Chapter 6 Chemical Reactions and Quantities 6.5 Molar Mass

Molar Mass The molar mass is the mass of one mole of a substance the atomic mass of an element expressed in grams

Learning Check Give the molar mass to the nearest 0.1 g. A. K = ________ B. Sn = ________

Solution Give the molar mass to the nearest 0.1 g. A. K = 39.1 g B. Sn = 118.7 g

Molar Mass of CaCl2 For a compound, the molar mass is the sum of the molar masses of the elements in the formula. We calculate the molar mass of CaCl2 to the nearest 0.1 g as follows. 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 Determine the molar mass of K3PO4 to 0.1 g. K 3 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

One-Mole Quantities 32.1 g 55.9 g 58.5 g 294.2 g 342.3 g

Guide to Calculating Molar Mass

Learning Check Calculate the molar mass for Al(OH)3 to the nearest 0.1g. 1) 44.0 g/mole 2) 75.0 g/mole 3) 78.0 g/mole

Solution STEP 1 Obtain the molar mass of each element. Al 27.0 g/mole O 16.0 g/mole H 1.0 g/mole STEP 2 Multiply each by the subscript in the formula. 1 mole Al x 27.0 g Al = 27.0 g 1 mole Al 3 moles O x 16.0 g O = 48.0 g 1 mole O 3 moles H x 1.0 g H = 3.0 g 1 mole H STEP 3 Total: 1 mole of Al(OH)3 = 78.0 g (3)

Learning Check Prozac, C17H18F3NO, is an antidepressant that inhibits the uptake of serotonin by the brain. What is the molar mass of Prozac? 1) 40.0 g/mole 2) 262 g/mole 3) 309 g/mole

Solution 3) 309 g/mole STEP 1 Obtain the molar mass of each element. C 12.0 g/mole H 1.0 g/mole F 19.0 g/mole N 14.0 g/mole O 16.0 g/mole STEP 2 Multiply each by the subscript in the formula. 17 moles C x 12.0 g C = 204 g 1 mole C 18 moles H x 1.0 g H = 18 g 1 mole H

Solution (continued) STEP 2 (continued) 3 moles F x 19.0 g F = 57.0 g 1 mole F 1 mole N x 14.0 g N = 14.0 g 1 mole N 1 mole O x 16.0 g O = 16.0 g 1 mole O STEP 3 Total: 1 mole of C17H18F3NO = 309 g

Conversion Factors from Molar Mass Methane (CH4), known as natural gas, is used in gas stoves and gas heaters. 1 mole of CH4 = 16.0 g of CH4 The molar mass of methane can be written as 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 an equality and two molar mass conversion factors for acetic acid.

Solution Acetic acid, C2H4O2, gives the sour taste to vinegar. Write an equality and two molar mass conversion factors for acetic acid. Equality: 1 mole of acetic acid = 60.0 g of acetic acid Molar mass conversion factors: 1 mole acetic acid and 60.0 g acetic acid 60.0 g acetic acid 1 mole acetic acid

Guide to Calculations Using Molar Mass

Calculating Grams from Moles Aluminum is often used for the structure of lightweight bicycle frames. How many grams of Al are in 3.00 moles of Al? 3.00 moles Al x 27.0 g Al = 81.0 g of Al 1 mole Al mole factor for Al

Learning Check The artificial sweetener aspartame (NutraSweet), C14H18N2O5 , is used to sweeten diet foods, coffee, and soft drinks. How many moles of aspartame are present in 225 g of aspartame?

Solution STEP 1 Given: 225 g of aspartame, C14H18N2O5 STEP 2 Plan: g of aspartame moles of aspartame STEP 3 Determine molar mass of aspartame: 14(12.0) + 18(1.0) + 2(14.0) + 5(16.0) = 294 g/mole STEP 4 Set up problem to calculate the moles of aspartame: 225 g aspartame x 1 mole aspartame 294 g aspartame mole factor (inverted) = 0.765 mole of aspartame

Converting Between Mass, Moles, and Particles