Moles and Stoichiometry Chemical Reactions and Quantities Molar Mass Gram Formula Mass

Molar Mass The molar mass or gram formula mass is the mass in grams, 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

Solution Caffeine, the compound that basically keeps Mrs. Mannion alive, has the following formula: C8H10N4O2. What is the gram formula mass of Caffeine?

Learning Check Caffeine, the compound that basically keeps Mrs. Mannion alive, has the following formula: C8H10N4O2. What is the gram formula mass of Caffeine? C : 8 x 12.0 = 96.0 H: 10 x 1.0 = 10.0 N: 4 x 14.0 = 56.0 O: 2 x 16.0 = 32.0 194.0 g

Learning Check Prozac, C17H18F3NO, is an SSRI category of antidepressant that inhibits the re-uptake of serotonin by the brain. What is the molar mass of Prozac?

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

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 = 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

Moles and Volume For gases, there is another component relating volume and moles 1 mole of any substance takes up 22.4 liters of space 1 mole = 22.4 L of gas, no matter what the gas is, or what the formula mass of that gas may be

Example A sample of O2 takes up 33.6L. How many moles are present in the sample? Solution: 33.6L x 1 mole = 1.5 moles 22.4L

Example A sample of NH3 contains 3 moles. What is the volume of that gas? Solution: 3 moles NH3 x 22.4 L = 67.2 L 1 mole

Volume and Particles A sample of helium gas occupies11.2 liters. How many particles are in the sample? (are these particles atoms or molecules, and why?)

Volume and Particles A sample of NH3 occupies 7.5 L. How many particles are in the sample? (Are these particles atoms or molecules, and why?)

Summary