CO (g)

Any unreacted CO2 (g) is absorbed in potash solution (potassium hydroxide solution)

2KOH (aq) + CO2 (g) → K2CO3 (aq) + H2O (l)


Physical properties

  • Colourless and odourless
  • Almost insoluble in water
  • Poisonous
  • Slightly less denser than air
  • No effect on wet litmus paper – it’s neutral

Chemical properties

Reaction with oxygen

Burn in air with a pale blue flame forming carbon (IV) oxide

2CO (g) + O2 (g) → 2CO2 (g)

The gas produced forms a white precipitate with lime water hence this is a test for carbon (II) oxide

Test for Carbon (II) oxide

The gas is burnt in air and the gas produced bubbled through lime water. Formation of white precipitate indicates presence of carbon (II) oxide.

Reducing property

It reduces metal oxides of some elements like zinc, iron, lead and copper

Dry copper (II) oxide is reduced to copper while carbon (II) oxide is oxidized to carbon (IV) oxide.

CO (g) + CuO (s) → Cu (s) + CO2 (g)

PbO (s) + CO (g) → Pb (s) + CO2 (g)

ZnO (s) + CO (g) → Zn (s) + CO2 (g)

Fe2O3 (s) + 3CO (g) → 2Fe (s) + 3CO2 (g)

Note: Carbon (II) oxide is a very poisonous gas it combines with haemoglobin of the red blood cells forming a stable compound carboxyhaemoglobin which does not release its carbon (II) oxide in the tissues the way oxyhaemoglobin releases its oxygen hence the person dies slowly due to lack of oxygen

The gas lacks colour, smell or taste, thus breathed unnoticed making it extremely dangerous.

Burning charcoal stove

  • At region A there is plenty of air and carbon burns completely forming carbon (IV) oxide

C (s) + O 2 (g) → CO2 (g)

  • At region B there is insufficient supply of air and carbon (IV) oxide formed at region A is reduced to carbon (II) oxide

CO 2 (g) + C (s) → 2CO (g)

  • At region C carbon (II) oxide formed at region B burns with a pale blue flame forming Carbon (IV) oxide

2CO (g) + O 2 (g) → 2CO2 (g)

If plenty of air is available at the top all carbon (II) oxide burns forming carbon (IV) oxide, however if there is insufficient air then CO escapes into the atmosphere, hence it is advisable to open all windows and doors when using a charcoal stove

Exhaust fumes from cars contain a considerable amount of carbon (II) oxide due to incomplete combustion of petrol

Uses of carbon (II) oxide

As a fuel since when it burns it produces a harmless gas

Reducing agent in extraction of metals

Manufacture of synthetic petrol

Here are some useful links


carbon (IV) oxide

Solvay process

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