Mole Concept Quick Revision Sheets

Key Concepts

• Mole: A unit of measurement for the amount of a substance.
• Avogadro's Number: The number of atoms, molecules, or ions in one mole of a substance (approximately 6.022 x 10^23).
• Molar Mass: The mass of one mole of a substance, expressed in grams per mole (g/mol).
• Molar Volume: The volume occupied by one mole of a gas at standard temperature and pressure (STP), which is approximately 22.4 liters.

Formulas

• Number of moles (n) = Mass (m) / Molar mass (M)
• Number of particles (N) = Number of moles (n) x Avogadro's number (NA)
• Volume of a gas (V) = Number of moles (n) x Molar volume (Vm)

Calculations

1. Given mass to moles:
   • Divide the given mass by the molar mass.
2. Moles to mass:
   • Multiply the number of moles by the molar mass.
3. Moles to particles:
   • Multiply the number of moles by Avogadro's number.
4. Particles to moles:
   • Divide the number of particles by Avogadro's number.
5. Moles of a gas to volume at STP:
   • Multiply the number of moles by 22.4 liters.
6. Volume of a gas at STP to moles:
   • Divide the volume by 22.4 liters.

Examples

• Example 1: How many moles of water are present in 18 grams of water?
  • Molar mass of water = 18 g/mol
  • Number of moles = 18 g / 18 g/mol = 1 mole
• Example 2: How many molecules are present in 2 moles of hydrogen gas?
  • Number of molecules = 2 moles x 6.022 x 10^23 molecules/mol = 1.2044 x 10^24 molecules

Practice Problems

1. Calculate the number of moles in 25 grams of sodium chloride (NaCl).
2. How many atoms are present in 0.5 moles of carbon?
3. What is the volume of 3 moles of oxygen gas at STP?