The MoleChapter 10

What is a Mole?

•A unit that is a specified number of particles (atom, molecule, ion, or formula unit)

•Avogadro’s Number: 6.02 x 1023 representative particles.

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 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.

• 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.

Three types of conversions with the Mole

1.Mole Representative Particles2.Mole Mass3.Mole Volume at STP

This is your task and you have to do it…You must find in your textbook the three conversion factors we are going to be using to convert back and forth.

The Mole• 1 dozen cookies = 12 cookies• 1 mole of cookies = 6.02 X 1023 cookies

• 1 dozen cars = 12 cars• 1 mole of cars = 6.02 X 1023 cars

• 1 dozen Al atoms = 12 Al atoms• 1 mole of Al atoms = 6.02 X 1023 atoms

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

= 6.02 x 1023 C atoms

= 6.02 x 1023 H2O molecules

= 6.02 x 1023 NaCl “molecules”(technically, ionics are compounds not

molecules so they are called formula units)

6.02 x 1023 Na+ ions and

6.02 x 1023 Cl– ions

A Mole of Particles Contains 6.02 x 1023 particles

1 mole C

1 mole H2O

1 mole NaCl

6.02 x 1023 particles

1 mole

or

1 mole

6.02 x 1023 particles

Note that a particle could be an atom OR a molecule!

Avogadro’s Number as Conversion Factor

Example 1- Number of Particles and Moles

How many moles of magnesium is 1.25 x 1023 atoms of magnesium?

Example 2- Number of Particles and Moles

How many moles is 2.80 x 1023 atoms of silicon?

Converting Moles to Molar Mass

• To convert from moles to mass or mass to moles you must find molar mass (mass of a mole)

• Units used for molar mass: atomic mass units (amu)• The molar mass of an element is found on the periodic table• The molar mass of a compound you must solve (hahaha and if your

writing this, sucka’)

1 mole of CaCl2 = ?

1 mole Ca x 40.1 g/mol

+ 2 moles Cl x 35.5 g/mol

= 111.1 g/mol CaCl2

Molar Mass of Molecules and Compounds

Prozac, C17H18F3NO, is a widely used

antidepressant that inhibits the uptake of

serotonin by the brain. Find its molar mass.

Example- Molar Mass

molar mass

Grams Moles

Calculations with Molar Mass

Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al?

3.00 moles Al ? g Al

Converting Moles and Grams

1. Molar mass of Al 1 mole Al = 27.0 g Al

2. Conversion factors for Al

27.0g Al or 1 mol Al

1 mol Al 27.0 g Al

3. Setup 3.00 moles Al x 27.0 g Al

1 mole Al

Answer = 81.0 g Al

The artificial sweetener aspartame

(Nutra-Sweet) formula C14H18N2O5 is

used to sweeten diet foods, coffee and

soft drinks. How many moles of

aspartame are present in 225 g of

aspartame?

Example- Moles to Mass

Mole-Volume Relationship

• Volume of gas varies with changes in temperature and changes in pressure.

• Due to these variations, the volume of a gas is measure at Standard Temperature and pressure (STP).

• Temperature 0˚C

• Pressure 101.3 kPa or 1 atmosphere (atm)

Conversion Factor

 

Example

Sulfur dioxide is a gas produced by burning coal. Determine the volume, in liters of 0.60 mole SO2 gas at STP.

Example

At STP, what volume is occupied by each of the following gases?

1. 6.7 mol H2

2. 2.56 mol CH4

Atoms/Molecules and Grams

• Since 6.02 X 1023 particles = 1 mole AND

1 mole = molar mass (grams)• You can convert atoms/molecules to moles

and then moles to grams! (Two step process)

• You can’t go directly from atoms to grams!!!! You MUST go thru MOLES.

• That’s like asking 2 dozen cookies weigh how many ounces if 1 cookie weighs 4 oz? You have to convert to dozen first!

molar mass Avogadro’s number Grams Moles particles

Everything must go through Moles!!!

Calculations

Atoms/Molecules and Grams

How many atoms of Cu are present in 35.4 g of Cu?

35.4 g Cu 1 mol Cu 6.02 X 1023 atoms Cu 63.5 g Cu 1 mol Cu

= 3.4 X 1023 atoms Cu

Learning Check!

How many atoms of K are present in 78.4 g of K?

Learning Check!

What is the mass (in grams) of 1.20 X 1024 molecules of glucose (C6H12O6)?

Learning Check!

How many atoms of O are present in 78.1 g of oxygen?

78.1 g O2 1 mol O2 6.02 X 1023 molecules O2 2 atoms O 32.0 g O2 1 mol O2 1 molecule O2

Stoichiometry!!!

•The calculation of quantities in chemical reactions

•We will use balanced chemical equations to calculate how much reactant is needed or how much product is produced in a reaction.

Writing and Using Molar Ratios

•Use molar ratios as a new conversion factor to convert between a given number of moles of a reactant or product to moles of a different reactant or product.

• It is made from the coefficients of a balanced chemical equation interpreted in terms of moles.

Example 1

How many grams of NH3 are produced when 0.60 moles of nitrogen reacts with hydrogen?

N2 + H2 NH3

Example 2

How many atoms of aluminum are needed to form 3.7 moles Al2O3?

Al + O2 Al2O3

Example 3

What volume (L) of oxygen are required to react completely with 14.8 moles Al?

4Al + 3O2 2Al2O3

Example 4

How many grams of Al2O3 are formed when 0.78 mol O2 reacts with aluminum?

4Al + 3O2 2Al2O3

Example 5

Iron (III) oxide reacts with carbon monoxide to yield iron and carbon dioxide in the following reaction:

Fe2O3 + 3CO 2Fe + 3CO2

How many atoms of Fe are produced from 1.8 mol of Fe2O3?

Limiting/ Excess Reagent

•In a chemical reaction, the reactant that determines the amount of product that can be formed by a reaction is the limiting reagent.

•The reactant that is not completely used up in a reaction is called the excess reagent.

How to find limiting Reagent

Approach 2: Find the limiting reagent by calculating and comparing the amount of product each reactant will produce.1. Balance the chemical equation 2. Convert the given information into moles (if necessary).3. Use stoichiometry for each individual reactant to find the mass of product

produced.4. The reactant that produces a lesser amount of product is the limiting

reagent.5. The reactant that produces a larger amount of product is the excess reagent.6. To find the amount of remaining excess reactant, subtract the mass of excess

reagent consumed from the total mass of excess reagent given.

Example 1

Consider respiration, one of the most common chemical reactions on earth.

C6H12O6+6O2→6CO2+6H2O+energy

What is the limiting reagent in the reaction of 25 grams of glucose with 40 grams of oxygen?

Example 2What is the limiting reagent if 2.40 g Mg reacts with 10.0 g O2?

Mg+O2→MgO

Example 3

What is the limiting reagent if 76.4 grams of C2H3Br3 were reacted with

49.1 grams of O2?

4C2H3Br3+11O2→8CO2+6H2O+6Br2

Example 4

How much the excess reagent remains if 24.5 grams of CoO is reacted with 2.58 grams of O2?

4CoO+O2→2Co2O3

Percent Yield

• The ratio of the actual yield to the theoretical yield expressed as a percent.

• Actual yield- the amount of product that actually forms when the reaction is carried out in the lab.

• Theoretical yield- the maximum amount of product that could be formed from given amounts of reactants.

Percent Yield = x 100

Example 1

What is the percent yield if 13.1 grams CaO is actually produced when 24.8 g CaCO3 is heated?

CaCO3 CaO + CO2