Stoichiometry Review Sheet

And Practice Problems

 

A. Skill 1: Conversions between Mass, Moles, and # of Molecules

 

                  # Molecules                                       Moles                                      Mass (grams)

                                                      AvogadroÕs                        Molar Mass

                                                      Number                                    (g/ mole)

 

1) Convert from mass ˆ moles.

Example: Convert 12.6 g of Al(NO3)3 to moles.

 

 

 

 

2) Convert moles ˆ mass.

Example: How many grams of Na2SO4 are there in 0.66 moles of Na2SO4?

 

 

 

 

3) Convert # of molecules ˆ moles

Example: How many moles are in 3.00 x 1024 molecules of Pt?

 

 

 

 

 

4) Convert moles ˆ # of molecules

Example: If you have 3.16 moles of Au, how many molecules of Au do you have?

 

 

 

 

 

5) Convert mass ˆ # molecules.

Examples: If you have 120.5 g of Ni, how many Ni molecules do you have?

 

 

 

 

 

6) Convert # molecules ˆ mass

Example: You have 8.7 x 10 23 molecules of Fe.  What mass of Fe do you have?

 

 

B. In reaction equations, relate reactants (mass or moles) to products (mass or moles).

 

                  Mass of                                Moles of                               Moles of                               Mass of

Reactants (g)                 Reactants                           Product                                 Products (g)

 

 

 

                                    Molar Mass                       Mole Bridge (ratio)                       Molar Mass

                          (Periodic Table)                (from balanced rxn eqn)                    (Periodic Table)

 

1) Convert moles of reactants to moles of products.

Example: Given the equation  P2O5  +  3 H2O ˆ  2 H3PO4

If you have 9 moles of H2O how many moles of H3PO4 can you make?

 

 

 

 

 

 

 

2) Convert mass of reactants to mass of products.

Example: If you have 25.0 g of P2O5  , how many grams of H3PO4 can you produce?

 

 

 

 

 

3) Compare moles of one reactant needed to react with moles of another reactant.

Example: How many moles of P2O5 are needed to react completely with 7.66 moles of water?

 

 

 

 

 

4) Compare mass of one reactant needed to react with mass of another reactant.

Example: How many grams of water are needed to react completely with 17.64 g of P2O5 ?

 

 

 

 

 

5) Calculate how many grams of one reactant are needed to produce a given mass of a product.

Example: How many grams of H2O are needed to produce 16.0 g of H3PO4?

 

 

 

 

 

6) Given amounts of 2 or more reactants, determine which is the limiting reagent.

Example: You have 25.0 g each of P2O5 and H2O.  Which is the limiting reagent?

 

 

 

 

 

 

 

 

 

7) Calculate theoretical yield.

Example:  If you start with 37.64 g of P2O5, what is the theoretical yield of H3PO4?

 

 

 

 

 

8) Calculate % yield.

Example: You run the reaction listed above and obtain 0.379 g of H3PO4.  What was your percent yield?