Chapter 8

The Mole

1 trio = 3 singers

1 six-pack Cola = 6 cans Cola drink

1 dozen donuts = 12 donuts

1 gross of pencils = 144 pencils

Collection Terms

Contains 6.02 x 1023 particles

1 mole C = 6.02 x 1023 C atoms

1 mole H2O = 6.02 x 1023 H2O molecules

1 mole NaCl = 6.02 x 1023 Na+ ions and

6.02 x 1023 Cl– ions

A Moles of Particles

Moles of elements

1 mole Mg = 6.02 x 1023 Mg atoms

1 mole Au = 6.02 x 1023 Au atoms

Moles of compounds

1 mole NH3 = 6.02 x 1023 NH3 molecules

1 mole C9H8O4 = 6.02 x 1023 aspirin molecules

Examples of Moles

6.02 x 1023 particles 1 mole

or

1 mole

6.02 x 1023 particles

Avogadro’s Number

Suppose we invented a new collection unit called a mep. One mep contains 8 objects.

A. How many paper clips in 1 mep?1) 1 2) 4 3) 8

B. How many oranges in 2.0 meps?

1) 4 2) 8 3) 16

C. How many meps in 40 gummy bears?

1) 5 2) 10 3) 20

Learning Check

Suppose we invented a new collection unit called a mep. One mep contains 8 objects.

A. How many paper clips in 1 mep?3) 8

B. How many oranges in 2.0 meps?

3) 16

C. How many meps in 40 gummy bears?

1) 5

Solution

1. Number of atoms in 0.500 mole of Al1) 500 Al atoms

2) 6.02 x 1023 Al atoms3) 3.01 x 1023 Al atoms

2.Number of moles of S in 1.8 x 1024 S atoms1) 1.0 mole S atoms2) 3.0 mole S atoms3) 1.1 x 1048 mole S atoms

Learning Check

1. Number of atoms in 0.500 mol of Al3) 3.01 x 1023 Al atoms

0.500 mol Al x 6.02 x 1023 Al atoms1 mol Al

2. Number of moles of S if a sample of S contains 4.50 x 1024 S atoms2) 3.0 mole S atoms

4.50 x 1024 S atoms x 1 mol S

6.02 x 1023 S atoms

Solution

Number of grams in 1 mole Equal to the numerical value of the atomic

mass

1 mole of C atoms = 12.0 g

1 mole of Mg atoms = 24.3 g

1 mole of Cu atoms = 63.5 g

Molar Mass Determinatiom

Give the molar mass to 0.1 g

A. 1 mole of Br atoms = ________

B. 1 mole of Sn atoms =________

Learning Check

Give the molar mass to 0.1 g

A. 1 mole of Br atoms = 79.9 g/mole

B. 1 mole of Sn atoms = 118.7 g/mole

Solution

Mass in grams of 1 mole equal numerically to the sum of the atomic masses

1 mole of CaCl2 = 111.1 g/mole

(1 mole Ca x 40.1 g/mole) + (2 moles Cl x 35.5 g/mole)

1 mole of N2O4 = 92.0 g/mole

(2 moles N x 14.0 g/mole)+ (4 moles O x 16.0 g/mole)

Molar Mass of Compounds

A. 1 mole of K2O = ______g

B. 1 mole of antacid Al(OH)3 = ______g

Learning Check

A. 1 mole of K2O

(2 K x 39.1 g/mole) + (1 O x 16.0 g/mole) = 94.2 g

B. 1 mole of antacid Al(OH)3

(1 Al x 27.0 g/mole) + (3 O x 16.0 g/mole)

+ (3 x 1.0) = 78.0 g

Solution

Prozac, C17H18F3NO, is a widely used

antidepressant that inhibits the uptake of serotonin by the brain. It has a molar mass of

1) 40.0 g/mole

2) 262 g/mole

3) 309 g/mole

Learning Check

Prozac, C17H18F3NO, is a widely used

antidepressant that inhibits the uptake of serotonin by the brain. It has a molar mass of

3) 309 g/mole

17C (12.0) + 18H (1.0) + 3F (19.0) + 1N (14.0) + 1 O (16.0)

Solution

What is the percent carbon in C5H8NO4

(MSG monosodium glutamate), a compound used to flavor foods and tenderize meats?1) 8.22 %C2) 24.3 %C3) 41.1 %C

Learning Check

Molar mass = 146.0 g/mole% = total g C x 100

total g compound

= 60.0 g C x 100 = 41.1% C 146.0 g MSG

Solution

Methane CH4 known as natural gas is used in gas cook tops and gas heaters. Express the molar mass of methane in the form of conversion factors.

Molar mass of CH4 = 16.0 g

16.0 g CH4 and 1 mole CH4

1 mole CH4 16.0 g CH4

Molar Mass Factors

Acetic acid CH3COOH is the acid in vinegar .

It has a molar mass of 60.0 g/mole.

1 mole of acetic acid = ____________

1 mole acetic acid or g acetic acid

g acetic acid 1 mole acetic acid

Learning Check

Acetic acid CH3COOH is the acid in vinegar . It

has a molar mass of 60.0 g/mole.

1 mole of acetic acid = 60.0 g acetic acid

1 mole acetic acid or 60.0 g acetic acid

60.0 g acetic acid 1 mole acetic acid

Solution

molar mass Grams Moles

Calculations with Molar Mass

Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al?

3.00 moles Al ? g Al

Moles and Grams

1. Molar mass of Al 1 mole Al = 27.0 g Al

2. Conversion factors for Al 27.0g Al or 1 mol Al

1 mol Al 27.0 g Al

3. Setup 3.00 moles Al x 27.0 g Al 1 mole Al

Answer = 81.0 g Al

Mole Mass Conversions (grams moles)

The artificial sweetener aspartame

(Nutri-Sweet) formula C14H18N2O5 is

used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame?

Learning Check

1. Molar mass of Aspartame C14H18N2O5

(14 x 12.0) + (18 x 1.01) + (2 x 14.0) + (5 x 16.0) = 294 g/mole

2. Setup 225 g aspartame x 1 mole aspartame

294 g aspartame

= 0.765 mole aspartame

Solution

Atomic Mass

What is this number 35.34 for Cl??

The atomic mass - the average mass of all the isotopes (diff atoms) that make up a sample of chlorine

Chlorine consists of chlorine-35 and chlorine-37 in a 3:1 ratio

Average Mass is an average based on the percents of each of the isotopes present

Atomic Mass Calculation

Calculate the atomic mass of naturally occurring chlorine if 75.77% of chlorine atoms are chlorine-35 and 24.23% of chlorine atoms are chlorine-37

Step 1: convert the percentage to a decimal fraction:

0.7577 chlorine-35

0.2423 chlorine-37

Step 2

multiply the abundance, as a decimal, by the mass of that isotope. This is that isotope’s contribution to the atomic mass:

For chlorine-35: 0.7577 x 35.00 amu = 26.52 amu For chlorine-37 0.2423 x 37.00 amu = 8.965 amu

Sum these partial weights to get the weighted average atomic mass of chlorine:

26.52 amu + 8.965 amu = 35.49 amu

Step 3

Atomic Mass Determination

Nitrogen consists of two naturally occurring isotopes 99.63% nitrogen-14 with a mass of

14.003 amu 0.37% nitrogen-15 with a mass of

15.000 amu What is the atomic mass of

nitrogen?