Standard level
Thermal decomposition is the process of breaking a compound apart by heating.
Background
Certain types of compounds thermally dissociate to give predictable products at temperatures easily accessibe in the laboratory.
Metal carbonates (not group 1 metals) decompose to metal oxides, although silver carbonate will decompose all the way to silver.
Decomposition of a divalent metal carbonate
MCO3(s) → MO(s) + CO2(g)
Measuring and recording the initial mass and final mass after heating to constant mass allows us to identify the metal.
Chemicals
- Iron(II) carbonate
- Zinc carbonate
- Magnesium carbonate
- Barium carbonate
- Strontium carbonate
Apparatus
- crucible
- crucible tongs
- heat-proof mats (small)
- oven
- electronic balance
- Approximately 2g of the carbonate is placed in a pre-weighed crucible and the mass recorded
- The crucible is placed on a heat proof mat in the pre-heated oven.
- At 5 minute intervals the crucible is removed from the oven and reweighed.
- The procedure is continued until the mass is constant.
Care must be taken when dealing with hot crucibles. They must not be set down anywhere other than onto a heat-proof mat.