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 Moles

o o Chemical reactions usually involve very large numbers of tiny particles 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 × 10 23 particles.

o This amount is known as

Avogadro’s number

.

o Ex: 1 mole of iron = 6.02 × 10 23 iron.

atoms of

Molar Mass:

 mass of one mole of a substance  same as atomic mass, in grams. Examples:  Carbon:  Atomic mass = 12.0 amu  Molar mass = 12.0 grams.  Sulfur:  Atomic mass = 32.1 amu  Molar mass = 32.1 grams.

Counting With Moles

o Molar Mass of a compound = o o

sum

of atomic masses of all its atoms, expressed in grams.

Tells us the total grams in one mole of the compound • • • • Example: Carbon dioxide (CO 2 ) 1 carbon atom = 12.0 amu 2 oxygen atoms = (2 × 16.0 amu) = 32.0 amu • CO 2 CO 2

atomic mass molar mass

= 44.0

grams

44.0g CO 2 = (12.0 + 32.0) = 44.0 in 1 mol CO 2 amu

Mole-Mass Conversions

  Knowing 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 CO 2 is 44.0 grams 1.0 mole of CO 2 = 44.0 grams  Conversion factors  OR

Converting Example: Chocolate Cake Recipe

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

Counting With Moles

o o You have 55.0 grams of CO 2 . How many moles?

To calculate how many moles of CO 2 you have, multiply the mass by a conversion factor.

o You can check your answer.

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.

Chemical Calculations

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

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

Chemical Calculations

o o Mass (of a reactant or product) = the # of moles in the balanced equation (Coefficient) x the molar mass.

Chemical Calculations - Stoichiometry 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.

• 2H 2 + O 2  2H 2 O Determine how many moles of water you are trying to make. • Convert the given mass (144g) of water into moles.

Chemical Calculations

Using Mole Ratios

 Write the conversion factors, or mole ratios.

 2H 2 + O 2  2H 2 O  Calculate how many moles of oxygen are required to produce eight moles of water.

Chemical Calculations

Converting Moles to Mass

 Convert

moles

using the of O

molar mass

conversion factor.

2 to

grams

of O 2 of O 2 as a by  To produce 144 grams of H 2 O, you must supply 128 grams of O 2 .

Assessment Questions

1.

Which of the following is a balanced chemical equation for the reaction of aluminum and ammonium perchlorate? a.

b.

c.

d.

Al + NH 4 ClO 4Al + 3NH 4 4 —› Al 2 O 3 ClO 4 + NH 4 Cl —› 4Al 2 O 3 + 3NH 4 Cl 8Al + NH 4 ClO 4 8Al + 3NH 4 ClO 4 —› 4Al 2 O 3 —› 4Al 2 O 3 + NH 4 Cl + 3NH 4 Cl

Assessment Questions

1.

Which of the following is a balanced chemical equation for the reaction of aluminum and ammonium perchlorate? a.

b.

c.

d.

Al + NH 4 ClO 4Al + 3NH 4 4 —› Al 2 O 3 ClO 4 + NH 4 Cl —› 4Al 2 O 3 + 3NH 4 Cl 8Al + NH 4 ClO 4 8Al + 3NH 4 ClO 4 —› 4Al 2 O 3 —› 4Al 2 O 3 + NH 4 Cl + 3NH 4 Cl 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 mol b.

5.85 mol c.

0.10 mol d.

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 mol b.

5.85 mol c.

0.10 mol d.

0.28 mol ANS: C

Assessment Questions

3.

In the reaction shown below, how many grams of hydrogen are produced when 10 moles of potassium react with water?

2K + 2H 2 O —› 2KOH + H 2 a.

2.5 g b.

5 g c.

d.

10 g 20 g

Assessment Questions

3.

In the reaction shown below, how many grams of hydrogen are produced when 10 moles of potassium react with water?

2K + 2H 2 O —› 2KOH + H 2 a.

2.5 g b.

5 g c.

d.

10 g 20 g ANS: C

Assessment Questions

1.

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

CH 4 + 2O 2 —› CO2 +2H 2 O True False?

ANS: False, products