Bell Ringer

What is a Mole?

What is the mass of a NaCl molecule?

Chapter 7.1b

Common counting units: shoes by the pair (pair = 2)eggs by the dozen (dozen = 12)paper by the ream (ream = 500 sheets).

Counting With Moleso Chemical reactions usually involve very large

numbers of tiny particleso We use a counting unit called the mole to

measure amounts of a substance.

o Mole (mol) = amount of any substance that contains approximately 6.02 × 1023 particles.o This amount is known as Avogadro’s

number.o Ex: 1 mole of iron = 6.02 × 1023 atoms of

iron.

Molar Mass:mass of one mole of a substance same as atomic mass, in grams.

Examples: Carbon:

Atomic mass = 12.0 amuMolar mass = 12.0 grams.

Sulfur: Atomic mass = 32.1 amuMolar mass = 32.1 grams.

o Molar Mass of a compound = o sum of atomic masses of all its atoms,

expressed in grams.o Tells us the total grams in one mole of the

compound

Example: Carbon dioxide (CO2)

• 1 carbon atom = 12.0 amu• 2 oxygen atoms = (2 × 16.0 amu) = 32.0 amu

• CO2 atomic mass = (12.0 + 32.0) = 44.0 amu

• CO2 molar mass = 44.0 grams

• 44.0g CO2 in 1 mol CO2

Counting With Moles

Mole-Mass ConversionsKnowing the molar mass of a substance lets you easily convert between moles and mass

“converting” means you can calculate one from the other

Example:Molar mass of CO2 is 44.0 grams

1.0 mole of CO2 = 44.0 grams

Conversion factors

OR

Recipe calls for 4 eggs per cake and you plan to make 3 cakes. Eggs can only be bought by the dozen (i.e. groups of 12). How may dozen eggs do you need to buy?

Conversion factors: 4 eggs 1 cake 1 cake 4 eggs

12 eggs 1 doz. eggs 1 doz. eggs 12 eggs

Calc: 3 cakes x 4 eggs x 1 doz eggs = 1 doz eggs

1 cake 12 eggs

Converting Example: Chocolate Cake Recipe

o You have 55.0 grams of CO2. How many

moles?o To calculate how many moles of CO2 you

have, multiply the mass by a conversion factor.

o You can check your answer.

Counting With Moles

Chemical Calculations

o In chemical reactions, the mass of a reactant or product can be calculated.o Use a balanced chemical equation

and the molar masses of the reactants and products.

o In a balanced chemical equation, the number of atoms of each element on the left equals the number of atoms of each element on the right.

Chemical Calculations

o The Coefficient tells us the # of moles of each reactant and product involved the reaction

Chemical Calculations

Chemical Calculations

o Molar Mass = the # of grams per mole of each reactant and product

Chemical Calculations

o Mass (of a reactant or product) = o the # of moles in the balanced equation

(Coefficient) x the molar mass.

Converting Mass to Moles

To calculate how much oxygen is required to make 144 grams of water, begin with a balanced chemical equation for the reaction.

2H2 + O2 2H2O

• Determine how many moles of water you are trying to make. • Convert the given mass (144g) of water into moles.

Chemical Calculations - Stoichiometry

Using Mole Ratios Write the conversion factors, or mole ratios.

2H2 + O2 2H2O

Calculate how many moles of oxygen are required to produce eight moles of water.

Chemical Calculations

Converting Moles to Mass Convert moles of O2 to grams of O2 by

using the molar mass of O2 as a conversion factor.

To produce 144 grams of H2O, you must supply 128 grams of O2.

Chemical Calculations

Assessment Questions

1. Which of the following is a balanced chemical equation for the reaction of aluminum and ammonium perchlorate? a. Al + NH4ClO4 —› Al2O3 + NH4Cl

b. 4Al + 3NH4ClO4 —› 4Al2O3 + 3NH4Cl

c. 8Al + NH4ClO4 —› 4Al2O3 + NH4Cl

d. 8Al + 3NH4ClO4 —› 4Al2O3 + 3NH4Cl

Assessment Questions

1. Which of the following is a balanced chemical equation for the reaction of aluminum and ammonium perchlorate? a. Al + NH4ClO4 —› Al2O3 + NH4Cl

b. 4Al + 3NH4ClO4 —› 4Al2O3 + 3NH4Cl

c. 8Al + NH4ClO4 —› 4Al2O3 + NH4Cl

d. 8Al + 3NH4ClO4 —› 4Al2O3 + 3NH4Cl

ANS: D

Assessment Questions

2. How many moles of NaCl (molar mass = 58.5) are there in a 5.85-gram sample?a. 58.5 molb. 5.85 molc. 0.10 mold. 0.28 mol

Assessment Questions

2. How many moles of NaCl (molar mass = 58.5) are there in a 5.85-gram sample?a. 58.5 molb. 5.85 molc. 0.10 mold. 0.28 mol

ANS: C

Assessment Questions3. In the reaction shown below, how many

grams of hydrogen are produced when 10 moles of potassium react with water?2K + 2H2O —› 2KOH + H2

a. 2.5 g

b. 5 g

c. 10 gd. 20 g

Assessment Questions3. In the reaction shown below, how many

grams of hydrogen are produced when 10 moles of potassium react with water?2K + 2H2O —› 2KOH + H2

a. 2.5 g

b. 5 g

c. 10 g

d. 20 g

ANS: C

Assessment Questions

1. In the chemical equation below, the reactants are carbon dioxide and water.

CH4 + 2O2 —› CO2 +2H2O

True <or> False?

ANS: False, products