CHEM 205 lecture 4

• Mole


  6.022x10^23 (Avogadro's number) atoms
• Molar Mass (MM or M)


  Mass in grams of one mole of substance
• Ionic compounds


  MM = formula weight
• Molecular compounds


  MM = molecular weight
• Combustion analyzer


  1. Sample is weighed and then burned in a furnace by adding way too much oxygen

  2. All carbon converts to carbon dioxide

  3. All hydrogen is converted to water
• Compound formulas % composition

  Mass % = (mass element A in sample)/(mass total of sample) x 100
• Empirical formula steps


  1. Mass % divided by 100, multiplied by 100 grams = mass of element in 100g sample

  2. Find the molar mass (mass of element multiplied by number of atoms of that element)

  3. Divide mass by MM to get amount of moles of an element

  4. Mole ratio: take number of moles of an element and divide it by the least abundant (element with smallest number of moles) *molecular formula*

  5. Divide formula weight/ molecular weight by MM to see if mole ratio needs to be scaled up or not
• Hydrated compounds


  Dry but contain molecules of water