Thursday, April 7th : “A” Day Friday, April 8th: “A” Day Agenda Finish Section 7.1: “Avogadro’s Number & Molar Conversions” In-Class: Practice pg. 231: #1-4 Practice pg. 232: #1-3 Concept Review: “Avogadro’s Number & Molar Conversions”: #6-10 Section 7.1 quiz next time…

Finish 7.1: “Avogadro’s Number and Molar Conversions” 6.022 X 1023 atoms 1 mole

Molar Mass Relates Moles to Grams Molar mass: the mass in grams of one mole of an element or compound. Molar mass is numerically equal to the atomic mass of elements (Fe, Al, etc.) and the formula mass of compounds (H2O, CH4, etc. ) and diatomic elements. (O2, F2, etc.) The units for molar mass are grams mole

Molar mass of water = 18.02 g H2O Molar Mass Example #1 What is the molar mass of water, H2O? To determine the molar mass, look up the atomic mass of each element present in the compound and add them up. This is the molar mass. H = 1.01 g/mol O = 16.0 g/mol Molar mass of water = 18.02 g H2O 1 mole

Molar Mass Example #2 What is the molar mass of sulfuric acid, H2SO4? H = 1.01 g/mol S = 32.07 g/mol O = 16.0 g/mol Molar mass of sulfuric acid = 98.09 g H2SO4 1 mole

So, why do we need to know the molar mass… Molar mass can be used as a conversion factor in problems converting between mass and amount!!!

Converting Number of Particles to Mass To convert from number of particles to mass, you must use a two-step process: First, convert number of particles to amount in moles using Avogadro’s number. Second, convert amount in moles to mass in grams using the molar mass. Two different conversion factors must be used!

Converting Between Mass, Amount, and Number of Particles

Sample Problem C, pg. 231 Converting Number of Particles to Mass Find the mass in grams of 2.44 X 1024 atoms of carbon, whose molar mass is 12.01 g/mol. Known: 2.44 X 1024 atoms of carbon Unknown: Mass in grams of carbon Two conversion factors: 1 mole C AND 12.01 g C 6.022 X 1023 atoms C 1 mole C

Sample Problem C, continued Converting Number of Particles to Mass Step 1: Convert # of particles amount in moles: 2.44 X 1024 C atoms X 1 mole C 6.022 X 1023 atoms C = 4.05 moles C Step 2: Convert amount in moles mass (in grams) 4.05 moles C X 12.01 g C 1 mole C = 48.6 g C

Additional Practice Find the mass in grams of 6.12 X 1014 formula units of rhenium dioxide, ReO2, 218.21 g/mol. Known: 6.12 X 1014 formula units ReO2 Unknown: Mass in grams of ReO2 Two conversion Factors: 1 mole ReO2 AND 218.21 g ReO2 6.022 X 1023 form unit ReO2 1 mole ReO2

= 2.23 X 10 -7 g ReO2 Additional Practice Step 1: Convert # of particles amount in moles: 6.12 X 1014 form. unit X _1 mol_ReO2__ 6.022 X 1023 form. unit ReO2 = 1.02 X 10 -9 mole ReO2 Step 2: Convert amount in moles mass (in grams) 1.02 X 10 -9 mole ReO2 X 218.21 g ReO2 1 mole ReO2 = 2.23 X 10 -7 g ReO2

Converting Mass to Number of Particles Converting from mass to number of particles is simply the opposite of the previous problems. To convert from mass to number of particles, you must use a two-step process: First, convert mass in grams to amount in moles using molar mass. Second, convert amount in moles to number of particles using Avogadro’s number. Two different conversion factors must be used!

Sample Problem D, pg. 232 Converting Mass to Number of Particles Find the number of molecules present in 47.5 g of glycerol, C3H8O3. The molar mass of glycerol is 92.11 g/mol. Known: 47.5 g glycerol, C3H8O3 Unknown: # of molecules present Two conversion factors: 1 mole C3H8O3 AND 6.022 X 1023 molecules C3H8O3 92.11 g C3H8O3 1 mole C3H8O3

Sample Problem D, cont. Converting Mass to Number of Particles Step 1: Convert mass (in grams) amount in moles: 47.5 g C3H8O3 X 1 mole C3H8O3 = 0.516 mol C3H8O3 92.11 g C3H8O3 Step 2: Convert amount in moles # of molecules: 0.516 mol C3H8O3 X 6.022 X 1023 molecules C3H8O3 1 mole C3H8O3 = 3.11 X 1023 molecules C3H8O3

Additional Practice Determine the number of atoms present in 54.3 grams of cobalt, Co. Known: 54.3 g of cobalt, Co. Unknown: # of atoms Two conversion Factors: 1 mole Co AND 6.022 X 1023 atoms Co 58.93 g Co 1 mole Co

= 5.55 X 1023 atoms Co Additional Practice Step 1: Convert mass (in grams) amount in moles: 54.3 g Co X 1 mol Co = 0.921 mol Co 58.93 g Co Step 2: Convert amount in moles # of atoms: 0.921 moles Co X 6.022 X 1023 atoms Co 1 mole Co = 5.55 X 1023 atoms Co

In-Class Assignments/Homework You Must SHOW WORK! Practice pg. 231: #1-4 Practice pg. 232: #1-3 Concept Review: “Avogadro’s Number & Molar Conversions”: #6-10 Section 7.1 quiz next time…