Reactions of calcium oxide, hydroxide, carbonate and

bicarbonate.

Reactions of calcium carbonate.

Calcium carbonate decomposes when heated…

… forming calcium oxide.

CaCO3 → CaO + CO2

Manufacture of lime

Limestone was traditionally burnt in small lime kilns.

Reactions of calcium oxide (“quick lime”)

Calcium hydroxide reacts vigorously with water to give

calcium hydroxide.

CaO + H2O →Ca(OH)2

The resulting solution has a

pH of 9 - 11

• During the Black Death corpses were buried with quicklime.

• By reacting with moisture from the bodies it prevent the spread of the disease.

Reactions of calcium hydroxide

Ca(OH)2 neutralises acids.

Ca(OH)2 + 2HCl→ CaCl2 + 2H2O

It is commonly known as “slaked lime” and is used by farmers to lower soil acidity. It is also used in some anti acids.

Reaction of limewater with carbon dioxide.

When carbon dioxide is passed through limewater

it turns milky due to the formation of

insoluble calcium carbonate.

Ca(OH)2 + CO2→ CaCO3 + H2O

This is the standard test for carbon dioxide.

Red blood cells and carbon dioxide transport

CO2 + H2O → H2CO3

This reaction is speeded up by carbonic anhydrase, an enzyme found in red blood cells.

Carbon dioxide dissolves to form carbonic acid

• Carbonic acid then dissociates;• H2CO3 ⇌ H+ + HCO3

-

• The bicarbonate passes out of the red blood cell, to be replaced by chloride ions.

• The proton is taken by haemoglobin, to buffer blood.

• To do this it must give up its oxygen.• HbO2 → Hb + O2

• Hb + H+ ⇌ HHb• The opposite happens in the lungs.

Expired air; 0.4 % CO2

Inspired air: 0.004% CO2

Reaction of limewater

If excess carbon dioxide is passed through lime water the carbonate will disappear…

… forming a colourless solution of bicarbonate.

CaCO3 + H2O + CO2 → Ca(HCO3)2

Hard waterIn limestone regions water contains relatively high amounts of calcium (and magnesium) bicarbonate.

Calcium ions react with detergents to make a scum rather than a lather.

Waters high in bicarbonates are therefore said to be hard.

Calcium bicarbonate is unstable, decomposing on heating to produce insoluble calcium carbonate.

Ca(HCO3)2 → CaCO3+H2O + CO2

Depositing lime scale on the elements of kettles.