Jonathan Seibert PNHS - Chemistry The Mole Jonathan Seibert PNHS - Chemistry

How do we count things?

What happens when Too Small or Too Many?

A Mole How do we Count Things? 1 mole = 6.02 x 1023 1 dozen = 12 1 gross = 144 1 ream = 500 1 mole = 6.02 x 1023 A Mole

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

What is the Mole? 1 mole of hockey pucks would equal the mass of the moon! 1 mole of basketballs would fill a bag the size of the earth! 1 mole of pennies would cover the Earth 1/4 mile deep!

Molar Mass Mass of 1 mole of an element or compound. Atomic mass tells the... atomic mass units per atom (amu) grams per mole (g/mol)

Molar Mass Examples carbon aluminum zinc 12.01 g/mol 26.98 g/mol

Molar Mass Examples CO2 H2O NaCl 44.01 g/mol 18.02 g/mol 58.44 g/mol

The Mole Molar Conversions

Molar Conversions molar mass 6.02  1023 MOLES (g/mol) (particles/mol) IN GRAMS MOLES ATOMS (g/mol) (particles/mol)

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 1.8 moles of lithium? 1.8 mol Li 6.02 x 1023 atoms Li 1 mol Li (1.8)(6.02 x 1023)/1 = atoms Li 1.08 x 1024

Conversion Examples How many moles of carbon are in 26 g of carbon? 26 g C 1 mol C 12.01 g C = 2.2 mol C

Conversion Examples How many molecules are in 2.50 moles of C12H22O11? 6.02  1023 molecules 1 mol 2.50 mol = 1.51  1024 molecules C12H22O11

Molar Conversions molar mass 6.02  1023 MOLES (g/mol) (particles/mol) IN GRAMS MOLES ATOMS (g/mol) (particles/mol)

Conversion Examples Find the mass of 2.1  1024 atoms of Carbon. 1 mol 6.02  1023 atoms 12.01 g 1 mol = 42 g Carbon

Percentage Composition the percentage by mass of each element in a compound

Percentage Composition Find the % composition of Cu2S. 127.10 g Cu 159.17 g Cu2S %Cu =  100 = 79.9% Cu 32.06 g S 159.17 g Cu2S %S =  100 = 20.1% S

Percentage Composition Find the percentage composition of a sample that is 28 g Fe and 8.0 g O. 28 g 36 g %Fe =  100 = 78% Fe 8.0 g 36 g %O =  100 = 22% O

Percentage Composition How many grams of copper are in a 38.0-gram sample of Cu2S? Cu2S is 79.852% Cu (38.0 g Cu2S)(0.79852) = 30.3 g Cu

Percentage Composition Find the mass percentage of water in calcium chloride dihydrate, CaCl2•2H2O? 36.04 g 147.02 g %H2O =  100 = 24.51% H2O

C2H6 CH3 Empirical Formula Smallest whole number ratio of atoms in a compound C2H6 reduce subscripts CH3

Empirical Formula 1. Find mass (or %) of each element. 2. Find moles of each element. 3. Divide moles by the smallest # to find subscripts. 4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #’s.

Empirical Formula Find the empirical formula for a sample of 25.9% N and 74.1% O. 25.9 g 1 mol 14.01 g = 1.85 mol N = 1 N 1.85 mol 74.1 g 1 mol 16.00 g = 4.63 mol O = 2.5 O

N2O5 N1O2.5 Empirical Formula Need to make the subscripts whole numbers  multiply by 2 N2O5

CH3 C2H6 Molecular Formula “True Formula” - the actual number of atoms in a compound CH3 empirical formula ? C2H6 molecular formula

Molecular Formula 1. Find the empirical formula. 2. Find the empirical formula mass. 3. Divide the molecular mass by the empirical mass. 4. Multiply each subscript by the answer from step 3.

(CH2)2  C2H4 Molecular Formula empirical mass = 14.03 g/mol The empirical formula for ethylene is CH2. Find the molecular formula if the molecular mass is 28.1 g/mol? empirical mass = 14.03 g/mol 28.1 g/mol 14.03 g/mol = 2.00 (CH2)2  C2H4