Question

I have 3 I don't understand how to do.

A 33.2 g of iron ore is treated as follows. The
iron in the sample is all converted by a series
of chemical reactions to Fe2O3. The mass of
Fe2O3 is measured to be 12.3 grams. What
was the percent iron in the sample of ore?
Answer in units of %


A 28.4288 g sample of impure magnesium car-
bonate was heated to complete decomposition
according to the equation
MgCO3(s) ! MgO(s) + CO2(g) .
After the reaction was complete, the solid
residue (consisting of MgO and the original
impurities) had a mass of 16.0467 g. Assum-
ing that only the magnesium carbonate had
decomposed, how much magnesium carbon-
ate was present in the original sample?
Answer in units of g

A 5.7 g sample of iron ore is treated as follows.
The iron in the sample is all converted by a
series of chemical reactions to Fe2O3. The
mass of Fe2O3 is measured to be 18.5 g. What
was the mass of iron in the sample of ore?

Answer 1

Convert 12.63 g Fe2O3 to grams Fe.
12.63 x (2*atomic mass Fe/molar mass Fe2O3) = ?
%Fe = (mass Fe/mass sample)*100 = ?

Answer 2

I worked #2 for you above. See that response.

#3.
Isn't this just like #1 except you don't do percent? Convert 18.5 g Fe2O3 to grams Fe in the sample.