Chapter 10.1 and 10.2

Calculating atoms

Molar Mass

• Is the same as the atomic weight on the periodic table

• Element Examples 12.01 g C = 1 mol C 1.01 g H = 1 mol H 55.85 g Fe = 1 mol Fe

Molar Mass

• To find the molar mass of a compound – Count the number of each element– Multiply that number by the Average

Atomic mass for that element – Add all the elements total masses

together

Calculate molar mass of magnesium carbonate

24.3 g + 12.0 g + 3 x (16.00 g) = 84.3 g/mole

So, 84.3 g/mole = molar mass for magnesium carbonate

ExamplesExamples Calculate the molar mass of:Na2S

N2O4

C

Ca(NO3)2

= 78.05 g/mol

= 92.02 g/mol

= 12.01 g/mol

= 164.10 g/mol

What is the mole?

Not this kind of mole!

Mole - a word used to

represent a large number

of objects.Moldy

Avogadro’s Number: the number of particles

in one mole of particles.

1 mole particles = 602,000,000,000,000,000,000,000 particles1 mole particles = 602,000,000,000,000,000,000,000 particles

1 mole particles = 6.02 X 101 mole particles = 6.02 X 102323 representative particles representative particles

**Memorize this number for the test****Memorize this number for the test**

The Mole

• 12 donuts = 1 dozen donuts12 donuts = 1 dozen donuts• 12 ears of corn = 1 dozen ears of 12 ears of corn = 1 dozen ears of

corncorn• 6.02 X 106.02 X 102323 particles = 1 mole particles = 1 mole

particles.particles.• Molar mass is the mass listed on the Molar mass is the mass listed on the

periodic table in periodic table in redred rounded to rounded to closest whole numberclosest whole number

• Molar mass = 1 mole atoms = 6.02 X Molar mass = 1 mole atoms = 6.02 X 10102323 atoms atoms

• 12 donuts = 1 dozen donuts12 donuts = 1 dozen donuts• 12 ears of corn = 1 dozen ears of 12 ears of corn = 1 dozen ears of

corncorn• 6.02 X 106.02 X 102323 particles = 1 mole particles = 1 mole

particles.particles.• Molar mass is the mass listed on the Molar mass is the mass listed on the

periodic table in periodic table in redred rounded to rounded to closest whole numberclosest whole number

• Molar mass = 1 mole atoms = 6.02 X Molar mass = 1 mole atoms = 6.02 X 10102323 atoms atoms

What are Representative Particles?What are Representative Particles? The smallest pieces of a substance:

1) molecular compound - molecule2) ionic compound - formula unit (made

of ions)3) element: is the

• Remember the 7 diatomic elements? (made of molecules)

H2N2 O2 F2Cl

2

I2Br2

atoatomm

Solving Problems in Chemistry

Required Work for Solving Problems in Chemistry

• List given• List conversions• Start with given information including

proper units• Determine the units for your answer.• Put in conversions until the last unit

is what you are solving for.

Solving Problems in Chemistry

1. How many sulfur atoms are equivalent to 3 moles of sulfur atoms?

Given: 3 moles of sulfur atoms = ? Sulfur atomsGiven: 3 moles of sulfur atoms = ? Sulfur atomsConversion: 1 mole of sulfur atoms = 6.02 X 10Conversion: 1 mole of sulfur atoms = 6.02 X 1023 23 sulfur atomssulfur atoms

1.806 x 101.806 x 1024 24 atoms Satoms S3 moles S 6.02 x 1023 atoms S

1 mole S

X = 1.806 x 101.806 x 1024 24 atoms Satoms S

1

2. How many atoms are present in 3.7 moles of

sodium?3.7 moles Na = ? atoms Na

1 mole Na = 6.02 X 1023 atoms Na

3.7 moles Na 6.02 X 1023 atoms Na 1 mole Na

X == 2.22 X 1024 atoms Na2.22 X 1024 atoms Na1

List given:List given:

List conversions:List conversions:

Set Up:Set Up:

3. How many atoms are present in 155 moles of

Arsenic?155 moles As = ? atoms As

1 mole As = 6.02 X 1023 atoms As

155 moles As 6.02 X 1023 atoms As 1 mole As

X == 9.33 X 1025 atoms As 9.33 X 1025 atoms As

1

List given:List given:

List conversions:List conversions:

Set Up:Set Up:

Atoms to Moles

1. How many moles of Xenon are equivalent to 5.66 X 1026

atoms Xe?5.66 X 1026 atoms Xe = ? moles Xe

1 mole Xe = 6.02 X 1023 atoms Xe

5.66 X 1026 atoms Xe 1 mole Xe6.02 X 1023 atoms Xe

X == 940.2 moles Xe 6.02 X 1023

5.66 X 1026 moles Xe

List given:List given:

List conversions:List conversions:

Set Up:Set Up:

2. How many moles of Silver are equivalent to 2 .888 X 1015 atoms

Ag?2.888 X 1015 atoms Ag = ? moles Ag

1 mole Ag = 6.02 X 1023 atoms Ag

2.888 X 1015 atoms Ag 1 mole Ag6.02 X 1023 atoms Ag

X == 4.8 X 10-9 moles Ag2.888 X 1015 moles Ag6.02 X 1023

List given:List given:

List conversions:List conversions:

Set Up:Set Up:

Moles To Grams

1. moles of sulfur atoms equals how many grams of sulfur?

Given: 3 moles S = ? Grams SGiven: 3 moles S = ? Grams SConversion: 1 mole S = 32 grams SConversion: 1 mole S = 32 grams S

96 grams S96 grams S3 moles S X = 96 grams S96 grams S1

32 grams S

1 mole S

2. Find the mass in grams of 8.6 moles bromine

8.6 moles Br = ? grams Br

1 mole Br = 80 grams Br

8.6 moles Br 80 grams Br 1 mole Br

X == 688 grams Br 688 grams Br

1

List given:List given:

List conversions:List conversions:

Set Up:Set Up:

3. Find the mass in grams of 7.55 moles silicon

7.55 moles Si = ? grams Si

1 mole Si = 28 grams Si

7.55 moles Si 28 grams Si 1 mole Si

X == 211.4 grams Si 211.4 grams Si

1

List given:List given:

List conversions:List conversions:

Set Up:Set Up:

Grams to Moles

1. How many moles are in 38 grams of Carbon?

38 grams C = ? moles C

1 mole C = 12 grams C

38 grams C 1 mole C 12 grams C

X == 3.17 moles C 38 moles C12

List given:List given:

List conversions:List conversions:

Set Up:Set Up:

2. How many moles are in 2 grams of Hydrogen?

2 grams H = ? moles H

1 mole H = 1 grams H

2 grams H 1 mole H 1 grams H

X == 2 moles H 2 moles H1

List given:List given:

List conversions:List conversions:

Set Up:Set Up:

Grams to Particles

Solving Problems in Chemistry

1. 57 grams sulfur is equal to how many atoms of sulfur?

Given: 57 grams S = ? atoms SGiven: 57 grams S = ? atoms SConversion: 1 mole S = 32 grams SConversion: 1 mole S = 32 grams S

1 mole S = 6.02 X 101 mole S = 6.02 X 102323 atoms S atoms S

1.07 X 101.07 X 102424 atoms S atoms S57 grams S X X = 3.43 X 103.43 X 102525 atoms S atoms S

32

6.02 X 1023 atoms S

1 mole S

1 mole S32 grams S

2. How many atoms of Sulfur are in 100 grams of

Sulfur?100 grams S = ? atoms S

1 mole S = 32 grams S1 mole S = 6.02 X 1023 atoms S

100 grams S 1 mole S 32 grams S

X == 1.88 X 1024 atoms S6.02 X 1023 atoms S 1 mole S

X 6.02 X 1025 atoms S32

List given:List given:

List conversions:List conversions:

Set Up:Set Up:

The Mole-Volume RelationshipThe Mole-Volume Relationshipgases

- hard to determine masshow many moles of gas?2 things affect gas Volume:

a) Temp & b) Pressurecompare all gases at = temp & pressure

Standard Temperature and PressureStandard Temperature and Pressure

0ºC & 1 atm pressure

- abbreviated “STP” At STP, 1 mol of anyany gas has V of 22.4 L- Called molar volume

1 mol of any gas at STP = 22.4 L

Density of a gasDensity of a gas D = m / V (density = mass/volume)

- for gas units are: g / L find density of a gas at STP if formula

known You need: 1) mass and 2) volume Assume 1 mol, so mass is molar mass

(from periodic table) At STP, V = 22.4 L

If given densityIf given density, find molar mass of gas

Assume 1 mol at STP, so V = 22.4 Lmodify: D = m/V to show:

“m” will be mass of 1 mol, given 22.4 L

m = D x V

What is molar mass of a gas with density of 1.964 g/L?

How about a density of 2.86 g/L?

= 44.0 g/mol

64.0 g/mol

Notice all conversions must go Notice all conversions must go through the MOLE!through the MOLE!

Copy this conversion Copy this conversion map into your notes!map into your notes!

That’s all Folks !