stoichiometry help

Question

1.) how many grams of Fe₂O₃ can form from 29.2 grams of O₂?

2.) show the strategies for solving this problem (the question gives: Grams O_{2———>_______———>_______———> grams} Fe₂O₃)

3.) show the conversions required to solve this problem and calculate the grams of Fe₂O₃ (this question gives 29.2 g O₂ x ____ x_____ x ____ =g Fe₂O₃)

Answer 1

1.) how many grams of Fe₂O₃ can form from 29.2 grams of O2?

In order to obtain Fe₂O₃ from O₂, you obviously will also need some iron (Fe). So, we need to write a correctly balanced equation using Fe and O₂ to make Fe₂O₃:

4Fe + 3O₂ ==> 2Fe₂O₃ .. balanced equation

Next, we will convert 29.2 g O₂ to moles of O₂ using the molar mass of O₂ (32.00 g/mol)

29.2 g O₂ x 1 mole O₂ / 32.00 g = 0.9125 moles O₂

Next, we will use the stoichiometry of the balanced equation to determine moles and then grams of Fe₂O₃:

0.9125 mols O₂ x 2 mols Fe₂O₃ / 3 mols O₂ = 0.6083 mols Fe₂O₃ (molar mass 159.7 g/mol)

0.6083 mols Fe₂O₃ x 159.7 g / mol = 97.2 g Fe₂O₃ (to 3 significant figures)

Parts 2 and 3 are just a repeat of the procedure outlined above.

2.) grams O₂ --> moles O₂ --> moles Fe₂O₃ --> grams Fe₂O₃

3.) 29.2 g O₂ x 1 mol O₂/32.0 g x 2 mols Fe₂O₃ / 3 mols O₂ x 159.7 g Fe₂O3 / mol = 97.2 g Fe₂O₃

Answer 2

The first thing you're going to want to do is create a balanced equation.

In this case, the problem tells you O₂ is you reactant and Fe₂O₃ is your product. You need one more product (that iron needs to come from somewhere!), and its going to be iron metal.

So your unbalanced equation is Fe + O₂ ---> Fe₂O₃

I'll let you practice balancing that. Once you do, you want to follow a 3 step process to convert mass of one compound (oxygen) to mass of another (Fe₂O₃)

1. Convert the mass of oxygen to the number of moles of oxygen using the molecular weight of O₂ (get this from the periodic table).
2. Convert the moles of oxygen to the moles of Fe₂O₃ using the coefficients in your balanced reaction.
3. Convert the moles of Fe₂O₃ to the mass of Fe₂O₃ using the molecular weight of Fe₂O₃ (Use your periodic table to get the molecular weight)