Question

Question #7b0d0

Answer 1

70 (1 s.f.) *fixed s.f.

Explanation:

Write the formula for iron(III) oxide: `Fe_2` `O_3`

Using their atomic masses, calculate the % of Fe in `Fe_2` `O_3`
m(Fe) = 55.85 AMU
m(O) = 16.00 AMU
In the compound, there are 2 moles of Fe and 3 moles of O. We have the atomic masses of 1 mole of each element, as written above.

1. Calculate the atomic mass of the compound
   2(55.85) + 3(16.00) = 159.7 AMU
2. Calculate the mass of Fe in the compound
   2(55.85) = 111.7
3. Divide the mass of Fe by the total mass of the compound, then multiply by 100 to get the % Fe in the compound
   (`111.7/159.7`) x 100 = 69.9436%

Now that you have the percentage of Fe in the compound, use it to calculate how much of the 100g sample would be Fe

`69.94/100` x 100g = 70 (1 s.f.)