In a TD reaction, a chemical breaks down into more than 1 substance when heated.
- Calcium carbonate decomposes into calcium oxide and carbon dioxide.
- Is used for making glass, cement and limewater.
Equation is: metal carbonate -> metal oxide + carbon dioxide
- The reaction between calcium oxide and water produces calcium hydroxide/slaked lime.
Calcium oxide + water -> calcium hydroxide
CaO (s) + H2O(l) -> Ca(OH2) (s)
- Limewater is calcium hydroxide solution. When limewater reacts with carbon dioxide, a cloudy precipitate of calcium carbonate forms, as it's insoluble.
Calcium hydroxide + carbon dioxide -> calcium carbonate
Ca(OH)2 (aq) + CO2 (g) -> CaCO (s)
Metal Carbonates/ Neutralisation
- Metal carbonates undergo thermal decomposition to metal oxides and carbon dioxide. Some decompose at a lower temperature than others.
- Calcium carbonate decomposes at 825'C. Zinc carbonate at 300'C. Copper carbonate at 200'C.
Zinc oxide (ZnO) used for rubber, concrete, medicine and cosmetics.
Copper oxide (CuO) used for pigments and semiconductors.
Neutral soil/7 is best for growing crops. Acidic soil is made less acidic by mixing it with calcium carbonate, oxide or hydroxide.
Burning coal produces sulfur dioxide that can lead to acid rain. Calcium compounds prevent sulfur dioxide getting to the atmosphere. Calcium oxide neutralises acidic sulfur dioxide to produce calcium sulfate.
CaO (aq) + SO2 (g) -> CaSO3 (s) Calcium sulfate can be sold as it's useful.