 # Molar Mass = mass in grams of one mole –Units grams/mole For elements, molar mass = atomic mass Why aren’t all atomic masses whole numbers? –Remember that.

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Molar Mass = mass in grams of one mole –Units grams/mole For elements, molar mass = atomic mass Why aren’t all atomic masses whole numbers? –Remember that atomic masses are averages of all the isotopes H 1 C 12 O 16 Mg 24

Molar Mass of Compounds Add up the molar masses of each individual element in the compound Must multiply the atomic masses by the number of atoms for that element Example: BaCl 2 –Ba = 9.0 g/mol –Cl = 35 g/mol –So, MM = 1(9.0) + 2(35) = 79 g/mol

Calculate the molar mass HCl(think H 1 Cl 1 ) 1* 1.0 + 1* 35 = 36 g/mol Al 2 O 3 2 * 27.0 + 3 * 16.0 = 102 g/mol C 25 H 52 25 * 12.0 + 52 * 1.0 = 352 g/mol C 6 H 12 O 6 6 * 12.0 + 12 * 1.0 + 6 * 16.0 = 180 g/mol Mg(ClO 3 ) 2 1* 24 + 2 * 35 + 6 * 16 = 190 g/mol

Calculate the molar mass K 3 PO 4 212.3 g/mol Ca 3 (PO 4 ) 2 310.3 g/mol H 2 SO 4 98.1 g/mol (NH 4 ) 3 PO 4 149 g/mol BaSO 4 233.4 g/mol (NH 4 ) 3 Fe(CN) 6 265.8 g/mol

Find the Molar Mass BeF 2 47 g/mol K 3 P 148.3 g/mol (NH 4 ) 2 O 52 g/mol Al(OH) 3 78 g/mol Ca(NO 3 ) 2 164.1 g/mol LiNO 3 68.9 g/mol

Now we can use molar mass to convert between moles and grams Moles Mass (grams) ÷ molar mass x molar mass

Moles to Grams Conversion Reminders MUST first calculate molar mass for any conversion involving mass Use factor label method to perform conversion

Factor Label Steps

Example Conversions 1)2 moles C = ? Grams 2) 27 grams H 2 0 = ? Moles 3) 0.75 moles Al(OH) 3 = ? Grams 4) 475 grams Br 2 = ? moles

Now you try… 5) How many grams are in 2 moles of carbon? 6) How many moles are in 27 grams of water? 7) How many grams are in 0.75 moles of aluminum hydroxide? 8) How many moles are in 475 grams of bromine?

Now we can put two steps together to change from grams  particles Particles (atoms or molecules) Moles Mass (grams) ÷ molar mass x molar mass x Avogadro’s # ÷ Avogadro’s #

Particles to Grams Conversions Reminders MUST first calculate molar mass for any conversion involving mass Use factor label method to perform conversion

Factor Label Steps

Example Conversions 1)8.3 grams Ca = ? Atoms 2) 23 grams NaCl = ? formula units 3) 3.01 x 10 23 molecules Cl 2 = ? Grams 4) 1.204 x 10 24 formula units Al 2 O 3 = ? Grams 5) 88 grams CO 2 = ? Molecules 6) 4.32 x 10 23 formula units BaO = ? grams

Try these… 7) How many atoms are in 8.3 grams of calcium? 8) How many molecules are in 23 grams of sodium chloride? 9) How many formula units are in 88 grams of carbon dioxide? 10) What is the mass in grams of 3.01 x 10 23 atoms of chlorine? 11) What is the mass in grams of 1.204 x 10 24 molecules of aluminum oxide? 12) What is the mass in grams of 4.32 x 10 23 formula units of calcium oxide?

Complete in your notes showing your work! Determine the molar mass –K 3 PO 4 –Ca 3 (PO 4 ) 2 –HCl –H 2 O –BaSO 4 Calculate the moles –234 g NaCl –572 g MgCl 2 –23 g C 6 H 12 O 6 Calculate the mass –3.45 mol K –1.75 mol CO 2 –5.2 mol KNO 3 –4.48 mol Ca 3 (PO 4 ) 2 Don’t miss out on these easy points! Remember, there are no test or quiz retakes!!!!

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