Download Steps in Solving Molar Mass Problems:

General Steps to Follow in Solving Molar Mass, GMA, Percent Composition,
Empirical & Molecular Formula Problems
Steps in Solving Molar Mass Problems:
1. If the chemical formula is not given to you, determine the correct chemical formula of the compound.
2. Use the subscripts in the chemical formula to determine how many moles of each given element are present in
one mole of the compound.
3. Add up the masses of each of the elements present in the compound to determine the Molar Mass of the
compound.
÷
G
molar
mass
X
X
M
6.02x1023
A
÷
Steps in Solving GMA (grams↔moles↔atoms) Problems:
1. Determine the Molar Mass of the compound using the process above.
2. Follow the GMA map performing each calculation using either the molar mass or Avogadro’s number (6.02x1023).
Steps in Solving Percent Composition Problems:
1. If you aren’t given the name or chemical formula of the compound:
a. Calculate the total mass of the sample or compound.
b. Divide the mass of the desired element by the total mass of the sample or compound.
2. If you are given the name or chemical formula:
a. Determine the Molar Mass of the compound using the process above.
b. Divide the mass of the desired element by the Molar Mass of the compound.
Steps in Solving Empirical (Simplest) Formula Problems:
Empirical Formula – the smallest whole-number ratio of all the elements in a compound.
1. If you are given the Percent Composition of each element in the compound:
a. Convert the % of each element into in mass by assuming you have 100 grams of the compound.
b. Use the GMA map to convert the mass of each element into the number of moles of each element.
c. “Divide all moles by small moles!”
d. Your answers to Part c) should all be whole numbers or convenient fractions of whole numbers
i. e.g. – 1.25, 1.33, 1.50, 1.66, 1.75
e. Place the number from Part c) as a subscript next to its respective element.
i. If all the subscripts are whole numbers, you are done – THIS IS THE EMPIRICAL FORMULA
ii. If any of the subscripts are fractions (decimals) as in Part d i), you must double, triple, or
quadruple the ENTIRE formula you’ve written in order that all the subscripts are WHOLE
NUMBERS.
iii. Example: (C1H1.33O1) x 3 = C3H4O3 – THIS IS THE EMPIRICAL FORMULA
2. If you are given the mass (grams) of each element present in the compound, simply skip Step 1a) above, and
start from Step 1b).
Steps in Solving Molecular (True) Formula Problems:
Molecular Formula – the actual number of each element in a compound.
1. Calculate the Empirical Formula of the Compound.
2. Calculate the Molar Mass of the Empirical Formula
3. Divide the given Molar Mass (or Molecular Weight) of the actual compound by the Molar Mass of the Empirical
Formula
a. This will yield a small whole number.
4. Multiply the entire Empirical Formula by the small whole number from 3a).
b. This is the Molecular Formula of the compound.