 # Unit 5 The Mole Molar Mass The sum

• Slides: 13 Unit 5: The Mole Molar Mass • The sum of the atomic masses of all the atoms in the formula of a compound or molecule Calculating Molar Mass • Calculate the molar mass for H 2 O: – H = 2 x 1. 0079 g = 2. 0158 g – O = 1 x 15. 999 g = 15. 999 g Molar mass of water = 18. 0148 g • Calculate the molar mass for Fe 2(SO 4)3: – Fe = 2 x 58. 847 g = 117. 694 g – S = 3 x 32. 06 g = 96. 18 g – O = 12 x 15. 999 g = 191. 988 g Molar mass of iron (III) sulfate = 405. 862 g Practice!!! The Mole • A counting word, just like a dozen – A dozen = 12 – A mole = 6. 02 x 1023 • Two moles of marbles = 2 x 6. 02 x 1023 • Three moles of hair pins = 3 x 6. 02 x 1023 • 6. 02 x 1023 also known as Avogadro’s # – Amedeo Avogadro (Italian Scientist) aided in this development Mole Conversion Factor Molar mass (g) of substance = 6. 02 x 1023 molecules of substance = 1 mole of substance Mole Conversion Factor Possibilities • 1 mole molar mass (g) • molar mass (g) 1 mole • 1 mole 6. 02 x 1023 atoms or molecules • 6. 02 x 1023 atoms or molecules 1 mole Mole Conversion Factor Possibilities • molar mass (g) 6. 02 x 1023 atoms or molecules • 6. 02 x 1023 atoms or molecules molar mass (g) v Use the word atoms when describing a single element; use the word molecule when describing molecules and compounds Mole Conversion Examples Molar mass = Avogadro’s # = 1 mole 18. 0148 g of H 2 O = 6. 02 x 1023 molecules of H 2 O = 1 mole of H 2 O 405. 862 g of Fe 2(SO 4)3 = 6. 02 x 1023 of Fe 2(SO 4)3 = 1 mole of Fe 2(SO 4)3 6. 941 g of Li = 6. 023 x 1023 atoms of Li = 1 mole of Li Mole Conversion Practice Problem 1 • If 5, 000 chlorine atoms are used to disinfect water, how many moles is that? 5, 000 atoms Cl x 1 mole Cl = 8. 3 x 1023 mole Cl 6. 02 x 1023 atoms Cl 8. 3 x 1023 mole Cl 8 x 1023 mole Cl Correct Sig Fig Mole Conversion Practice Problem 2 • Thirty moles of carbon monoxide could be a lethal amount. How many grams is that? 30 moles CO x 28. 01 g of CO = 840. 3 g of CO 1 mole CO 840. 3 g CO 800 g CO Correct Sig Fig Mole Conversion Practice Problem 3 • One liter of water weighs 1, 000 g. How many water molecules is that? 1, 000 g H 2 O x 1 mole H 2 O x 6. 02 x 1023 molecules H 2 O = 3. 3 x 1023 molecules H 2 O 18. 0148 g H 2 O 1 mole H 2 O 3. 3 x 1023 molecules H 2 O Correct Sig Fig Practice!!!