Molar Conversions & Molecular Formula Notes
Name: ____________________________________ Per: ______
I.
Two Step Conversions (1 Wheel)
a. A quantity of a substance can only be related to another quantity of the same
substance through the mole.
II.
Two Wheel Conversions
a. Composition stoichiometry is the branch of chemistry that deals with the
quantitative relationships between _____________________________________________________.
b. A quantity of a substance or species can only be related to a quantity of
another substance or species through the mole.

Example: How many carbon atoms are in 5.0 g of C3H8?
III.
Molar Volume
a. The molar volume of a substance is the space occupied by ____________________________________.
b. A substance’s molar volume is determined by the size and spacing of its particles although the size of the
particles has little effect on a gas’ molar volume because gas particles are so spread out.
c. Substances expand when heated and thus their molar volume is
greater at higher temperatures.
d. ________________________________________ states that equal
volumes of different gases, measured at the same temperature
and pressure, have equal numbers of particles.
e. For example, the molar volume of any gas at 0oC (or 273 K) and
101.3 kPa (or 1 atm) is approximately 22.4 L. This is known as
Standard Temperature and Pressure (STP)
IV.
You Try: How many liters of C3H8 (butane) contain 2.0 grams of
Carbon?
V.
Molar Volume and Density
a. Density is the amount of _____________ in a given ____________.
b. Density is a conversion factor that relates a substance’s mass
directly to its volume.
c. Example: The density of oxygen is 1.43 g/L, what is the molar volume of oxygen gas?
I.
Percent Composition
 Percent Analysis of H2O
What is the percent of Hydrogen in H2O?
II.
What is the percent of Oxygen in H2O?
Empirical Formula
a. The empirical formula is the
_________________________________ ratio of
atoms in a compound.
Percent composition in
chemistry deals with
masses so when
calculating it, one must
consider the grams that
each atom contributes to
the molecule or
compound.)
b. The molecular formula is the: ACTUAL
FORMULA of a compound giving the numbers
of each type of atom
III.
Steps to Finding Empirical Formula
a. Determine the grams of each element are present (if not given numbers, use % composition
data)
 Change % of mass to grams (assume you have 100 g)
 Example: 55%  55g
b. Convert grams to MOLES (divide by atomic mass) (empirical formula is comparison of moles)
c. Divide each answer by the smallest number of moles
d. Round your ratio to the nearest WHOLE number.
 You can round 1.97 to 2, but you can’t round 1.333 to 1.
 If there is a decimal like 1.33 – multiply ALL the subscripts by 3. How about 2.5? Multiply all the
subscripts by 2. Need to be able to recognize common ratios. If needed, multiply all the
subscript numbers by the smallest whole number that will get them to be whole numbers
Your set of whole numbers represent the subscripts for each atom in the empirical formula.
Helpful Rhyme: % to mass, mass to mole, divide by small, times ’til whole.
IV.
Example of Finding Empirical Formula
An unknown compound is composed of 81.8% carbon and 18.2% hydrogen. Determine the
empirical formula for the compound.
Percent to mass
Mass to mole
Divide by small
Multiply 'til whole
Practice Finding Empirical Formula
An unknown compound is composed of 39.99% C, 6.71% H and 53.29% O. Determine the empirical formula.
V.
Molecular Formula
a. Can be the same as empirical formula or a whole number ratio of it.
b. Examples:
 H2O is the empirical & molecular formula for water.
 CH2O is the _________________ formula for glucose,
ethanoic acid, and methanol.
The molecular formula for glucose is C6H12O6,
(six times the empirical ratio!)
VI.
Steps for Finding Molecular Formula
a. Find the empirical formula
b. Calculate the empirical formula mass
c. Divide the molecular mass (given in problem) of the compound by the empirical formula mass
d. Multiply each of the empirical formula subscripts by the whole number ratio (found in c)
VII.
Example of Finding Molecular Formula
A compound has an empirical formula of CH2 and a molecular mass of 42 g. Determine its
molecular formula.
Practice Finding Molecular Formula
A compound has an empirical formula of CH2 and a molecular mass of 56g. Determine its molecular formula.
Additional info: Sometimes a chemical reaction gives a product that has never been obtained before. In such a case, a
chemist determines what compound has been formed by determining which elements are present and how much of
each is there. This data can be used to obtain the formula of the compound. Previously, we used the formula of a
compound to determine the mass of each element present in a mole of the compound. To obtain the formula of an
unsworn compound, we do the opposite. That is, we use the measured masses of the elements present to determine
the formula.
-Empirical formula can be found from the percent composition of the compound.
-Molecular formula is the exact formula of the molecules present in a substance.
Molar Concentration
I.
Molarity – A useful unit of concentration
a. ___________________________ is any expression of the proportion of a chemical in a solution.
b. Molarity (M) is the number of _______________ of the chemical per liter of solution,
i. Ex: 1.8 M HCl means 1.8 mol HCl per litre of solution.
c. The molar concentration of a chemical is indicated by putting ________________________________
around the chemical’s formula
i. Ex: [HCl].
II.
Preparing a standard solution
a. A standard solution is a solution of ______________________________________________.
b. Example of preparing a standard solution: Explain how you would make 0.25 L of a 1.5 M sodium
chloride solution
III.
Ions in solution
a. The dissociation equation provides the ___________ of the ____________________ ions to each other
and to their ________________ compound.
b. CaCl2(s) 
c. Example: How many chloride ions are in 0.125 L of a 1.5 M CaCl2 solution