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Aim: How to convert from moles to volume and vice versa Avogardo’s Hypothesis Avogadro's hypothesis says that the same volume of gas contains the same number of particles. It does not matter what gas you have, they all contain the same number of particles provided that they are at the same temperature and pressure. STP Volume of gas and temperature are usually measured at STP. Standard temperature and pressure (STP) means temperature of 0oC and a pressure of 101.3 kPa, or 1 atmosphere (atm). At STP, 1 mole or 6.02 x 1023 representative particles of any gas occupies a volume of 22.4 L. Calculating from moles of gas to volume of gas Conversion Factor Volume of gas = moles of gas x 22.4 1 Calculating the volume of a gas at STP Determine at STP. 1. Identify the volume, in liters, of 0.60 mol SO2 gas known and unknown. Known 1 mol = 22.4 L 0.60 mol SO2 Unknown volume of 0.60 mol SO2 2. Set up equation 22.4 Volume = 0.60 mol SO2 x SO2 1 Volume = 13 L SO2 What is the volume of these gases at STP? a. 3.20 x 10-3 mol CO2 3.20 x 10-3 mol CO2 x 22.4 L / 1 mol = 0.0717 L CO2 b. 3.70 mol N2 3.70 mol N2 x 22.4 L / 1 mol = 82.9 L N2 Converting from volume of gas to moles of gas Conversion Factor 1 Moles of gas = volume of gas x 22.4 Calculating number of moles of a gas at STP How many moles of helium at STP will fit into a 39.6 L container? 1. Identify known and unknown. Known Unknown 1 mol = 22.4 L # of moles 39.6 L 2. Set up equation 1 Moles = 39.6 L He x 22.4 Moles = 1.77 mol He How many moles of argon atoms are present in 11.2 L of argon gas at STP? 11.2 x 1mol / 22.4 L = 0.500 moles Calculating Molar Mass From Density Reminder: Density= mass / volume Density = molar mass / molar volume Molar mass = density x molar volume 22.4 = x 1 Molar Mass density Molar volume Calculating molar mass of gas at STP The desnity of a gaseous compound containing carbon ad oxygen is found to be 1.964 g/L at STP. What is the molar mass of this compound. 1. List known and unknown. Known Density = 1.964 g/L 1 mol = 22.4 L Unkown molar mass ? 2 . Set up equation. 1.964 Molar mass = 1 x 22.4 1 Molar mass = 44.0 g/mol What is the density of krypton gas at STP 1. Find molar mass of krypton molar mass = 83.8 g/mol 2. Set up Equation Density (g/L) = molar mass/ molar volume 83.8 / Density= or Density= (83.8 g/1 mol) x (1 mol / 22.4 L) 22.4 / Density of Kr = 3.74 g/L