Reactions of calcium oxide, hydroxide, carbonate and bicarbonate.

Reactions of calcium carbonate. Calcium carbonate decomposes when heated… … forming calcium oxide. CaCO 3 → CaO + CO 2

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 + H 2 O →Ca(OH) 2 The resulting solution has a pH of

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→ CaCl 2 + 2H 2 O 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 + CO 2 → CaCO 3 + H 2 O This is the standard test for carbon dioxide.

Red blood cells and carbon dioxide transport CO 2 + H 2 O → H 2 CO 3 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; H 2 CO 3 ⇌ H + + HCO 3 - 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. HbO 2 → Hb + O 2 Hb + H + ⇌ HHb The opposite happens in the lungs.

Expired air; 0.4 % CO 2 Inspired air: 0.004% CO 2

Reaction of limewater If excess carbon dioxide is passed through lime water the carbonate will disappear… … forming a colourless solution of bicarbonate. CaCO 3 + H 2 O + CO 2 → Ca(HCO 3 ) 2

Hard water In 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(HCO 3 ) 2 → CaCO 3 +H 2 O + CO 2 Depositing lime scale on the elements of kettles.