“THE MOLE”

Counting Quantities1.) You can count how many of something you

have……12 doughnuts in a dozen

10 pins knocked down for a strike

2.) You can measure the mass of what you have…….

buying candy by the poundgold is priced by the gram

3.) You can measure matter by volume…..gasoline by the liter

medicine in mL

“THE MOLE”

(Molar Mass = 1 MOLE)

A convenient standard quantity of a substance

For solids, liquids, gases…..you can convert weight to moles, or moles to weight

The amount of a substance = in grams to the sum of the atomic weights

1 mole =6.02 x 1023 particles• What do I mean when I say particles?

–Can be atoms, molecules, formula units, or ions.

ELEMENT use atoms

COVALENT COMPOUND use molecules

IONIC COMPOUND use formula units

ION use ions

Examples• Na

– I mole of Na = 6.02 x 1023 atoms of Na

• H2O

– 1 mole of H2O = 6.02 x 1023 molecules of H2O

• NaCl– 1 mole of NaCl = 6.02 x 1023 formula units of NaCl

• Cl-– 1 mole of Cl- = 6.02 x 1023 ions of Cl-

MOLAR MASS AND NUMBER OF PARTICLES

Substance Molar Mass Number of Particles in One Mole• Carbon (C) 12.0 g 6.02 x 1023 C atoms

• Sodium (Na) 23.0 g 6.02 x 1023 Na atoms

• CaCO3 (antacid) 100.1 g 6.02 x 1023 CaCO3 formula units

• C6H12O6 (glucose) 180.0 g 6.02 x 1023 glucose molecules

• C8H10N4O2 (caffeine) 194.0 g 6.02 x 1023 caffeine molecules

Example problems

• How many moles is 3.46 x 1026 molecules of water?

• How many moles of hydrogen are in 3.46 x 1026 molecules of water?

• How many atoms is 3.46 moles of silver?

A dozen…• Will a dozen trucks have the

same mass as a dozen chocolates?

• Will 6.02 x 1023 molecules of water have the same mass as 6.02 x 1023 molecules of CO2?

Atomic Mass Unit (AMU)

• AMU = mass of a single atom

• AMU are relative values based on the mass of the most common isotope of carbon.

Molar Mass

• More convenient to use

UNITS: g/mol• MM= mass of one mole of a substance

….remember???

Molar MassUse periodic table to find MM of a

compound:

1. Multiply each element’s mass (from the periodic

table) by number of atoms present

2. Add all the masses together

Practice Problem

• Find the molar mass of (NH4)2O

Did you get 52 g/mol?

• How many grams is 2.35 moles of MgO?

Practice Problem

• How does the amount of moles of 44 g of CO2 compare to 36.6 g of HCl?

–Same amount of moles; therefore, same amount of molecules (6.02 x 1023)

Example

• How many moles is 300 g CO2?

• 1. Determine the relationship between g CO2 and moles of CO2 (find molar mass)

• 2. Cancel out units and solve.

Solution44 g CO2 = 1 mole CO2

300 g CO2

44 g CO2

1 mole CO2

= 6.82 mole CO= 6.82 mole CO22

Example

• How many molecules is 6.82 moles CO2?

• Determine the relationship between moles of CO2 and molecules CO2

(Avogadro’s number)

• 2. Cancel out units and solve.

Solution

6.82 mole CO2

1 mole CO2

6.02 x 1023 molecules

= 4.11 x 10= 4.11 x 102424 molecules COmolecules CO22

• NOTICE: to get from grams to molecules you have to go through the MOLE– Remember in chemistry all roads lead

to the mole!

MOLAR VOLUME

• PV=nRT

– What is the volume of 1 mole of gas of oxygen at STP?

– What is the volume of 1 mole of gas of hydrogen at STP?

MOLAR VOLUME

• Gases can change volume based on temperature and pressure

• BUT at STP 6.02 x 1023 molecules (1 mole) = 22.4 L

– This is true of ANY gas!– How many liters are in 12.3 moles of H2SO4

(gas) at STP?

12.3 moles H2SO4

1 mole H2SO4

22.4 Liters

= 276 liters H= 276 liters H22SOSO44

Mole Road Map

Example

• What volume is occupied by 90 g CO2 at STP?

• 1. Determine conversion factors

• 2. Use factor label

1 mole CO2 = 44 g CO2

1 mole CO2 (at STP) = 22.4 L CO2

90 g CO21 mole CO2

44 g CO2

22. 4 L CO2

1 mole CO2

= 45.8 L CO2

HAPPY VALENTINE’S DAY• Make a poem!!!

ROSES ARE RED

VIOLETS ARE BLUE

MOLAR MASS SURE IS SWEET

AND MOLAR VOLUME IS TOO

MOLE MOVIE

• http://www.learner.org/resources/series61.html#

BELLWORK 2-16

• Convert 3.49 x 1029 ions of PbCl2 to moles.

• What is the mass of hydrogen in 50.0 grams of C3H8?

PERCENT COMPOSITION

• Relative amounts of elements in a compound are expressed as PERCENT COMPOSITION.

                                                                                 

                                                                                                   

% composition steps

• Step 1: Find the total mass of the compound

• Step 2: Divide the total mass of each element by the total mass of the compound

• Step 3: Multiply by 100

Example

• K2CrO4

• Total mass = 2 K (39.1 x 2) + Cr (52)

+ 4 O (16 x 4) 194.2 g

• K: 78.2 g/ 194.2 g = .403 x 100 = 40.3% K

• Cr: 52 g/ 194.2 g = .268 x 100 = 26.8 % Cr

• O: 64 g/ 194.2 g = .329 x 100 = 32.9 % O

32.9 % + 26.8 % + 40.3% = 100%

CAFFEINE: C8H10N4O2

ELEMENTPERCENT

COMPOSITION

Carbon  12(8)= 96 grams    

96/194= .4948 x10049.5%

Hydrogen  1(10)= 10 grams     10/194= .052 x100

5.2%

Nitrogen   14(4)= 56 grams     56/194= .289 x100

28.9%

Oxygen      16(2)= 32 grams     32/194= .165 x100

16.5%

EMPIRICAL FORMULAS

• The lowest whole-number ratio of the atoms of the elements in a compound

• Is C2O4 an empirical formula?

• CO2

1:2 ratio between Carbon and Oxygen

• Is H2SO4 an empirical formula?

– Yes, because you can’t reduce the subscripts any further. (2:1: 4 ratio)

• A compound is analyzed and found to contain 25.9% nitrogen and 74.1% oxygen. What is the empirical formula of the compound?

STEPS FOR EMPIRICAL FORMULA PROBLEMS

• sTeP 1: change all percents of elements to grams

• sTeP 2: divide grams of each element by molar mass of each element- this will give you moles of each element

• sTep 3: divide moles of each element by the smallest amount of moles

• sTeP 4: if the ratios are not in whole numbers multiply each by the smallest whole number that will convert both subscripts to whole numbers

Example Problem

• Step 1: 25.9 grams of Nitrogen74.1 grams of Oxygen

• Step 2: 25.9 g x 1 mol = 1.85 mol N 14 g

74.1 g x 1mol = 4.63 mol O 16 g

• Step 3: 1.85 mol N/ 1.85 = 1 mol N 4.63 mol O/ 1.85 = 2.5 mol O

• Step 4: multiply mol N and mol O by 2 to get whole numbers: 2 mol N and 5 mol O

• Empirical formula equals N2O5

Class work

• What is the empirical formula of a compound that is 52.5% Phosphorus and 47.5% Oxygen?

• What is the empirical formula of a compound that is 10.0% C, .80% H, and 89.1% Cl?

• What is the empirical formula of a compound that is 7.8% C and 92.2% Cl?

Did you get these answers?

• P4O7

• CHCl3• CCl4

Bellwork 2/20

• #1: Which of the following can be classified as an empirical formula?

a) SCl2 b) C6H10O4 c) Na2SO3

• #2: What is the empirical formula of a compound that is 60.0 % Magnesium and 40.0% oxygen?

SOLUTION

• #1: a and c are empirical formulas

• #2: Change % to grams

• 60.0% Magnesium= 60.0 g Magnesium

• 40.0 % Oxygen = 40.0 g Oxygen

• 2. Convert the grams of each element to moles (using the molar mass)

60.0 g Magnesium 1 mole Magnesium

24.3 g Magnesium

= 2.46 moles Magnesium

Solution Continued

• Oxygen:

40.0 g Oxygen 1 mole Oxygen

16.0 g Oxygen

= 2.50 moles Oxygen

Solution Continued

• 3. Now divide the number of moles for each element by the smallest number of moles.

• 2.46 moles Magnesium• 2.50 moles Oxygen• Magnesium has the smallest number of

moles {2.46 moles}• So divide the number of moles of

Magnesium and Oxygen by 2.46

Solution Continued

• Magnesium = 2.46 moles / 2.46 moles = 1 Mg

• Oxygen = 2.50 moles / 2.46 moles= 1.02 O

• Mg1O1

•MgO is the empirical formula

MOLECULAR FORMULAS

• Is a simple whole-number multiple of the empirical formula– Can be the same as its experimentally

determined empirical formula.

– EXAMPLE: C8H16 is the molecular formula

CH2 would be the empirical formula

STEPS FOR FINDING MOLECULAR FORMULA

• Step 1: First find the empirical formula following the steps given previously (sometimes it may be given to you)

• Step 2: Divide molar mass of compound by empirical formula mass.

• Step 3: Multiply each subscript in the empirical formula by the value you got in step 2.

• The molar mass of a a compound is 90 g/mol. The empirical formula is CH2O. What is the molecular formula?

• Solution: 90/30= 3– Therefore, molecular formula = C3H6O3

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                                                                                                    Slide 12 of 26

• What is the molecular formula of the compound if the empirical formula is CO2 and the molecular mass is 132 g?

• Nicotine, a component of tobacco, has an empirical formula of C5H7N. The molar mass of nicotine is 162 g. What is its molecular formula?

• A compound contain 64.9% C, 13.5% H, and 21.6% O. Its molecular mass is 74 g. Find the molecular formula.

• What is the molecular formula of a compound with an empirical formula of CH4N and molecular mass of 60?

• The molar mass of CH4N is 30 g.• The molecular mass is 60 g.• Thus, molecular mass of CH4N / empirical

gfm• 60 g / 30 g • = 2

• You need to multiply each atom in the empirical by a factor “2”

• Thus CH4N becomes C2H8N2

• C2H8N2 is the molecular formula

HYDRATES

• Hydrates are compounds that contain weakly bound water molecules as part of its crystal structure. – Appear dry

• The water is not actually part of the chemical substance and this is reflected in the way the formula is written. – BaCl2 . 2 H2O

The Nomeclature of Hydrates

• Example: CuSO4 . 5 H2O

– copper(II) sulfate pentahydrate

Try These

• Na2SO4 .10H2O

– Sodium sulfate decahydrate

• Calcium chloride dihydrate– CaCl2 . 2H2O

Finding the Empirical Formula Hydrate Style

• Example #1: A hydrate of magnesium iodide has a formula MgI2. X H2O. A 1.055 g sample is heated to a constant value of 0.695 g. What is the value of X?

• Step 1: Determine from problem the grams of H2O and grams of compound (MgI2)– MgI2 = .695 g– H2O = .36 g

SOLUTION

• Step 2: Calculate the number of moles of MgI2 in the final sample: – Moles MgI2 = .695 g/ (278.1 g/mol) = .0025

moles

• Calculate the number of moles of H2O in the sample using the molar mass of H2O = 18.02, and the mass of the evaporated H2O = 0.36 g. – Moles H2O = .36 g/ (18.02 g/mol) = .020

moles

•

• Step 3: Divide by the lowest number of moles (will always be moles of compound, not water) .02/.0025 = 8

.0025/.0025 = 1

And the molecular formula is:

MgI2 . 8 H2O

Hydrate Problems

• Practice Problems

Application of Hydrates?• Methane Hydrate could potentially be a

new energy source. If only one percent of the methane hydrate resource could be made technically and economically recoverable, the United States could more than double its domestic natural gas resource.

Global Climate Hazard

• If global warming occurs, the temperature will rise and decompose some of these methane hydrates in the earth.  Methane is one of the most harmful greenhouse gases and this effect could be potentially threatening.

Electronic Equipment?

• Cameras made in Japan are often shipped to America by ships

• A calcium chloride hydrate is often packaged with the camera in the box to absorb moisture so the camera won’t be damaged.

Bellwork 2/22

• You have a 35.64 g sample of hydrated barium bromide.  The sample is heated to drive off the water. The dry sample has a mass of 30.42 g of barium bromide.  What is the formula for the hydrate?

ANSWER TO BELLWORK 2/22

• BaBr2 * 3H2O

Warm-Up 10-23

• Propane is a gas used for cooking and heating. How many atoms are in 2.12 moles of propane? (Propane = C3H8)

• What is the percent composition of C and H in propane? – 1.40 x 1025 atoms

Warm-Up 10-24

• Calculate the mass of 7.89 x 1020 atoms of iron (Fe).

Warm-Up 10-25-06

• What is the molar mass of NaHCO3?

• How many moles is .346 grams of H2SO4?

• 12.89 moles of Potassium Chloride equals how many formula units of Potassium Chloride?