C3.23 Thermal decomposition of calcium carbonate
calcium carbonate ---heat---> calcium oxide + carbon dioxide
CaCO3(s) ---heat---> CaO(s) +CO2(g)
(limestone)
(quicklime)
C3.24 Water and calcium oxide
calcium oxide + water ---> calcium hydroxide
CaO(s) + H2O(l) ---> Ca(OH)2(s)
(slaked lime) looks flaky and gets hot
With more water the calcium hydroxide dissolves to make limewater Ca(OH)2(aq)
C3.25 Neutralising soil acidity
Calcium oxide and calcium hydroxide are bases. (like all metal oxides and
hydroxides)
acid + base ---> salt + water
so acid soil is neutralised by calcium oxide or calcium hydroxide
e.g. nitric acid + calcium oxide --> calcium nitrate + water
2HNO3(aq) + CaO(s) ---> Ca(NO3)2(aq) +H2O(l)
Farmers can add calcium oxide or calcium hydroxide to their acid soil to
neutralise it.
The neutral soil is better for growing plants.
Task C3.25 Write word equations and balanced
chemical equations for neutralising the following acids using calcium oxide and
calcium hydroxide: nitric acid, sulphuric acid, hydrochloric acid, phosphoric
acid (H3PO4)
C3.26 Uses of calcium carbonate
Cement is made from calcium carbonate (limestone).
limestone --heat--> calcium oxide + carbon dioxide
Calcium oxide + clay ----> cement
Glass is made using calcium carbonate.
Calcium carbonate + sand + sodium carbonate ---heat--> glass
Iron is manufactured using calcium carbonate in the blast furnace.
calcium carbonate --heat--> calcium oxide + carbon dioxide
Calcium oxide + silicon dioxide ----> calcium silicate
(mostly sand) (slag)
(floats on top of molten iron)