Suppose that 5.82 g of solid Fe2O3 is added to 24.3 mL of 0.577 M HCl solution. What is the concentration of the Fe3+ that needed to react with all the HCl? What mass of Fe2O3 will not have reacted?

Question

Please help im having trouble getting it right.

Answer 1

You'll need the stoichiometry from the reaction:

Fe₂O₃ + 6HCl ⇒ 2FeCl₃ + 3H₂O

The question is odd in that it asks for concentration needed to react when the reactant is solid and only the excess reactant will be Fe³⁺ in solution. We can still grind it out and assume that the HCl is limiting and that the unreacted Fe₂O₃ does not dissolve. (it need acidity to do so)

Let's just calculate how much Ferric Oxide (FO) that is reacted:

24.3 ml HCl (1 liter/1000 ml)(.577 moles HCl/liter)(1 mole FO/6 moles HCl)(159.69 g/mole FO) = g FO

Grams unreacted = 5.82 - g FO reacted

Take moles of FO reacted (you can work this out by stopping before the final multiplication above)

and multiply by 2 moles Fe²⁺/ mole FO

You need to divide this by the liters of solution which you can only take to be .0243 liters.