Flashback

1
Flashback
In your notes answer the following question to
the best of your ability 1.) How many atoms
would there be in one mole? 2.) What would be
the mass of one mole of Carbon atoms? 3.) What
would be the mass of 2 moles of H2O?
2
The MoleBy Ms. Buroker
3
What is the Mole?

• The mole is the SI base unit used to measure
  the amount of a substance.
• commonly abbreviated mol
• The mole can be defined as the number equal to
  the number of carbon atoms in 12.01 grams of
  carbon.

4
Avogadros Number

• One mole of something consists of 6.022 x 1023
  units of that substance.
• 1 mol 6.022 x 1023 particles

Molecules
Atoms
Formula Units (Ionic Compounds)
5

• 1 mole of any element has a mass in grams that
  is equal to its average atomic mass

Silver (Ag)
Lead (Pb)
Average atomic mass of this element 107.9 amu 207.2 amu
Mass of this sample 107.9 g 207.2 g
Number of atoms in this sample 6.022 x 1023 atoms 6.022 x 1023 atoms
6
Molar Mass

• The molar mass of an element is the mass in
  grams of one mole of any pure substance.
• The molar mass of a compound or molecule is
  equal to the sum of the mass (in grams) of the
  elements involved.

EXAMPLE CHCl3 C 12.01g/mol H 1.01g/mol Cl
35.45g/mol x 3 106.35g
7
Mole Relationship and Compounds

• A chemical formulas tell us the number of atoms
  that make the compound but, it can also tell us
  something about the number of moles of atoms in
  the compound!
• For example CaCl2

1 calcium atom In 1mol of CaCl2, there is 1mol of
calcium
2 chlorine atoms In 1mol of CaCl2, there are
2moles of chlorine
8
Lets Practice!!

• Determine the number of moles of chloride ions
  in 2.50mol ZnCl2
• 5.00mol Cl-
• Calculate the number of moles of each element in
  1.25mol glucose (C6H12O6)
• 7.50mol C
• 15.0mol H
• 7.5mol O

9
Some Vocabulary

• Percent Composition The percent by mass of each
  element in a compound.
• Empirical Formula The formula with the smallest
  whole number ratio of the elements.
• Molecular Formula The formula which specifies
  the actual number of atoms of each element in one
  molecule or formula unit.

10
Percent Composition
Percent by Mass

• Mass of element
• Mass of compound

X 100
Examples Sodium hydrogen carbonate, also called
baking soda, is an active ingredient in some
antacids used for the relief of indigestion.
Determine the percent composition of sodium
hydrogen carbonate.
11
EMPIRICAL FORMULAS

• Empirical formulas may or may not be the same as
  the molecular formula
• Example Hydrogen peroxide
• empirical formula HO
• molecular formula H2O2

12
How Do I Find the Empirical Formula?

• 1.)Find the number of moles of each element.
• If given percent composition- assume 100.0g
• 2.) Calculate the simplest ratio of moles of the
  elements by dividing each number of moles by the
  smallest whole number ratio.
• If the number are not whole, then multiply
  by the smallest number that will produce a ratio
  of whole numbers.

13
MOLECULAR FORMULAS

• Experimentally determined molar mass
• Mass of Empirical Formula

n

Multiply the numbers in the empirical formula by
the value of n
Molecular formula (empirical formula) n