Chapter 5 Chemical Quantities and Reactions 5.2 Molar Mass Copyright © 2009 by Pearson Education, Inc.

Molar Mass The molar mass is the mass of 1 mole of an element or compound. is the atomic or molecular mass expressed in grams. Copyright © 2009 by Pearson Education, Inc.

Molar Mass from Periodic Table is the atomic mass expressed in grams. 1 mole of Ag 1 mole of C 1 mole of S = 107.9 g = 12.01 g = 32.07 g Copyright © 2009 by Pearson Education, Inc.

Learning Check Give the molar mass for each (to the tenths decimal place). A. 1 mole of K atoms = ________ B. 1 mole of Sn atoms = ________

Solution Give the molar mass for each (to the tenths decimal place). A. 1 mole of K atoms = 39.1 g B. 1 mole of Sn atoms = 118.7 g

Guide to Calculation Molar Mass of a Compound

Molar Mass of a Compound The molar mass of a compound is the sum of the molar masses of the elements in the formula. Example: Calculate the molar mass of CaCl2. Element Number of Moles Atomic Mass Total Mass Ca 1 40.1 g/mole 40.1 g Cl 2 35.5 g/mole 71.0 g CaCl2 111.1 g

Molar Mass of K3PO4 Calculate the molar mass of K3PO4. Element Number of Moles Atomic Mass Total Mass in K3PO4 K 3 39.1 g/mole 117.3 g P 1 31.0 g/mole 31.0 g O 4 16.0 g/mole 64.0 g K3PO4 212.3 g

Some 1-mole Quantities 32.1 g 55.9 g 58.5 g 294.2 g 342.2 g One-Mole Quantities 32.1 g 55.9 g 58.5 g 294.2 g 342.2 g Copyright © 2009 by Pearson Education, Inc.

Learning Check What is the molar mass of each of the following? A. K2O B. Al(OH)3

Solution A. K2O 94.2 g/mole 2 moles of K (39.1 g/mole) + 1 mole of O (16.0 g/mole) 78.2 g + 16.0 g = 94.2 g B. Al(OH)3 78.0 g/mole 1 mole of Al (27.0 g/mole) + 3 moles of O (16.0 g/mole) + 3 moles of H (1.01 g/mole) 27.0 g + 48.0 g + 3.03 g = 78.0 g

Learning Check Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 1) 40.1 g/mole 2) 262 g/mole 3) 309 g/mole

Solution Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 3) 309 g/mole 17 C (12.0) + 18 H (1.01) + 3 F (19.0) + 1 N (14.0) + 1 O (16.0) = 204 g C + 18.2 g H + 57.0 g F + 14.0 g N + 16.0 g O = 309 g/mole

Molar Mass Factors Molar mass conversion factors are fractions (ratios) written from the molar mass. relate grams and moles of an element or compound. for methane, CH4, used in gas stoves and gas heaters is 1 mole of CH4 = 16.0 g (molar mass equality) Conversion factors: 16.0 g CH4 and 1 mole CH4 1 mole CH4 16.0 g CH4

Learning Check Acetic acid, C2H4O2, gives the sour taste to vinegar. Write two molar mass conversion factors for acetic acid. Copyright © 2009 by Pearson Education, Inc.

Solution Calculate molar mass for acetic acid C2H4O2: 24.0 g C + 4.04 g H + 32.0 g O = 60.0 g/mole C2H4O2 1 mole of acetic acid = 60.0 g acetic acid Molar mass factors: 1 mole acetic acid and 60.0 g acetic acid 60.0 g acetic acid 1 mole acetic acid

Calculations Using Molar Mass Molar mass factors are used to convert between the grams of a substance and the number of moles. Molar mass factor Grams Moles

Moles to Grams Aluminum is often used to build lightweight bicycle frames. How many grams of Al are in 3.00 mole of Al? Molar mass equality: 1 mole of Al = 27.0 g of Al Setup with molar mass as a factor: 3.00 mole Al x 27.0 g Al = 81.0 g of Al 1 mole Al molar mass factor for Al

Learning Check Allyl sulfide, C6H10S, is a compound that has the odor of garlic. How many moles of C6H10S are in 225 g? Copyright © 2009 by Pearson Education, Inc.

Solution Calculate the molar mass of C6H10S. (6 x 12.0) + (10 x 1.01) + (1 x 32.1) = 114.2 g/mole Set up the calculation using a mole factor. 225 g C6H10S x 1 mole C6H10S 114.2 g C6H10S molar mass factor (inverted) = 1.97 moles of C6H10S

Grams, Moles, and Particles A molar mass factor and Avogadro’s number convert…

Learning Check How many H2O molecules are in 24.0 g of H2O? 1) 4.52 x 1023 H2O molecules 2) 1.44 x 1025 H2O molecules 3) 8.03 x 1023 H2O molecules

Solution How many H2O molecules are in 24.0 g of H2O? 3) 8.02 x 1023 24.0 g H2O x 1 mole H2O x 6.02 x 1023 H2O molecules 18.0 g H2O 1 mole H2O = 8.03 x 1023 H2O molecules

Learning Check If the odor of C6H10S can be detected from 2 x 10-13 g in 1 liter of air, how many molecules of C6H10S are present?

Solution If the odor of C6H10S can be detected from 2 x 10-13 g in 1 liter of air, how many molecules of C6H10S are present? 2 x 10-13 g x 1 mole x 6.02 x 1023 molecules 114.2 g 1 mole = 1 x 109 molecules of C6H10S are present