3Example: Calculate the molar mass (gram molecular weight) of a mole of iodine, I2. Unit for molar massI = 126.9(2) = 253.8From the formula of the compoundFrom the mass off of the periodic table.
4---------------------------------------- add together = 342.17 Example: Calculate the molar mass of a mole of aluminum sulfate (Al2(SO4)3).From the masses off of the periodic table.From the formula of the compoundAl = (2) = 53.96S = (3) = 96.21O = (12) =add together =Unit for molar mass
13Example: What is the volume, in liters, of a 2 Example: What is the volume, in liters, of a 2.00 mole sample of methane (CH4) at STP?44.8 LCH422.4 L/mol2.00 molXThe number of liters in one mole is always 22.4From the problem
14Example: How many moles of ethane (C2H6) are there in 5 Example: How many moles of ethane (C2H6) are there in 5.60 liters of ethane?From the problem5.6 LC2H622.4 L/mol0.25 mol÷The number of liters in one mole is always 22.4
16Molar mass is g/mol and you find grams from the periodic table. We’ve done problems of one step. Moles to a unit or unit to moles. Now we can do multi step problems using this picture to help us see where we need to go next.This picture is a summary of all of the problems we have done up to this point along with helpful hints to units and numbers. The better you understand this the easier mole conversions will be.
17Example: What would be the volume in liters of 40 Example: What would be the volume in liters of grams of neon at STP?From the problemFrom the periodic table40.36 gNe20.18 g/mol2.00 mol44.8 LNe22.4 L/mol2.00 mol÷XThe number of liters in one mole is always 22.4We’re not to liters yet…
1856 L 1.505x1024 mcl CO2 CO2 22.4 L/mol 6.02x1023 mcl/mol 2.5 mol Example: How many molecules would there be in 56 liters of carbon dioxide at STP?From the problemThe number of liters in one mole is always 22.456 LCO222.4 L/mol2.5 mol1.505x1024 mclCO26.02x1023 mcl/mol2.5 mol÷XThe number of atoms/molecules in one mole is always 6.02x1023We’re not to molecules yet…
20Example: Calculate the percent composition of sodium hydrogen carbonate (NaHCO3)? Step 1 – find molar mass of the compound.Step 2 – divide mass of each element by molar mass.Step 3 – multiply answers by 100%.Molar Mass CalculationNa = (1) = 22.99H = 1.01 (1) = 1.01C = (1) = 12.01O = 16.00(3) = 48.00= g/mol
21Example: Which pair of molecules has the same empirical formula? Molecular formulaEmpirical formulaC2H4O2c) NaCrO4C6H12O6d) Na2Cr2O7CH2OCH2OThese two can not be “reduced”.An empirical formula is similar to a reduced fraction.
22Example: Calculate the empirical formula for a compound with 67 Example: Calculate the empirical formula for a compound with 67.6% Hg, 10.8% S, 21.6% O?Step 1 – change percents to grams (assume we have 100 gram sample then percents are the number of grams).Step 2 – change the grams to moles.Step 3 – divide all answers by the smallest number (of the answers).Step 4 – the results become the subscripts for the formula.Step 4HgSO4Step 1Step 2Step 3÷÷
23Example: Find the molecular formula of ethylene glycol, which is used as antifreeze. The molecular mass is 62g/mol and the empirical formula is CH3O?Step 1 – Find the empirical formula mass (EFM)Step 2 – Divide the molar mass (from problem) by the EFM to get the multiplier.Step 3 – Use the multiplier to determine the subscripts by multiplying each subscript by the multiplier.Step 3C2H6O2Step 1 EFM CalculationC = (1) = 12.01H = 1.01 (3) = 3.03O = 16.00(1) = 16.00=31.04 g/molStep 2MULTIPLIER