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The Mole

Molar Mass Calculating Molar Mass Also called atomic mass, formula mass, molecular mass Unit = g/mol Calculating Molar Mass Use the average atomic mass from the periodic table For atoms = atomic mass Ex. C = 12.011 g/mol Fe = 55.847 g/mol For compounds = sum of the atomic masses of the atoms that are in the formula EX: CaI2 = 40.078 g/mol + 2 (126.904) g/mol = 293.886 g/mol EX: (NH4)3PO4 = 3(14.007) + 12(1.0079) + 30.974 + 4(15.999) = 149.086 g/mol

The Mole Mole = the SI unit for how much of a substance or amount How do you measure how much you have? Counting (impractical – too many particles) Weighing Volume Particles cannot be counted directly, but we need to know how many particles are there. In chemistry we use the mole to figure out how many particles there are when we weigh something or measure the volume of something. Mole = the SI unit for how much of a substance or amount The mole is a unit similar to dozen- just many more than 12 It tells you how many you have.

The Mole 1 dozen = 12 1 gross = 144 1 ream = 500 1 mole = 6.02 x 1023 There are exactly 12 grams of carbon-12 in one mole of carbon-12.

Particles  moles or moles  particles Use Avogadro’s Number = 1 mole = 6.02 X1023 particles (atoms, molecules, formula units) *FOR ANY SUBSTANCE Grams  moles or moles  grams Use the molar mass from the periodic table. Liter  moles or moles  liter For Gases at STP (standard temperature and pressure) 1 mole = 22.4 L

I didn’t discover it. Its just named after me! Avogadro’s Number 6.02 x 1023 is called “Avogadro’s Number” in honor of the Italian chemist Amadeo Avogadro (1776-1855). I didn’t discover it. Its just named after me! Amadeo Avogadro

Calculating Formula Mass Calculate the formula mass of carbon dioxide, CO2. 12.01 g + 2(16.00 g) = 44.01 g  One mole of CO2 (6.02 x 1023 molecules) has a mass of 44.01 grams

Avogadro’s Number 602,214,000,000,000,000,000,000 Avogadro’s # of sheets of paper stacked one sheet on top of another would reach beyond our solar system. Avogadro’s # of basketballs could create a new planet the size of Earth. Avogadro’s # of grains of rice would cover the land masses of the Earth to a depth to 75 meters. Avogadro’s # of pennies. You decided to give away $1 million dollars a day to every person on Earth , it would take more than 3000 years to distribute all of your money

Mole Relationships Liters Mole Grams Atoms or molecules 6.02 x 1023 Atomic Mass Grams

Particles Mole Mass (g) Molar Mass Avogadro’s Number 22.4 L/mol Particles Atoms Molecules f.u. Mole Mass (g) Volume (L)

Particles atoms, molecules, or formula units Mass Volume (Gas at STP) Molar Mass 22.4 Avogadro’s Number Mole Conversions

Calculations with Moles: Converting moles to grams How many grams of lithium are in 3.50 moles of lithium? 3.50 mol Li 6.94 g Li = g Li 24.3 1 mol Li

Calculations with Moles: Converting grams to moles How many moles of lithium are in 18.2 grams of lithium? 18.2 g Li 1 mol Li = mol Li 2.62 6.94 g Li

Calculations with Moles: Using Avogadro’s Number How many atoms of lithium are in 3.50 moles of lithium? 3.50 mol 6.02 x 1023 atoms = atoms 2.07 x 1024 1 mol

Calculations with Moles: Using Avogadro’s Number How many atoms of lithium are in 18.2 g of lithium? 18.2 g Li 1 mol Li 6.022 x 1023 atoms Li 6.94 g Li 1 mol Li (18.2)(6.022 x 1023)/6.94 = atoms Li 1.58 x 1024

Try these on your own!!! ? g = 8 mol Al2(SO4)3 Ex. How many moles are in 8.04*1024 atoms Fe? ? g = 8 mol Al2(SO4)3

Calculations with Moles: Using Standard Molar Volume How many moles of hydrogen are in 100 L of hydrogen at STP? 100 L 1 mol = mol 4.64 22.4 L

Calculations with Moles: Using Standard Molar Volume How many liters are occupied by 3 moles of oxygen gas at STP? 3 mol 22.4 L = L 67.2 1 mol

Try These!! How many atoms are in 20.04 g Sn? How many liters are equal to 8 moles of CO2? How many moles are equal to 2.4 L of O2? How many grams of O2 are in 2.4 L O2?

*Within a formula, subscripts can be considered as the: Atom & Mole Ratios *Within a formula, subscripts can be considered as the: # of atoms within molecules of the compound the # of moles of that element within moles of the compound. (Since avogadro’s # cancels out)

% Composition Total Mass Percent Composition = The % by mass of each element in a compound. Mass of part X 100 = % composition Total Mass Example: Find the % of Al composition of Al2(SO4)3 *If you had 25.0 grams of this substance, How much would be Al?

Ex: Na2CO310H2O . Find the % of water in this hydrate. EX: Find the % composition of a compound containing tin and chlorine if 18.35 g of the compound contains 5.74 g of tin.

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Molecular/Empirical Formula Empirical Formula = smallest whole number ratio of moles of the elements in a compound Molecular Formula = actual number and kinds of atoms present in a compound Ex. Molec Formula = N10O5 Emp Formula = N2O

Calculating Empirical Formula An empirical formula is a ratio of moles of each atom in a compound. Must have the moles of each atom. *If you are given %, assume that you have 100 grams of the substance then Convert grams to moles. To find the lowest whole number ratio (mole ratio). Divide each # of moles by the smallest # of moles. If a # in the ratio is .5 (.4 - .6), double everything. Apply ratio to atoms given as subscripts.

To Repeat Find Moles *If you are given %, assume that you have 100 grams Divide each # of moles by the smallest # of moles. If the ratio is .5 (.4 - .6), double everything. Apply ratio as subscripts.

25.9 grams N and 74.1 grams O 25.9 / 14 = 1.85 74.1 / 16 = 4.631

Calculating Molecular Formula Calculate the empirical formula mass (efm) Divide a given molar mass (molecular mass) by efm Gives you the number of emp. form. in your molecular formula Multiply the emp. form. by that # Ex. EF = CH4N Molar Mass = 60 g/mol

EX: EF = NO2 Molar Mass = 138 g/mol Ex. 27.59 %C, 1.15 %H, 16.09 %N, 55.17 %O Molar mass = 261.1 g/mol. Find molecular formula