VIEWS: 84 PAGES: 22 POSTED ON: 9/22/2012
Mole-Mass and Mole-Volume Relationships The Mole-Mass Relationship • To convert the mass of a substance to the number of moles of the substance you have to use the molar mass of an element or compound. • Mass = # of moles x (mass/1mole) The Mole-Mass Relationship • EX: the molar mass of NaCl is 58.5 g/mol, so the mass of 3.00 mol NaCl is calculated: o Mass of NaCl = 3 mol x (58.5 g/1 mol) o = 176 g • When you measure 176 g of NaCl on a balance, you are measuring 3.00 moles of NaCl. The Mole-Mass Relationship Practice • What is the mass of 9.45 mol of aluminum oxide (Al2O3)? – First add up all the masses • Al = 27g x 2 = 54g • O = 16g x 3 = 48g • Al2O3 = 102 g – Then convert from moles to grams: • 9.45 mol Al2O3 x (102g/1 mol Al2O3) = 963.9g The Mole-Mass Relationship Practice • 16. Find the mass, in grams, of 4.52 x 10-3 mol C20H42. The Mole-Mass Relationship Practice • 17. calculate the mass, in grams, of 2.50 mol of iron(II) hydroxide Fe(OH)2. The Mole-Mass Relationship Practice • You can calculate the number of moles using the same relationship you use to find the mass of moles by inverting the conversion factor. • Moles = mass x (1mole/mass) The Mole-Mass Relationship Practice • How many moles of iron(III) oxide are contained in 92.2 g of pure Fe2O3? • Fe2O3 = 159.6 g = 1 mol • 92.2 g Fe2O3 x (1 mol/159.6 g Fe2O3) = 0.578 mol Fe2O3 The Mole-Mass Relationship Practice • 18. Find the number of moles in 3.70 x 10-1 g boron. The Mole-Mass Relationship Practice • 19. Calculate the number of moles in 75.0 g of dinitrogen trioxide (N2O3) The Mole-Volume Relationship • Avogadro’s hypothesis states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles. • Because of variations due to temperature and pressure, the volume of a gas is usually measured at a standard temperature and pressure. The Mole-Volume Relationship • Standard temperature and pressure (STP) means a temperature of 0C and a pressure of 101.3 kPa, or 1 atmosphere (atm). The Mole-Volume Relationship • At STP, 1 mol or 6.02 x 1023 representative particles, of any gas occupies a volume of 22.4 L. • The quantity, 22.4 L, is called the molar volume of a gas. The Mole-Volume Relationship • The molar volume is used to convert a known number of moles of gas to the volume of the gas at STP. • Volume of gas = moles of gas x (22.4L/1mol) The Mole-Volume Relationship • Determine the volume, in liters, of 0.60 mol SO2 gas at STP. • 1 mol SO2 = 22.4 L SO2 • Volume = 0.60 mol SO2 x (22.4L/1mol) • = 13 L SO2 The Mole-Volume Relationship - Practice • 20. What is the volume of these gases at STP? – A. 3.20 x 10-3 mol CO2 – B. 3.70 mol N2 The Mole-Volume Relationship - Practice • 21. at STP, what volume do these gases occupy? – A. 1.25 mol He – B. 0.335 mol C2H6 Calculating Molar Mass from Density • Different gases have different densities. Density of a gas is measured in grams per liter (g/L) and at a specific temperature. • Molar mass = (grams/L) x (22.4 L/1 mole) Calculating Molar Mass from Density • The density of a gaseous compound containing carbon and oxygen is found to be 1.964 g/L at STP. What is the molar mass of the compound? • Molar mass = (1.964 g/L) x (22.4 L/1 mol) • = 44 g/mol Calculating Molar Mass from Density - Practice • 22. a gaseous compound has a density of 3.58 g/L at STP. What is the molar mass of this gas? Calculating Molar Mass from Density • 23. What is the density of krypton gas at STP?
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