Chapter 5 Chemical Reactions and Quantities 5.6 Molar Mass

Molar Mass The molar mass is the mass of one mole of an element or compound. is the atomic mass expressed in grams. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Molar Mass from Periodic Table Molar mass is the atomic mass expressed in grams. 1 mole Ag 1 mole C 1 mole S = 107.9 g = 12.01 g = 32.07 g

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

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

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 One-mole Quantities 32.1 g 55.9 g 58.5 g 294.2 g 342.2 g

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 mole K (39.1 g/mole) + 1 mole O (16.0 g/mole) 78.2 g + 16.0 g = 94.2 g B. Al(OH)3 78.0 g/mole 1 mole Al (27.0 g/mole) + 3 mol O (16.0 g/mole) + 3 mol 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 + 18.2 + 57.0 + 14.0 + 16.0 = 309 g/mole

Molar Mass Factors Molar mass conversion factors are written from molar mass. relate grams and moles of an element or compound. Example: Write molar mass factors for methane, CH4, used in gas stoves and gas heaters. Molar mass: 1 mol CH4 = 16.0 g 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.

Solution Acetic acid C2H4O2 gives the sour taste to vinegar. Calculate molar mass: 24.022 + 4.032 + 31.998 = 60.0 g/mole 1 mole of acetic acid = 60.052 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 Moles Grams

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

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 mole C6H10S

Grams, Moles, and Particles A molar mass factor and Avogadro’s number convert grams to particles. molar mass Avogadro’s number g mole particles particles to grams. Avogadro’s molar mass particles mole g

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

Solution How many H2O molecules are in 24.0 g 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 one 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 one 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 C6H10S