1. Unit 9: More fun with Stoichiometry
Molarity

2. Special cases for gas stoichiometry
@STP:
1 mole = 22.4 L
Ex: 100. g of nitrogen are collected at STP, what volume would it occupy?
m=100. g
V=?
L/mol
g-MMN2=28.0 g

3. Special cases for gas stoichiometry
What is Avogadro’s Law (hypothesis)?
“Equal volumes of gases under the same conditions of temperature and pressure contain equal numbers of particles.”
That means in reactions between gases under similar conditions, the gases will combine in volume ratios equal to the coefficients in the balanced chemical equation.
Ex: Nitrogen and hydrogen combine to form ammonia. If 10. L of nitrogen combines with an excess of hydrogen, how many liters of hydrogen will be consumed and how many liters of ammonia will be formed?
V=10.L V=? V=?

4. What is a mole? Mole: Amount of a substance A number!
1 mol = 6.02 x 1023 things
How do we count a mole?
We don’t

5. What is a mole? We can count by massing
Ex: How many iron atoms are in 100. g of Fe?
n=?
m=100.g
MM=55.8g/mol

6. What is a mole? We can count by volume of a gas.
Ex: How many chlorine molecules are in 11.2 L at STP?
n=?
V=11.2L

7. Solutions Made of solvent and solute(s)
Draw a particle model of 0.5 g of CaCl2 dissolved in 100 ml of water.
Draw a particle model of 1.0 g of CaCl2 dissolved in 100 ml of water.
What’s different?

8. Solutions
How could we describe the number of moles of salt in the solution?
Molar concentration
Ratio of moles to volume
Molarity (M)
Molarity is very useful because now we can count by volume as well as massing
Ex: Find the molarity when 1.0 g of K2Cr2O7 is dissolved in 100 mL of water.
m=1.0 g
MM=294.2g/mol
V=100. mL=0.100 L
M=?

9. Assignment
Unit 9 WS #3
Unit 9 test next Thurs/Fri