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Bell Ringer. What is a Mole? What is the mass of a NaCl molecule?. Chapter 7.1b. Molar Mass. 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. - PowerPoint PPT PresentationTRANSCRIPT
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