Homework Help: Chemistry

Posted by Chris on Monday, October 29, 2012 at 2:23am.

A sample weighing 3.064 g is a mixture of Fe2O3 (molar mass = 159.69) and Al2O3 (molar mass = 101.96).

When heat and a stream of H2 gas is applied to the sample, the Fe2O3 reacts to form metallic Fe and H2O(g). The Al2O3 does not react.

If the sample residue weighs 2.407 g, what is the mass fraction of Fe2O3 in the original sample?

I am not exactly sure where to start with this question. Would this be correct?

Mass of Fe2O3 = [(2.407 g - mass of Al2O3) / 55.85 g/mol] x (1 mol Fe2O3 / 2 mol Fe) x 159.69 g/mol

Chemistry - Steve, Monday, October 29, 2012 at 2:21pm
Actually, the mass of Fe in the residue is 2.407-Al2O3. The Fe2O3 has all lost its oxygen, leaving only Fe.

So, if you started out with x moles of Fe2O3 and y grams of Al2O3, then converting the Fe2O3 to grams,

159.69x + y = 3.064
55.85(2x) + y = 2.407

The equations may look a bit funny, but we really don't have to convert the moles of Al2O3 to grams, since the mass doesn't change. And, of course the (2x) appears because each mole of Fe2O3 has 2 Fe atoms in it.

Solving the equations yields

x = 0.01369 moles Fe2O3
y = 0.8778 grams of Al2O3

Now we need to convert the moles back to grams: .01369 moles = 2.1862 grams Fe2O3

2.1862/3.064 = 71.35%
Chemistry - PS - Steve, Monday, October 29, 2012 at 2:23pm
Actually, we really didn't have to convert the moles back to grams, since we had the mass of Al2O3 already. Just subtract its fraction from 100%.

Answer this Question

Related Questions

chemistry - The vapour denisty of a mixture containing NO2 & N2O4 is 38.3 at...
Chemistry - A 500g iron (Fe) rod was left in air for a long period of time, and ...
chemistry - how many atoms of iron are in .0750 moles of the compound Iron(III) ...
chemistry - a sample mixture of ch4 and c2h6 weighing 0.732 g burned to give 2....
Chemistry - Consider the equation: A + 4B=3C+3D, when equal masses of A and B ...
Chemistry - A .405 g sample of gas contains .0050 moles. What is the molar mass ...
Chemistry - In 2.00 min, 28.4 mL of He effused through a small hole. under the ...
chemistry - the major commercial aluminium ore is bauxite,AlO3.H2O(s).What is ...
chemistry - In the chemistry exp molar mass of a volatile liquid what will be ...
Chemistry - A rock sample contains only Sb2S3 and FeS. If 835g of the sample ...

For Further Reading

First Name:
School Subject:
Answer: