Question

5 gram of zinc carbonate is heated to a constant mass what weight of zinc oxide is formed and what volume of carbon dioxide gas is liberated at the same time

Answer 1

ZnCO3 → ZnO + CO2

It is a THERMAL DECOMPOSITION REACTION.

The first thing to do here is to calculate the relative formula mass of ZnCO3 and CO2.

RFM of ZnCO3 = 4 g + 1.2 g + (1.6 g x 3) = 10 g

RFM of CO2 = 1.2 g + (1.6 g x 2) = 4.4 g

The decomposition equation shows 1 ZnCO3 goes to 1 ZnaO and 1 CO2.

We have 5 g of ZNCO3, effectively we have half a ZnCO3.

5 g / 10 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 ZnCO3 to CO2:

4.4 g x 0.5 = 2.2 g

2.2 g of CO2 are obtained from decomposition of 5 g of ZnCO3.