Unit 2 Lesson #5Avogadro’s Number

& The Mole (p.14-16)

How Big is A Mole?

A. What is the Mole?

1. A counting number (like a dozen)

2. Avogadro’s number (NA)

1 mole = 6.022 1023 representative particles

3. Using Dimensional Analysis to Make Conversions

a. Convert 48 eggs to dozens of eggs

Conversion factor :

48 eggs X 1 dozen

1 12 eggs

b. Convert 6 dozen to number of eggs

Conversion factor :

6 dozen X 12 eggs 1 1 dozen

4. Molar Conversion Factors

a. # of Particles (atoms, molecules, ions, etc.)1 mole = 6.022 1023 particles

b. Molar mass = mass of 1 mole of a substance

1 mole = molar mass

c. Molar Volume = 22.4 Liters for any gas at STP (Standard Temperature Pressure)

*STP = T = 0o C or 273 K P = 1.0 atmosphere (atm)

1 mole = molar volume

Mole Relationships

http://itschemistrytime.blogspot.com/2011_11_01_archive.html

Representative Particles & Moles

Substance Chemical Formula

Representative Particle

Rep Particles in 1.00 mole

Carbon C 6.02 x 1023

Nitrogen gas N2

Calcium ion Ca2+

Magnesium fluoride

MgF2 6.02 x 1023

Representative Particles & Moles

Substance Chemical Formula

Representative Particle

Rep Particles in 1.00 mole

Carbon C Atom 6.02 x 1023

Nitrogen gas N2 Molecule 6.02 x 1023

Calcium ion Ca2+ Ion 6.02 x 1023

Magnesium fluoride

MgF2 Formula unit 6.02 x 1023

B. Mole to Particle Conversions

MOLESNUMBER

OF

PARTICLES

6.022 1023

NA

(particles/mol) Particles = atoms, molecules, formula

units, ions, etcNA atoms/mol

NA molecules/mol

1. How many molecules are in 2.50 moles of C12H22O11?

2.50 molC12H22O11

6.02 1023

moleculesC12H22O11

1 mol C12H22O11

= 1.51 1024

molecules C12H22O11

2. If you have 2.23 x 1018 atoms of sodium, how many moles is that?

2.23 1018

atoms Na1 mole Na

6.02 1023

atoms Na

3.70 x 10-6

moles Na=

3. How many formula units is 3.75 moles of calcium hydroxide?

3.75 mol Ca(OH)2

6.02 1023

formula unitsCa(OH)2

1 mol Ca(OH)2

= 2.26 1024

formula units Ca(OH)2

1. Molar Mass = The mass of one mole of an

element or compound

Atomic mass (on the PT) tells the... mass of each atom (amu) grams per mole (g/mol)

2. Round to 2 decimal places

C. Molar Mass Conversions

3. Molar Mass Examples

a. carbon

b. aluminum

c. zinc

12.01 g/mol

26.98 g/mol

65.39 g/mol

4. Molar Mass Examples

a. water

b. sodium chloride

H2O

2(1.01) + 16.00

NaCl 22.99 + 35.45

= 18.02 g/mol

= 58.44 g/mol

5. Molar Mass Examples

a. sodium bicarbonate

b. sucrose

NaHCO3

22.99 + 1.01 + 12.01 + 3(16.00)

= 84.01 g/mol

C12H22O11

12(12.01) + 22(1.01) + 11(16.00)

= 342.34 g/mol

6. Molar Mass Examples

a. magnesium hydroxide

b. ammonium sulfate

Mg(OH)2

24.31 + 2(16.00) + 2(1.01)

= 58.33 g/mol

(NH4)2SO4

2(14.01) + 8(1.01) + 32.06 + 4(16.00) = 132.16 g/mol

D. Molar Mass Conversions

molar mass

(g/mol)

MASS

IN

GRAMS

MOLESNUMBER

OF

PARTICLES

6.02 1023

NA

(particles/mol)

Particles = atoms, molecules, formula

units, ions, etcNA atoms/mol

NA molecules/mol

1. How many moles of carbon atoms are in 26 g of carbon?

26 g C 1 mol C

12.01 g C= 2.2 mol C

2. Find the mass of 2.1 1024 molecules of NaHCO3.

2.1 1024

MoleculesNaHCO3

1 mol NaHCO3

6.02 1023

Molecules NaHCO3

= 290 g NaHCO3

84.01 g NaHCO3

1 mol NaHCO3

1 mol K

39.10 g K

3. How many atoms are in 22.5 grams of potassium?

6.02 1023

atoms K

1 mol K

= 3.46 x 1023 atoms K

22.5 g K

E. Molar Volume Conversions

Molar Mass

Molar Vol

NA

* Molar Volume = 22.4 Liters for any gas at STP

1. What is the volume at STP of 4.00 g of CH4?

4.0g X 1 mole X 22.4 L = 5.6 L 1 16 g 1 mole

2. How many grams of He are present in 8.00 L of He at STP?

8.0 L X 1 mole X 4.0 grams = 1.4 g 1 22.4 L 1 mole