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
- Given mass to moles:
- Divide the given mass by the molar mass.
- Moles to mass:
- Multiply the number of moles by the molar mass.
- Moles to particles:
- Multiply the number of moles by Avogadro's number.
- Particles to moles:
- Divide the number of particles by Avogadro's number.
- Moles of a gas to volume at STP:
- Multiply the number of moles by 22.4 liters.
- 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
- Calculate the number of moles in 25 grams of sodium chloride (NaCl).
- How many atoms are present in 0.5 moles of carbon?
- What is the volume of 3 moles of oxygen gas at STP?