Ch. 6 Notes -- Chemical Composition

What is a mole?

Mole is a unit of quantity. Like a _____________.

1 mole = 6.02x1023 atoms or molecules = “X” grams = 22.4 L gas

Dozen

The Mole!!!• A counting unit

• Similar to a dozen, except instead of 12, it’s 602 billion trillion… (602,000,000,000,000,000,000,000)

• ___________ (in scientific notation)

• This number is named in honor of AmedeoAmedeo _________ (1776 – 1856) (1776 – 1856), who studied quantities of gases and discovered that no matter what the gas was, there were the same number of molecules present…6.02 x 1023

Avogadro

6.02 x 10 23

Just How Big is a Mole?Just How Big is a Mole?

• Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles.

• If you had Avogadro's number of un-popped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles.

• If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.

• 1 dozen cookies = ___ cookies• 1 mole of cookies = ___________ cookies

• 1 dozen cars = ___ cars• 1 mole of cars = __________ cars

• 1 dozen Al atoms = ___ Al atoms• 1 mole of Al atoms = __________ atoms

Note that the NUMBER is always the same, but the ______ is very different!

Mole is abbreviated ______ .

The MoleThe Mole12

6.02 X 1023

12

6.02 X 1023

12

6.02 X 1023

MASS

mol

The Mole and Mass• Mass in grams of 1 mole equal to __________ of the

atomic masses

Practice problem:

Calculate the mass of 1 mole of CaCl2

Ca = 1 x ________ g/mol = 40.1 g/mol

Cl = 2 x ________ g/mol = 71.0 g/mol

40.1 g/mol + 71.0 g/mol = __________ g/mol CaCl2

1 mole of CaCl2 = 111.1 g/mol

the sum

40.1

35.5

111.1

Ch. 7 Notes -- Chemical QuantitiesPractice Problems:

(1) How many atoms of hydrogen are there in each compound?

a) Ca(OH)2 ___ b) C3H8O___ c) (NH4)2HPO4 ___ d) HC2H3O2 ___

(2) Calculate the formula mass of each compound. (Add up all the atomic masses for each atom from the Periodic Table.)

a) CaCO3 b) (NH4)2SO4

c) C3H6O d) Br2

2 8 9 4

Ca = 40.1C = 12.03 O’s =3 x 16.0 = 48.0

Add them up!

100.1 g/mol

2 N’s = 2 x 14.0 = 28.08 H’s = 8 x 1.0 = 8.0S = 32.14 O’s = 4 x 16.0 = 64.0

Add them up!

132.1 g/mol

C = 3 x 12.0 = 36.0H = 6 x 1.0 = 6.0O =16.0

Add them up!

58.0 g/mol

2 Br’s = 2 x 79.9 = 159.8 g/mol

3) Convert 835 grams of SO3 to moles.

4) How many molecules of CH4 are there in 18 moles?

5) How many grams of helium are there in 5.6 x 1023 atoms of helium?

6) How many molecules are there in 3.7 grams of H2O?

80.1 g SO3

1 mole SO3835 g SO3

x = 10.4 moles of SO3

1 mole CH4

6.02 x 1023 molecules CH418 moles CH4 x =

4.0 grams He5.6 x 1023 atoms He

x 3.72 grams He

18.0 grams H2O3.7 grams H2O

x = 1.23 x 1023 molecules H2O

1.08 x 1025 molecules CH4

6.02 x 1023 atoms He=

6.02 x 1023 molecules H2O

Calculating Percent Composition by MassStep 1: Find the formula mass of the compound by adding the

individual masses of the elements together.

Step 2: Divide each of the individual masses of the elements by the formula mass of the compound.

Step 3: Convert the decimal to a % by multiplying by 100.

Practice Problems:

(1) Find the % composition of the elements in each compound.

a) Na3PO4 b) SnCl4

3 Na’s = 3 x 23.0 = 69.0

P = 31.0

4 O’s = 4 x 16.0 = 64.0+164

÷ 164

÷ 164

÷ 164

= 0.421 = 42.1%

= 0.189 = 18.9%

= 0.390 = 39.0%

Sn = 118.7

4 Cl’s = 4 x 35.5 = 142.0+

260.7

÷ 260.7

÷ 260.7

= 45.5%

= 54.5%

Elements in the Universe: % Composition by Mass

Earth’s Crust: % Composition by Mass

Entire Earth (Including Atmosphere): % Composition by Mass

Human Body: % Composition by Mass

Meet The Elements

Determining the Empirical Formula for a Compound

• The empirical formula for a compound is the simplest __________ number __________ of the atoms in the compound.

Examples: H2O is the empirical formula for water.

_______ is the empirical formula for glucose, C6H12O6.

Practice Problems: What is the empirical formula for the following compounds? a) C6H6= ________

b) C8H14O2 = ________

c) C10H14O2 = _________

d) Ca5Br10 = ________

e) N3O9 = ________

wholeratio

C1H2O1

CH

C4H7O

C5H7O

CaBr2

NO3

Determining the Molecular Formula for a Compound• The molecular formula for a compound is either the same as the

empirical formula ratio or it is a “_________ _________ of this ratio. It represents the true # of atoms in the molecule.

Examples: 1) H2O is the empirical & molecular formula for water. 2) CH2O is the empirical formula for sugar, ethanoic

acid, and methanol. The molecular formula for glucose is C6H12O6, (___times the empirical ratio!)

Practice Problems: (1) If the empirical formula for a compound is CH2, which of the following is a possible molecular formula for the compound? a) C8H16 b) C8H8 c) C4H2 d) C3H9

(2) If the empirical formula for a compound is C2H3, which of the following is a possible molecular formula for the compound? a) C2H6 b) C10H15 c) C6H12 d) C8H14

whole # multiple

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