1. Chapter 12 Chemical Quantities
12.2 Using Moles

2. Warm-up: Making a Sandwich
How Many Sandwiches?

3. What is Stoichiometry?
Stoichiometry is the study of quantitative relationships between amounts of reactants used and products formed by a chemical reaction.
A balanced chemical equation is needed to solve any stoichiometry problem

4. Practical Applications of Stoichiometry
In a spacecraft, the carbon dioxide exhaled by astronauts can be removed by its reaction with lithium hydroxide, LiOH, according to the following chemical equation.
CO2(g) + 2LiOH(s) Li2CO3(s) + H2O(l)
How many moles of lithium hydroxide are required to react with 20 mol of CO2, the average amount exhaled by a person each day?

5. Strategy – Relate everything to the mole
The mole is the common thread that links reactants to products.
1CO2(g) + 2LiOH(s) 1Li2CO3(s) + 1H2O(l)
Mole Ratios

6. The Mole Super Highway

7. Practice Problems – Mole to Mole
Balanced
Chemical Equation
How many moles of water are formed when 3.8 moles of Hydrogen react with an excess of Oxygen?
2 𝐻 2 + 𝑂 2 →2 𝐻 2 O
How many moles of oxygen are needed to fully combust 1.6 moles of ethane(C2H6)?

8. Warm-up
Felix has six of the same Charazard cards. For every 3 Charazard cards that he trades in, he can get one Arcanine cards. Each Arcanine card is valued at $ How much money can Felix make from a trade if he trades in all of his Charazard cards?

9. Practice Problems – Mole to Mass
How many grams of water are formed when 4.5 moles of oxygen react with an excess of hydrogen?
2 𝐻 2 + 𝑂 2 →2 𝐻 2 O
How many moles of oxygen are needed to produce 15.6g of carbon dioxide?

10. Practice Problems – Mass to Mass
How many grams of water are formed when 18.6 grams of oxygen react with an excess of hydrogen?
2 𝐻 2 + 𝑂 2 →2 𝐻 2 O
How many grams of ethane are needed to produce 23.4g of water?

11. Warm-up At STP, which of the following would have the greatest volume?
1mole = NO
1mole = He
1mole = CH4

12. Practice Problems – Volume at STP
How many liters of oxygen are required to react with 5.6 liters of hydrogen to produce water at STP?
2 𝐻 2 + 𝑂 2 →2 𝐻 2 O

13. Solving for Volume without STP Conditions
When a chemical reaction is carried out under conditions other than STP, the ideal gas law equation must be used.
PV=nRT is the Ideal Gas Law Equation where….
P = pressure
V = volume
n = moles
R = gas constant = 𝐿.𝑘𝑃𝑎 𝐾.𝑚𝑜𝑙 = 𝐿.𝑎𝑡𝑚 𝐾.𝑚𝑜𝑙
T = temperature in Kelvin

14. Practice Problems – Ideal Gas Law
PV=nRT R = gas constant = 𝐿.𝑘𝑃𝑎 𝐾.𝑚𝑜𝑙 = 𝐿.𝑎𝑡𝑚 𝐾.𝑚𝑜𝑙
What volume of carbon dioxide can be produced from 1.2 moles of ethane gas at 200K and 0.65 atm?

15. Warm-up
You mix together the ingredients to make a batch of chocolate chip cookies. The recipe says that the yield should be 3 dozen cookies. You only get 30 cookies. What percentage of the expected yield did you get?

16. Percent Yield
Stoichiometric calculations provide a theoretical yield or maximum amount of product that can be produced from a given amount of reactants.
The actual yield is the amount that is actually produced when a reaction is carried out.
The percent yield reflects the ratio of the theoretical and actual yields

17. Practice Problem - Percent Yield
When 4.3 grams of sodium are combined with aluminum nitrate in the following equation, 1.52g of aluminum are produced. What is the percent yield of aluminum?
3𝑁𝑎+𝐴𝑙(𝑁 𝑂 3 ) 3 →𝐴𝑙+3𝑁𝑎𝑁 𝑂 3

18. Warm-up
What percentage of the students in this classroom are girls?

19. Percent Composition by Mass
The total mass of each individual element in a compound divided by the total mass of the compound
What is the percent composition of Mg(BrO4)2?
Remember how to calculate molar mass…..
1(mass Mg) + 2(mass of Br) + 8(mass of oxygen) = Mass of Mg(BrO4)2

20. Warm-up
Simplify the following fractions.

21. Empirical Formula
Chemical formula which contains the lowest whole number ratio of atoms
Ionic formulas always contain the lowest whole number ratios
Covalent compounds do not always contain the lowest whole number ratios
What is the Empirical Formula of the following compounds?
C6H12O6
C3H9O6
H2O2

22. Determining the Empirical Formula of a Compound
NxOy
What is the empirical formula for a compound which contains 25.9% nitrogen and 74.1% oxygen by mass?
Covert % to mass (if needed)
Convert mass to moles
Divide each molar quantity by the lowest number of moles
Multiply by the smallest number needed to create a whole number ratio (if needed)
Assume a 100g sample. In that sample 25.9 g is nitrogen and 74.1g is oxygen
N1.85O4.63
N1O2.5
N2O5
N1x2O2.5x2

23. Which of the following are empirical formulas?
Warm-up
Which of the following are empirical formulas?
C2H8
C2H8N2
H3PO4
C8H12O4
Li2SO4
CH4

24. Molecular Formulas Empirical Formula = 𝐶 𝐻 2 O
Many chemicals can have the same empirical formula because atoms can share electrons in many ways.
𝐶 6 𝐻 12 𝑂 6
Glucose
𝐶 2 𝐻 4 𝑂 2
Acetic Acid
Empirical Formula = 𝐶 𝐻 2 O

25. Simple Molecular Problems
What is the molecular formula of a compound with an empirical formula of CH2O and a molecular mass of 90g/mol?
Determine the empirical mass
Divide the molecular mass by the empirical mass to determine how much larger the mass of the molecule is compared to the empirical formula
Multiple the subscripts of each element in the empirical formula by the factor determined in #2
CH2O =1(12g)+2(1g)+1(16g) = 30g
C3H6O3
C1x3H2x3O1x3

26. Longer Molecular Problems
Determine the empirical formula
Given the molecular mass, determine the molecular formula
Determine the molecular formula of a compound that has a mass of 34g and contains 94.1% oxygen and 5.9% hydrogen by mass.