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?

Convert 12.63 g Fe2O3 to grams Fe.

12.63 x (2*atomic mass Fe/molar mass Fe2O3) = ?
%Fe = (mass Fe/mass sample)*100 = ?

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.

To find the percent of iron in the sample of ore, you need to calculate the mass of iron and then divide it by the total mass of the sample, then multiply the result by 100.

For the first question:
1. Start by determining the mass of iron in the sample: Since all the iron in the sample is converted to Fe2O3 and the mass of Fe2O3 is given as 12.3 grams, you can assume that the molar mass of Fe2O3 is the sum of the atomic masses of iron and oxygen. The atomic mass of iron (Fe) is approximately 55.85 grams/mol, and oxygen (O) has an atomic mass of approximately 16.00 grams/mol. So the molar mass of Fe2O3 is 55.85 + (16.00 x 3) = 159.85 grams/mol.
To calculate the mass of iron, you need to convert the given mass of Fe2O3 to moles, using its molar mass. You can find the number of moles by dividing the mass of Fe2O3 by its molar mass: 12.3 grams / 159.85 grams/mol = 0.0768 moles.
Since Fe2O3 contains two moles of iron (Fe) per mole of Fe2O3, you can multiply the number of moles of Fe2O3 by 2 to get the number of moles of iron: 0.0768 moles x 2 = 0.1536 moles.
Finally, multiply the moles of iron by the molar mass of iron (55.85 grams/mol) to get the mass of iron: 0.1536 moles x 55.85 grams/mol = 8.58624 grams.

2. Now, calculate the percent iron in the sample by dividing the mass of iron by the original sample mass and multiplying by 100: (8.58624 grams / 33.2 grams) x 100 = 25.9%. Therefore, the percent iron in the sample of ore is 25.9%.

For the second question:

1. First, subtract the mass of the solid residue from the initial mass of the sample to find the mass of the magnesium carbonate that decomposed: 28.4288 grams - 16.0467 grams = 12.3821 grams.

2. The mass of the magnesium carbonate in the original sample is equal to the mass of the magnesium carbonate that decomposed: 12.3821 grams.

Therefore, the amount of magnesium carbonate present in the original sample is 12.3821 grams.

For the third question:

1. Follow the same steps as in the first question to find the mass of iron in the sample. Convert the mass of Fe2O3 (18.5 grams) to moles, then multiply by 2 to get the moles of iron, and finally multiply by the molar mass of iron (55.85 grams/mol) to get the mass of iron: (18.5 grams / 159.85 grams/mol) x 2 x 55.85 grams/mol = 6.45 grams.

So, the mass of iron in the sample of ore is 6.45 grams.