Chapter 8
Chemical Composition
- Atom have very tiny masses, so scientists made a unit to avoid using very small
numbers
- 1 atomic mass unit (amu) = 1.66 x 10-24 g
- The average atomic mass for an element is the weighted average of the masses of all
the isotopes of an element
o E.g. The mass of Carbon = 12.01 amu -> 12.01 x 1.66 x 10 -24 g = 1.99 x 10-23 g
Mole
- 1 mole of anything = 6.022 x 1023
units/atom of that thing (Avogadro’s
number)
Molar mass
Mass in grams of one mole of the substance:
- Molar mass of N = 14.01 g/mol
- Molar mass of N2 = 28.02 g/mol
Molar mass = mass (g) / mole (mol)
mass of the sample (g)
Moles of a compound = g
molar mass of thecompound ( )
mol
Mass of a sample = (moles of sample in grams) (molar
mass of compound)
Equations
÷ ×
Molecules 6.022 x 10 23 Moles Molar mass Grams (g)
× ÷
Chemical Composition
- Atom have very tiny masses, so scientists made a unit to avoid using very small
numbers
- 1 atomic mass unit (amu) = 1.66 x 10-24 g
- The average atomic mass for an element is the weighted average of the masses of all
the isotopes of an element
o E.g. The mass of Carbon = 12.01 amu -> 12.01 x 1.66 x 10 -24 g = 1.99 x 10-23 g
Mole
- 1 mole of anything = 6.022 x 1023
units/atom of that thing (Avogadro’s
number)
Molar mass
Mass in grams of one mole of the substance:
- Molar mass of N = 14.01 g/mol
- Molar mass of N2 = 28.02 g/mol
Molar mass = mass (g) / mole (mol)
mass of the sample (g)
Moles of a compound = g
molar mass of thecompound ( )
mol
Mass of a sample = (moles of sample in grams) (molar
mass of compound)
Equations
÷ ×
Molecules 6.022 x 10 23 Moles Molar mass Grams (g)
× ÷
