The Mole

• The Avogadro constant = 6.02 x 10^23
• One mole of any substance is just an amount of the substance that contains an Avogadro number of particles (6.02 x 10^23)
• The mass of the number of atoms or molecules of any substance is exactly the same number of grams as the Ar or Mr of the element or compound (6.02 x 10^23)
• 1 mole of atoms or molecules of any substance will have a mass in grams equal to the Ar of Mr for that substance
• Carbon has an Ar of 12
• Nitrogen gas, N2 has an Mr of 28
• Carbon dioxide, CO2 has an Mr of 44
• 1 mole of carbon weighs 12 g
• 1 mole of N2 weighs 28 g
• 1 mole of CO2 weighs 44 g
• [Mass in g (of an element or compound)] / [Mr (of the element or compound)] = number of moles
• 'mol' is the symbol for the unit mole
• Example

  How many moles are there in 66 g of CO2?

  1)Calculate the Mr of CO2

  > Mr of CO2 = 12 + (16 x 2 ) = 44

  2) Use the formula to find out how many moles there are

  > No. of moles = mass (g) / Mr = 66 / 44 = 1.5 mol
• You can rearrange the equation using a fomula triangle

  
• Example

  What mass of carbon is there in 4 moles of carbon dioxide?

  >There are 4 moles of carbon in 4 moles of CO2

  1)Do the equation 'no. of moles x Mr'

  > So the mass of 4 moles of carbon = 4 x 12 = 48 g