what is a mole?

What is a

MOLE?

There are 12 items in a dozen

There are 144 items in a gross of any substance

http://www.school-clipart.com/cgi-bin/admin.pl?do=license_image&image_number=0511-0708-1513-5847

There are 6.02 x 1023 atoms or molecules in a mole of any substance

I’m going to need a bigger

shovel!

6.02 x 1023

= 602, 000,000,000,000,000,000,000

A mole of standard soft drink cans would cover the surface of the Earth

to a depth of over 200 miles.

If you had a mole of unpopped 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.

Molar mass is the weight of one mole (or 6.02 x 1023 molecules) of

any chemical compounds.

Molar Masses

Water’s molar mass is 18 grams

PVC’s molar mass is 150,000 grams

How can I find the molar mass of an element?

Use the element’s mass on the periodic table

Example: What is the molar mass of Carbon?

Carbon’s atomic mass is……12.01

Therefore, Carbon’s molar mass is…..

12.01g

Example: What is the molar mass of Magnesium?

Magnesium’s atomic mass is……24.31

Therefore, Magnesium’s molar mass is….. 24.31g

Example: What is the molar mass of Krypton?

Krypton’s atomic mass is……83.80

Therefore, Krypton’s molar mass is…..

83.80g

Practice Time!

Element Molar Mass Element Molar mass

Helium (He) Argon (Ar)

Chlorine (Cl)

Neon (Ne)

Sodium (Na) Phosphorus (P)

Now, let’s

kick it up a

notch!

To calculate the molar mass of a compounds

• First you find the molar mass of the parts of the compound and then you add.

• If there are more than one of a type of atom in the compound, you multiply the number of atoms time the molar mass of the one atom, and then add all parts together.

What’s the molar mass of a compound

like NaCl?Molar mass of Na = 22.99

Molar mass of Cl = 35.45

So, the Molar mass of NaCl =

22.99+35.45

58.44g

What’s the molar mass of C6H12O6?

6 x 12.01 = 72.06

12 x 1.008 = 12.096

=180.156 g

Molar mass of C6=

Molar mass of H12= 6 x 16.00= 96Molar mass of O6=

So, the Molar mass of C6H12O6 =

Practice Time!

Compound Molar Mass Compound Molar mass

Carbon dioxide (CO2)

Ammonia (NH3)

Ethanol (C2H6O)

Sulfuric acid (H2SO4)

Challenge! Calculate the Molar Mass:

1. Ca(NO3)2

2. Ca3(PO4)2

3. (NH4)2SO4

Percent Composition

A percent is a ratio.

Sometimes we want to know how much of an element is in the compound.

Steps to determine percent composition

1. Calculate the molar mass from the formula.

2. Determine how many grams the atom of interest contributes to the compound

3. Divide the mass of the atom by the molar mass and multiply by 100 to get a percentage.

% Composition = Mass of the element in cmpd x 100 Molar Mass of cmpd

Example: Find the % of Na and Cl in NaCl

Sodium Chloride, NaClNa = 22.99g Cl = 35.45g Molar Mass = 58.44g

%Na = 22.99 x 100 58.44 =39.34 % Na

%Cl = 35.45 x 100 58.44 = 60.7% Cl

Find the % of each element in Na2SO4

Give the % composition of all the elements in

Magnesium sulfiteFormula

Relating Moles & Mass

What you already know….How big is a mole? 6.02 x 1023 atoms or molecules

How do you determine molar mass of an atom?

It’s the same as atomic mass.

How do you determine molar mass of a molecule?

It’s the same as the sum of the atomic masses of the parts.

Chemist use moles to understand relationships between reactants and products. In the lab we don’t have a balance that measures moles. We must relate grams to the number of moles.

What you don’t know

• How many moles are in this glass of water?

What else you don’t know

• Can you add 3.25 moles of water to the beaker?

These two questions can be solved by

using

conveRsins!

A Conversion is just a math equation in which you START with the data and units they give you in the problem, and then MULTIPLY by CONVERSION FACTORS until you have the right units at the end.

What’s a Conversion Factor?It’s a FRACTION in which the TOP

number and BOTTOM number mean the same thing but have different units.

12 eggs1 dozen

1 week7 days

3 feet1 yard

6 points1 touchdown

100 yards1 football field

1 cup8 ounces

Write 3 of your own!

Mole Conversion

Molar Mass or 1 Mole1 Mole Molar Mass

How do you know which part to put on top and which part to put on

bottom?Because 12 eggs

1 dozen Is the same thing as 1 dozen12 eggs

How do you know which one to use?

RULE!!!!Use the conversion factor with the UNITS of the info they give you in the problem on the BOTTOM and

the UNITS of what you’re LOOKING FOR on the TOP!!

Steps to conversions

1. Write the given.2. Draw a “times and a line”3. Write the units you were given on the bottom4. Write the units you want on top5. Fill in the conversion factor (remember 1 is

always with the mole)6. Multiply all the numbers on the top and divide it

by the numbers on the bottom.

So, if they tell you there are 8 dozen and ask you how many eggs there are:

START with what they give you

8 dozen

MULTIPLY

X

By a conversion factor that connects eggs to dozens. How many eggs in ONE dozen?

12 eggs1 dozen

NOTE: The “dozen” in the first number and the “dozen” in the bottom of the conversion factor will cancel each other out, leaving eggs!!!

= 96 eggs

For example:How many grams are in 3 moles of

Carbon?


3 moles

MULTIPLY

X

By a conversion factor that connects moles to grams. How many grams in ONE mole of hydrogen?

12.00 grams 1 mole C

NOTE: The moles in the first number and the moles in the bottom of the conversion factor will cancel each other out, leaving grams!!!

=36.00 g

Another example, this time a little trickier:How many grams are in 5 moles of

carbon dioxide (CO2)?


5 moles CO2

MULTIPLY

X

By a conversion factor that connects moles to grams. How many grams in ONE mole of carbon dioxide?

44.01 grams 1 mole CO2

NOTE: The moles in the first number and the moles in the bottom of the conversion factor will cancel each other out, leaving grams!!!

= 220.05 g

Practice Time!

• How many grams are there in 350 moles of iron (Fe)?

• How many grams are there in 3 moles of Lithium (Li)?

• How many grams are there in 46 moles of water (H2O)?

• How many grams are there in 12.7 moles of magnesium chloride (MgCl2)?

• A chemist needs 12.5 moles of sulfuric acid (H2SO4). How many grams does he need?

We could, on the other hand, give you GRAMS and ask you to find MOLES. That would be a

GRAMS TO MOLES problem.

Those problems you just finished were all “MOLES TO GRAMS ” problems because they

GAVE you moles and asked you to find grams.

For example:How many moles are in 250 grams of

Carbon?


250 grams

MULTIPLY

X

By a conversion factor that connects moles to grams. How many grams in ONE mole of carbon?

1 mole C 12.00 grams

NOTE: The grams in the first number and the grams in the bottom of the conversion factor will cancel each other out, leaving moles!!!

= 20.83 moles

Another example, this time a little trickier:How many moles are in 930 grams of

carbon dioxide (CO2)?


930 grams

MULTIPLY

X

By a conversion factor that connects moles to grams. How many grams in ONE mole of carbon dioxide?

1 mole CO2

44.01 gramsNOTE: The grams in the first number and the grams in the bottom of the conversion factor will cancel each other out, leaving moles!!!

= 21.13 moles

Practice Time!

• How many moles are in 2.4 grams of sulfur (S)?

• How many moles are in 18.7 grams of argon (Ar)?

• How many moles are in 88.1 grams of potassium chloride (KCl)?

• How many moles are in 2.3 grams of nitric acid (HNO3)?

• How many moles are in 11.9 grams of calcium hydroxide - Ca(OH)2? (Don’t forget! The 2 subscript applies to the O and to the H!!)

• How many moles are in 2.4 grams of sulfur (S)? 0. 0748 mol S

• How many moles are in 18.7 grams of argon (Ar)? 0.468 mol Ar

• How many moles are in 88.1 grams of potassium chloride (KCl)? 1.18 mol

• How many moles are in 2.3 grams of nitric acid (HNO3)? 0.036 mol

• How many moles are in 11.9 grams of calcium hydroxide - Ca(OH)2? (Don’t forget! The 2 subscript applies to the O and to the H!!) 0.16 mol

Stoichiometry

• The study of quantitative relationships between reactants and products

• Balanced chemical equations relate moles of reactants to moles of product

N2 + 3H2 2NH3

• The coefficients are the mole ratio • 1 mole of N2 and 3 moles of H2 make 2 moles

of NH3

Sample Problems

2 KClO3 2KCl + 3O2

2 moles of KClO3 can produce __ moles of KCl.

4 moles of KClO3 can produce __ moles of KCl.

Theoretical Yield

• Yield = the amount of product• Goal – make as much of the product as

possible• Theoretical Yield – the most you should make

as predicted by the chemical reaction using stoichiometry: N2 + 3H2 2NH3

Actual Yield

• the amount of product actually produced in the lab

• Usually lower due to collection techniques and apparatus used

• If the amount is higher than predicted then there may be impurities in the product

Percent Yield

• Measures how well you did the lab

Percent yield = Actual yield x 100 theoretical yield

Limiting Reactant• Sometimes, when two or more reactants are

present in a reaction, more than the other is available for reacting.

• The one thing that there is not enough of is called the limiting reactant.

• It is the reactant that is used up first.

Unit 5 Notes - Winter 2014 57

Limiting Reactant Example #1:Making a Bicycle

Making a bicycle requires1 frame + 2 wheels 1 bicycle

a)If you have 100 frames and 120 wheels, howmany bicycles can you manufacture? ______a)What is the limiting reactant? _________


Limiting Reactant Example #2:Grilled Cheese Sandwich

Bread + Cheese ‘Cheese Melt’

2 B + C B2C

100 bread 30 slices ? sandwiches


Limiting Reactant Example #3:Chemistry Problem

Hydrogen gas can be produced by the reaction of magnesium and hydrochloric acid, as shown by this equation:

Mg(s) + 2HCl (aq) MgCl2(aq) + H2(g)In particular, 6,000 molecules of HCl were mixed with 1,000

molecules of Mg.

a)Which reactant is limiting? ________________________

b) How many molecules of H2 are formed when the reaction is complete? ______________________________________


what is a mole?

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