1. Moles

2. The Mole
1 dozen = 12
1 mole = 6.02 x 1023
The mass of 1 mole of an element is the mass on the periodic table
1 mole of Hydrogen = 1 g of Hydrogen
1 mole of Helium = 4 g of Helium

4. Molar Mass Molar mass is the mass of 1 mole of a substance
Units: g/mol
The molar mass of an element is the mass number for the element that we find on the periodic table
The molar mass of a compound is the mass of the elements in that compound added together. We have special terms for the molar mass of a compound.

5. } } Molar Mass Calculate the molar mass of NaCl: Na: 1 x 23 = 23
Cl: 1 x 35 = 35
Calculate the molar mass of Na(NO3)2:
N: 2 x 14 = 28
O: 6 x 16 = 96 }
= 58 g/mol }
= 147 g/mol

6. Conversion Review What is a ratio?
A comparison of two things which are equal to one another
Remember how we use ratios to perform metric conversions:
How many centimeters in 5 meters?
5 m x 100 cm = 500 cm
1 m

7. Conversions We use molar mass as a ratio for conversions
Molar mass = g/mol
We use Avogadro’s number as a ratio for conversions
6.02 x atoms, molecules / 1 mol

8. Conversions To convert from grams to moles:
12 g Helium x 1 mole Helium = 3 moles Helium
4 g Helium
To convert from moles to atoms:
3 moles He x x 1023 atoms He = 1.81 x 1023 atoms He
1 mole He

9. Conversion Review
Remember when converting between two units with prefixes we used two ratios.
We always go through the base unit:
How many kilometers in 500 centimeters?
500 cm x 1 meter x 1 kilometer = km
100 cm m

10. Conversions To convert from grams to atoms we use two ratios
Just like we go through the base unit for two- step metric conversions, we go through the mole for two-step mole conversions

11. conversions To convert from grams to atoms:
16 g He x 1 mole He x x 1023 atoms He = 2.41 x 1023
4 g He mole He atoms He
To convert from atoms to grams:
3.5 x x mole He x g He = 2.33 g
atoms He x 1023 atoms He mole He