The mole has three values that can be used to do calculations with the mole. They are:
  • a mass = the gram molecular weight or molar mass
  • a volume of one mole in the gas state at 0 C and 100 kPa.(called standard temperature and pressure STP ) = 24.5 L.
  • a # of particles = 6.023* 10 23
This means that 9 separate calculations can be done with the mole. These can be summarized into one device , that can help students understand how to do the calculations. This device is often termed the mole triangle and is shown below.
  • To use the device students need only identify what information they are starting with and what they are asked to calculate. Students then follow the arrows and perform the operations indicated.
Examples and Assignments
Examples
1. Calculate the mass in grams of 35 moles of CaCO3.
  • Given information is 35 moles of CaCO3.
  • Asked to calculate the mass in grams.
  • The mole triangle indicates that you should multiply the 35 moles by the molar mass of CaCO3.

Step 1; Calculation of molar mass
1 * 40.08 g = 40.08 g
1 * 12.01 g = 12.01 g
3 * 16.00 g = 48.00 g
1 mole = 100.09 g
Step 2; Calculation of Answer
35 moles * 100.09 g/mol = 3503.15 g
3500 g rounded to 2 significant figures
 
2. Calculate the # of molecules in 820 L of SO2 (g) given off by a chemical plant at STP.
  • The given information is 820 L of SO2 (g)at STP.
  • Information you are asked to find is the # of particles.
  • The mole triangle indicates that you should divide 820 L by the molar volume to calculate moles and then multiply the moles by 6.023 * 10 23 p/mol.
Step 1;Calculation of moles
820 L / 25.4 L/mol. = 32.28 mol.
Step 2; Calculation of Answer
32.28 mol. * 6.023 *10 23 p/mol. = 1.9 *10 24 particles

Assignment # 2: Mole Calculations using a periodic table
  1. Calculate the mass of 65 L of carbon dioxide ( CO2 ).
  2. Calculate the volume of 78 g of tetraphosphorus hexaoxide ( P4O6 ).
  3. Calculate the volume of 47 moles of nitrogen dioxide ( NO2 ) gas at STP.
  4. Calculate the number of particles in 120 grams of sodium nitrate.
  5. Calculate the # of molecules in 89 L of CO gas at STP.
  6. Calculate the mass of 1.35 * 10 24 molecules of sulfur trioxide gas at STP.
  7. Calculate the volume of 63 moles of dinitrogen tetraoxide.
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