Molarity

1
Mole Applications

• Molarity
• Percent Composition
• Empirical Formula
• Molecular Formula

2
Molarity

• moles of solute (mol)
• volume of solution (L)
• Find the molarity of 2.34 moles of CoSO4 in 13.20
  L of solution

3
Example

• What mass of KCl is required to make 5.00 L of
  2.00 M KCl?

• Solution
• Multiply 5.00 L x 2.00 mol/L 10.0 moles KCl
  are required.
• Multiply 10.0 moles x 74.551 grams/mol.
• 746 KCl are required. (3 SF)

4
Percent Composition
Tells the relative mass each element contributes
to the mass of the whole compound.

• Formula
• Mass of one element X 100
• Mass of compound

5
Percent Composition
The formula for glucose is C6H12O6. What is the
percent composition of each element? (3 SF)
Answer 40.0 C 6.73 H 53.3 O
6
Find the percent composition of aluminum sulfate.

• Answer
• Al 15.8
• S 28.2
• O 56.1

7
Empirical Formula

• Simplest formula for the compound
• Smallest ratio of atoms

8
Identify the empirical formula(s).
C3H10 Na2S2O8 Hg2(NO3)2 MgC2O4
9

• A compound is analyzed to be
• 24.27 Carbon
• 4.07 Hydrogen
• 71.65 Chlorine
• Determine the empirical formula for the compound.

CH2Cl
10

• In 100.0-g of compound there are 43.64 g of
  phosphorus and
• 56.36 g of oxygen.
• Determine the empirical formula of the compound

P2O5
11
Molecular Formula

• Exact formula for compound
• Must know molar mass to find molecular formula

12
Example
The empirical formula of a compound CH2. Its
molar mass is 42 g/mole. Which of these could be
the molecular formula? C2H4 C3H6 C4H8 C5H10

13
Molecular formulas

• We determine an empirical formula to be CH5N, but
  we know the molar mass is not 31.06 g/mol but is
  really 93.18 g/mol. Determine the molecular
  formula for the compound.

C3H15N3
14

• Caffeine contains
• 49.48 carbon
• 5.15 hydrogen
• 28.87 nitrogen
• 16.47 oxygen by mass
• The molar mass is 194.2 g/mol
• Determine the molecular formula

C8H10N4O2