Carbon (IV) oxide notes for secondary schools



0.03% of atmosphere by volume

Respiration from both plants and animals

Combustion of fuels such as petrol, coal and wood

Laboratory preparation

  1. Reaction between marble chips (calcium carbonate) and dilute hydrochloric acid.

Set the apparatus as shown below.

preparation of carbon (IV) oxide

Open the tap of the thistle funnel and let the acid to cover the marble chips.

Do not collect the first few bubbles of the gas since it contains a mixture of air and carbon (IV) oxide

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H 2O (l)

  • Water absorbs any traces of hydrogen chloride gas carried with the gas.
  • Concentrated sulphuric (VI) acid dries the gas
  • The gas is collected by downward delivery since it’s denser than air.

NOTE: Dilute sulphuric (VI) acid reacts with marble chips producing insoluble salt of calcium sulphate which coats the rest of the carbonate hence the reaction stops almost immediately.

  1. Action of heat on carbonates and hydrogen carbonates

ZnCO3 (s) → ZnO (s) + CO2 (g)

2NaHCO3 (s) → Na2CO3 (s) + H2O (l) + CO2 (g)


Physical properties

  • Colorless and odorless
  • Extinguishes a burning splint
  • Slightly soluble in water
  • Denser than air hence collected by downward delivery
  • Acidic (turns wet blue litmus to red)

Chemical properties

Reaction with burning magnesium

When burning magnesium is inserted in a gas jar of carbon (IV) oxide it continues to burn

A white ash of magnesium oxide is formed and a black solid of carbon

2Mg (g) + CO2 (g) → 2MgO (s) + C (s)

  • The reaction takes place because when magnesium burns it produces high temperature which decomposes carbon (IV) oxide forming carbon and oxygen thus continues to burn in the oxygen produced.
  • Magnesium is more reactive than carbon

Action on water

Carbon (IV) oxide slightly dissolves in water forming weak carbonic acid

CO2 (g) + H2O (l) → H2CO3 (aq)

Action on alkalis

Carbon (IV) oxide is more soluble in alkalis than in water since it is an acid gas forming carbonates

  1. Reaction with lime water.


When passed through lime water a white precipitate of calcium carbonate is formed

Ca (OH) 2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l)

The precipitate dissolves if carbon (IV) oxide is dissolved in excess this is because white calcium carbonate reacts with excess carbon (IV) oxide forming a soluble calcium hydrogen carbonate

CaCO3 (s) + H2O (l) + CO2 (g) → Ca (HCO3)2 (aq)

  1. Reaction with sodium hydroxide.

CO2 (g) + 2NaOH (aq) → H2O (l) + Na2CO3 (aq)

In excess carbon (IV) oxide sodium hydrogen carbonate is formed

CO2 (g) + H2O (l) + Na2CO3 (aq) → 2NaHCO3 (s)


  • Manufacture of aerated drinks
  • As a refrigerant due to the fact that It is a better coolant than ordinary ice and It sublimes without leaving any wetness.
  • In fire extinguishers because:
  • It is denser than air hence covers the flame and cuts off oxygen supply.
  • Extinguishes fire.
  • Cloud seeding – small pieces of dry ice are dropped into the clouds which causes rapid cooling causing rain to fall during drought or in areas with little rain

You can move to

carbon (II) oxide


Solvay process


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