Gravimetric stoichiometry is the branch of stoichiometry that deals with using the mass of one substance to calculate the mass of another substance in a chemical reaction.
For example, in the reaction
##”A → B”##
gravimetric stoichiometry asks the questions, “What mass of ##”B”## can be formed from ##x## g of ##”A”##?” and “What mass of ##”A”## is required to form ##x## g of ##”B”##?”
You always use the same type of steps.
- Write the balanced chemical equation.
- Convert ##”mass of A” → “moles of A” → “moles of B” → “mass of B”##.
EXAMPLE
Calculate the mass of iron(III) oxide that can be produced by the reaction of 500 g of iron with excess oxygen.
Solution
Step 1. Write the balanced chemical equation.
##”4Fe” + “3O”_2 → “2Fe”_2″O”_3##
Step 2. Do the conversions.
##500 color(red)(cancel(color(black)(“g Fe”))) × (1color(red)(cancel(color(black)(“mol Fe”))))/(55.84 color(red)(cancel(color(black)(“g Fe”)))) × (2 color(red)(cancel(color(black)(“mol Fe”_2″O”_3))))/(4 color(red)(cancel(color(black)(“mol Fe”)))) × (“159.7 g Fe”_2″O”_3)/(1 color(red)(cancel(color(black)(“mol Fe”_2″O”_3)))) = “715 g Fe”_2″O”_3##
