High School
SAT
ACT
University
MCAT
LSAT
DAT
Wize High School Grade 11 Chemistry Textbook > Quantities in Chemistry

The Mole and Molar Mass

Naming ConventionsPrevious Section
Empirical FormulasNext Section
Popular Courses
Find My Course
0:00 / 0:00

Moles and Molar Mass

  • A mole is the exact number of atoms in 12g of carbon
  • If we know that: 1 dozen = 12\boxed {\text {1 dozen = 12}}, then1 mole=6.022×1023\boxed{\text {1 mole} = 6.022 × 10^{23}}
  • The above value, 6.02x1023 is referred to as Avogadro's number (NA)
NA=6.022×1023 mol−1\boxed {N_A = 6.022 × 10^{23}\ \text{mol}^{-1}}
PAGE BREAK

Molar Mass

  • Molar mass is the mass of one mole of particles of that substance
  • Units for molar mass are g/mol.
  • Molar mass is abbreviated using the symbol M Example: Molar mass of elemental oxygen can be represented as MO2M_{O_2}

Molar Mass of Elements

  • Found in periodic table. Example: Molar mass of sodium
  • When looking at molar mass of molecular elements, you have to multiply the molar mass of the element by the number of atoms per molecule Example:Molar mass of elemental chlorine

Molar Mass of Ionic and Molecular Compounds

  • The molar mass of a compound is equal to the sum of the molar mass of each entity in the compound. Example: Molar mass of sulfuric acid, H2SO4
PAGE BREAK


0:00 / 0:00

Example: Using Avogadro's Number

Calculate the number of Cu atoms if you have 0.635g of Cu.


1) Find number of moles given that mass
n=mMn=\frac{m}{M} = Mass of Cu/Atomic mass = 0.635/63.5 =0.01 mole

2) Now we can find the # of Cu atoms (here N will = # of atoms)
n=NNAn=\frac{N}{NA} N= No. of moles × Avogadro constant = 0.01 × 6.02× 1023 = 6.02 × 1021 Cu atoms.

Practice: Calculating Molar Mass

Calculate the molar mass of H2O. Give your answer rounded to the nearest whole integer; do not include units.

Practice: Using Avogadro's Number and Molar Mass

If we are told that a sample of CO2(s) weighs 11g, how many moles of CO2 are present in the sample?

Practice: Converting Mass to Number of Atoms

Calculate the number of nitrogen atoms in 2.25 g of Bi(NO3)3.