Question

For 15mg of unknown (assuming 50% caco3) calculate the mass change if heated to 840c?

Answer 1

CaCO3 decomposition:

CaCO3 -> CaO + CO2

The first thing to do here is to calculate the relative formula mass of CaCO3 and CO2.

RFM of CaCO3 = 40 g + 12 g + (16 g x 3) = 100 g

RFM of CO2 = 12 g + (16 g x 2) = 44 g

The decomposition equation shows 1 CaCO3 goes to 1 CaO and 1 CO2.

We have 50 g of CaCO3, effectively we have half a CaCO3.

50 g / 100 g = 0.5

In order to get the mass of CO2 we need to times the RFM of CO2 by 0.5 (or divide by 2) because of the ratio of CaCO3 to CO2:

44 g x 0.5 = 22 g

22 g of CO2 are obtained from decomposition of 50 g of CaCO3.