Passage III

As calcium oxalate hydrate (CaC₂O₄·H₂O) is heated, it first dehydrates to yield calcium oxalate (CaC₂O₄). Next, the CaC₂O₄ decomposes into calcium carbonate (CaCO₃) and carbon monoxide (CO). The CaCO₃ then further decomposes into CaO and CO₂ (see equations below).

CaC₂O₄·H₂O(solid, s) CaC₂O₄(s) + H₂O(gas, g)

CaC₂O₄(s)CaCO₃(s) + CO(g)

CaCO₃(s)CaO(s) + CO₂(g)

In a thermogravimetric analysis (TGA), the mass of a sample is monitored as the sample's temperature is steadily increased. A nonreactive gas is streamed over the sample to carry away any gaseous products. The figure shows the results of a TGA of a 100 g sample of CaC₂O₄·H₂O.