posted by Anan on .
Equation: Fe2O3 + 2Al ---> 2Fe + Al2O3.
How many grams of Fe2O3 react with excess Al to make 475g Fe?
Can you show me step by step how to do it? My book says the answer is 679g Fe2O3.
The book is right.
ALL of these problems can be worked this way.
1. Write and balance the equation.
2. Convert what you have (in this case Fe) to moles. moles = grams/molar mass= ??.
3. Using the coefficients in the balanced equation, convert moles of what you have into moles of what you want (in this case Fe2O3).
moles Fe2O3 = moles Fe x (1 mole Fe2O3/2 moles Fe) = moles Fe x 1/2 = ??
4. Convert moles of what you have to the units you want (in this case grams). grams = moles x molar mass.
I get 679.0756 g which rounds to 679 to three significant figures (the number 675 limits you to 3 s.f.).