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Chemistry - Chemical reactions - Decomposition reactions

Terms in this set (11)

- The reaction that occurs when both calcium carbonate and calcium hydroxide are heated is thermal decomposition because heat was applied to both calcium carbonate and calcium hydroxide, both broke down into smaller, simpler species
- When calcium carbonate a white powder is heated over a bunsen burner, another white solid of calcium oxide would form, as well as a colourless gas of carbon dioxide will be given off. To test for the presence of carbon dioxide limewater can be used. Bubble the gas through limewater and if the limewater turns milky white then carbon dioxide is present and has been produced.
- When calcium hydroxide a white solid is heated another white solid of calcium oxide would form as well as a colourless vapour that may condense on the sides of the test tube. This vapour produced is water that can be identified by using blue cobalt chloride paper which will go from blue to pink if water is produced.
- When both calcium carbonate and calcium hydroxide are heated a white solid of calcium oxide is produced because calcium oxide is a smaller, simpler of both calcium carbonate and calcium hydroxide
- But, the gases produced by heating calcium carbonate and calcium hydroxide are different as calcium carbonate releases carbon dioxide which will turn limewater milky white and calcium hydroxide will produce water which will turn blue cobalt chloride paper pink

Balanced symbol equation for heating of calcium carbonate
CaCO3 ---> CaO + CO2

Balanced symbol equation for the heating of calcium hydroxide
Ca(OH)2 ---> CaO + H2O
Lead hydroxide
- Upon heating lead hydroxide, water and lead oxide will be formed. Condensation will occur on the coldest parts of the test tube. The water vapour turn blue cobalt chloride paper pink confirming the presence of water. The decomposition of lead hydroxide only produces a white solid of lead oxide, and water vapour and therefore can be identified. Limewater will remain colourless when vapour is passed through
- After heating sodium hydrogen carbonate it will produce sodium carbonate a white solid, carbon dioxide a colourless gas and water vapour will be formed. The colourless water vapour will turn blue cobalt chloride paper pink which will confirm the presence of water. The carbon dioxide will turn limewater milky white by producing insoluble calcium carbonate
- Upon heating calcium carbonate, a white solid of calcium oxide and a colourless gas of carbon dioxide will be produced. The carbon dioxide produced will turn limewater milky white and this will confirm the presence of carbon dioxide
- Therefore these solids can be identified by thermal decomposition reactions and cobalt chloride paper and limewater test to confirm the presence of the products produced. The solid which has a decomposition reaction that is positive for cobalt chloride but negative for limewater is lead hydroxide. The solid which upon heating produces positive results for both test if sodium hydrogen carbonate. The solid which produces negative test for cobalt chloride paper but a positive test for limewater is calcium carbonate

Balanced symbol equations
Ph(OH)2 ---> PbO + H2O
2NaHCO3 ---> Na2CO3 + H2O + CO2
CaCO3 ---> CaO + CO2

(Lime water)
Ca(OH)2 + CO2 ---> CaCO3 + H2O
CaCO3 + H2O + CO2 ---> Ca(HCO3)2