 # Wednesday, March 19 th : “A” Day Thursday, March 20 th : “B” Day Agenda  Collect Homework: pg. 21/22 practice worksheet  Continue Section 7.1: “Avogadro’s.

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Wednesday, March 19 th : “A” Day Thursday, March 20 th : “B” Day Agenda  Collect Homework: pg. 21/22 practice worksheet  Continue Section 7.1: “Avogadro’s Number & Molar Conversions”  Homework : “Grams/Moles Calculations” worksheet Concept Review: “Avogadro’s Number & Molar Conversions”: #6-10

Continue 7.1: “Avogadro’s Number and Molar Conversions” 6.022 X 10 23 atoms 1 mole

Molar Mass Links 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 (H 2 O, CH 4, etc. ) and diatomic elements. (O 2, F 2, etc.) ** The units for molar mass are ** grams/mole

Molar Mass Example #1  What is the molar mass of water, H 2 O? 1.Use the period table to find the atomic mass of each element in the compound. 2.Add them up to get the molar mass of the compound: H = 2(1.01 g/mol) O = 16.00 g/mol Molar mass of water = 18.02 g/mol

Molar Mass Example #2  What is the molar mass of sulfuric acid, H 2 SO 4 ? H = 2(1.01 g/mol) S = 32.07 g/mol O = 4(16.00 g/mol) Molar mass of sulfuric acid = 98.09 g/mol

Molar Mass Example #3  What is the molar mass of sodium carbonate, Na 2 CO 3 ? Na = 2(22.99 g/mol) C = 12.01 g/mol O = 3(16.00 g/mol) Molar mass of sodium carbonate = 105.99 g/mol

So, why do we need to know the molar mass…  Molar mass can be used as a conversion factor to change from mass (in grams) to amount (in moles) !!

Changing Moles Mass (in grams)  Determine the mass in grams of 3.50 mol of copper, Cu. 1.Start with what you know: 3.50 mol Cu 2.Use the molar mass of Cu as the conversion factor to change mol Cu grams Cu. 3.50 mol Cu X 63.55 g Cu = 222 g Cu 1 mol Cu (3 sig figs)

Changing Moles Mass (in grams) Example #1  What is the mass in grams of 10.5 mol ammonia, NH 3 ? 1.Start with what you know: 10.5 mol NH 3 2.Use the periodic table to calculate the molar mass of NH 3 to use as a conversion factor: N: 14.01 g/mol H: 3(1.01) g/mol 17.04 g/mol

Changing Moles Mass (in grams) Example #1, cont. 3. Multiply by the conversion factor to change mol NH 3 grams NH 3. 10.5 mol NH3 X 17.04 g NH 3 = 179 g NH 3 1 mol NH 3 (3 sig figs)

Changing Moles Mass (in grams) Example #2  How many grams are in 1.26 moles of aluminum hydroxide, Al(OH) 3 ? 1.Start with what you know: 1.26 moles Al(OH) 3 2.Use the periodic table to calculate the molar mass of Al(OH) 3 to use as a conversion factor: Al: 26.98 g/mol O: 3(16.00 g/mol) H: 3(1.01 g/mol) 78.01 g/mol

Changing Moles Mass (in grams) Example #2, cont. 3.Multiply by the conversion factor to change mol Al(OH) 3 grams Al(OH) 3. 1.26 mol Al(OH) 3 X 78.01 g Al(OH) 3 = 1 mole Al(OH) 3 98.3 g Al(OH) 3 (3 sig figs)

Do you think we can go the other way and change mass in grams to amount in moles..  Of course we can, and that’s what we’re going to do…

Changing Mass (in grams) Moles  How many moles of helium are contained in 0.255 g He? 1.Start with what you know: 0.255 g He 2.Use the molar mass of He as the conversion factor to change mass He mol He 0.255 g He X 1 mole He =.0638 mol He 4.00 g He (3 sig figs)

Changing Mass (in grams) Moles Example #1  How many moles are there in 68 g of copper (II) hydroxide, Cu(OH) 2 ? 1.Start with what you know: 68 g Cu(OH) 2 2.Use the periodic table to calculate the molar mass of Cu(OH) 2 to use as a conversion factor: Cu: 63.55 g/mol O: 2(16.00 g/mol) H: 2(1.01 g/mol) 97.57 g/mol

Changing Mass (in grams) Moles Example #1, cont. 3.Multiply by the conversion factor to change mol Cu(OH) 2 grams Cu(OH) 2. 68 g Cu(OH) 2 X 1 mol Cu(OH) 2 = 97.57 g Cu(OH) 2.70 mol Cu(OH) 2 (2 sig figs)

Changing Mass (in grams) Moles Example #2  How many moles are there in 1,200 g of ammonia, NH 3 ? 1.Start with what you know: 1,200 g NH 3 2.Use the periodic table to calculate the molar mass of NH 3 to use as a conversion factor: N: 14.01 g/mol H: 3(1.01 g/mol) 17.04 g/mol

Changing Mass (in grams) Moles Example #2, cont. 3.Multiply by the conversion factor to change grams NH 3 moles NH 3. 1,200 g NH 3 X 1 mol NH 3 = 17.04 g NH 3 70. mol NH 3 (2 sig figs)

Homework  You may work with a partner to complete the “Grams/Moles Calculations” worksheet.  You must show all work to get credit!

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