CARBON (IV) OXIDE
0.03% of atmosphere by volume
Respiration from both plants and animals
Combustion of fuels such as petrol, coal and wood
- Reaction between marble chips (calcium carbonate) and dilute hydrochloric acid.
Set the apparatus as shown below.
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.
- Action of heat on carbonates and hydrogen carbonates
ZnCO3 (s) → ZnO (s) + CO2 (g)
2NaHCO3 (s) → Na2CO3 (s) + H2O (l) + CO2 (g)
- 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)
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
- 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)
- 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
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