AP Chemistry
Podcast 1.2
Calculating Percent Yield, Percent
Composition, Percent Error,
Empirical and Molecular Formulas
Percent Yield
Rules
1. Balanced Equation
2. Write amount given under the reactant that has
a value
3. You will be given an amount of product (write
this under the product) this is the actual amount
produced.
4. Convert given reactant amount to same product
that was given.
5. Percent Yield =
Example: Percent Yield
Nitrogen gas reacts with hydrogen gas to make
ammonia (NH3 ). 15.5 L of N2 reacts at STP to make
30 L of ammonia. What is the percentage yield?
Percent Composition
• Find the percentage composition of a
chemical by finding the total molar mass of
the compound…find the mass percent of each
element in the compound.
• Example: NH4NO3
Percent Error
Empirical Formula:
Rules
1. Percent to mass
2. Mass to moles
3. Divide by small
4. Times to whole
Example: Empirical Formula
Determine the empirical formula of a compound
with 52.8% Sn, 12.4% Fe, 16% C, and 18.8% N.
Molecular Formulas
1. Molecular formulas are the actual number of
atom’s in a molecule…not just the simplest
whole number ratio.
2. The molar mass of the empirical formula is
always a multiple of the molecular weight.
3. Use the molecular weight to determine what
factor you need to multiple the empirical
formula to find the molar formula.
Example: Molecular Formula
Determine the molecular formula for a compound that
contains 22.5% Na, 30.4% P and 47.1%O and a molar
mass of 306 g/mol.