Question

Dolomite is a mixed carbonate of calcium and magnesium that decomposes to CO2 and the metal oxides MgO and CaO upon heating. When 15.42 g of dolomite is heated, 7.85 g of MgO and CaO are produced. What is percent by mass of MgCO3 in the original sample of dolomite?

Answer 1

47%

Step-by-step explanation:

MgCO₃ (s) → MgO (s) + CO₂ (g)

CaCO₃ (s) → CaO (s) + CO₂ (g)

_______________________

MgCO₃ (s) + CaCO₃ (s) → MgO (s) + CaO (s) + 2CO₂ (g)

MgO: 40.3044 g/mol

MgCO₃: 84.3139 g/mol

CaO:56.0774 g/mol

CaCO₃: 100.0869 g/mol

CO₂: 44.01 g/mol

15.42 g is the total mass of dolomite.

7.85 g is the sum of MgO and CaO produced.

This means that 7.57 g of CO₂ were produced.

44.01 g CO₂_____ 1 mol

7.57 g CO₂ _____ x

x = 0.172 mol CO₂

Considering the global reaction, we had 0.172/2 = 0.086 mol of MgCO₃ in the original sample.

1 mol MgCO₃ _______ 84.3139 g

0.086 mol MgCO₃ ___ y

y = 7.25 g

15.42 g dolomite ______ 100%

7.25 g MgCO₃ ________ z

z = 47%