 # An Introduction to MOLAR MASS Section 5 2

• Slides: 13 An Introduction to MOLAR MASS Section 5. 2 MOLAR MASS n Definition: The mass in grams of 1 mol of a substance n Symbol: M or mm n Unit: g/mol Molar Mass of Atoms n n Molar mass = Mass off the periodic table (atomic mass), in grams Means that 1 mole of an element IS its atomic mass. MOLAR MASS vs ATOMIC MASS Element Atomic Mass Molar Mass Hydrogen 1. 01 µ 1. 01 g/mol Sodium 22. 99 µ 22. 99 g/mol Gold 196. 97 µ 196. 97 g/mol Indicates that 1 mole of gold Masses 196. 97 g MOLAR MASS (M) OF COMPOUNDS To find Molar mass (M) of a compound n Need molar mass (M) of each individual element in the compound ELEMENTS (atoms) make COMPOUNDS (molecules) CALCULATING M of compound n Ex 1: Calculate the M of H 2 O = molar mass of H + molar mass of O = 2(1. 01 g/mol) + 16. 00 g/mol = 2. 02 g/mol + 16. 00 g/mol = 18. 02 g/mol CALCULATING M of compound n Ex 2: Calculate the M of Be. O = MBe + MO =9. 01 g/mol + 16. 00 g/mol = 25. 01 g/mol CALCULATING M of compound n Ex 3: Calculate the M of Ca 3(PO 4)2 = MCa + MP + MO = 3(40. 08) + 2(30. 97) + 8 (16. 00) = 310. 18 g/mol CONVERTING MASS TO MOLES Divide by M n n Mass (g) Moles (mol) n=m M Where n = moles (mol) m = mass (g) M = molar mass (g/mol) CONVERTING MASS TO MOLES n Example 1 : How many moles of CH 3 COOH are in a 236 g sample? CONVERTING MOLES TO MASS Multiply By M MOLES (mol) n Mass (g) m=nx. M Where n = moles (mol) m = mass (g) M = molar mass (g/mol) CONVERTING MOLES TO MASS Example 2: What is the mass of 5. 67 x 1024 molecules of cobalt (II) chloride n HOMEWORK n n Page 235 # 31 -40 Page 237 # 41 -50 Page 239 # 51 -60 Page 242 # 61 -70