Chemistry 121

1
Chemistry 121

• Week 2

2
Check-in

• Aluminum oxide, Al2O3, also known as corundum,
  comprises the gemstones ruby and sapphire.  What
  is the molar mass of Al2O3?

3
Why use moles?

• Equal mass ? equal of particles
• Atoms/moles represented in formula, not mass

4
Check-in, cont.

• How many moles of Al2O3 are present in an
  8.62-carat ruby?  1 carat 0.2 g
• How many O atoms are present in the 8.62-carat
  ruby?

5
Check-in, cont.

• The red color of rubies is due to a small number
  of Cr3 ions taking the place of Al3 ions in
  Al2O3.  Is ruby an example of a mixture or a
  substance and why?

6
Mass-mole-number relationships
7

• Original Nestlé Toll House Chocolate Chip Cookies
  Estimated Times Preparation - 15 min Cooking
  - 9 min Cooling Time - 15 min cooling Yields
  - 60 Ingredients
• 2 1/4 cups all-purpose flour
• 1 teaspoon baking soda
• 1 teaspoon salt
• 1 cup (2 sticks) butter, softened
• 3/4 cup granulated sugar
• 3/4 cup packed brown sugar
• 1 teaspoon vanilla extract
• 2 large eggs
• 2 cups (12-oz. pkg.) NESTLÉ TOLL HOUSE
  Semi-Sweet Chocolate Morsels
• 1 cup chopped nuts
• DirectionsPREHEAT oven to 375 F.COMBINE
  flour, baking soda and salt in small bowl. Beat
  butter, granulated sugar, brown sugar and vanilla
  extract in large mixer bowl until creamy. Add
  eggs, one at a time, beating well after each
  addition. Gradually beat in flour mixture. Stir
  in morsels and nuts. Drop by rounded tablespoon
  onto ungreased baking sheets. BAKE for 9 to 11
  minutes or until golden brown. Cool on baking
  sheets for 2 minutes remove to wire racks to
  cool completely.

8
Cookie recipe stoichiometry
1 egg 1 stick butter 1c flour 1c
sugar 1c chocolate chips 30
cookies

(1 batch)




9
Cookie recipe stoichiometry
balanced reaction
1 egg 1 stick butter 1c flour 1c
sugar 1c chocolate chips 30 cookies




How many cookies can I make if I have 1 dozen
eggs 4 sticks of butter 6 cups of flour 6 cups
of sugar 3 cups of chocolate chips
actual ingredients
?
10
Cookie recipe stoichiometry
balanced reaction
1 egg 1 stick butter 1c flour 1c
sugar 1c chocolate chips 30 cookies




actual ingredients
?
90 cookies (3 batches)
What will be left over?
11
In our cookie reaction

• The chocolate chips are the limiting reactant (or
  reagent)
• They limit the number of cookies (amount of
  product) we can make
• The other ingredients are present in excess
• There will be some amount of material left over
  once all the possible product is made
• Law of mass conservation?

12
Check-in

• An Alka-Seltzer tablet contains 1.95 g of sodium
  bicarbonate (NaHCO3).  How many moles of sodium
  bicarbonate are present in two Alka-Seltzer
  tablets (a typical dose)?

13
Check-in

• If two Alka-Seltzer tablets are placed in an
  excess of water (sodium bicarbonate is the
  limiting reagent), how many moles of CO2 gas will
  be produced?
• NaHCO3 (s)    C6H8O7 (s)  ?    H2O (l)     CO2
  (g)     NaC6H7O7 (aq)

14
Check-in

• Why are these two reactions (the volcano and
  the Alka-Seltzer) so similar?

15
Check-in

• K2CO3    2  NH4NO3  ?   2 KNO3    CO2   
  H2O    NH3
• DirectionsMix 1 kg K2CO3 and 2 kg NH4NO3  CO2 
  and  NH3 come off as gases and water can be
  evaporated leaving pure product. 
• Is this correct?

16
Check-in

• What is the molarity of a solution that contains
  75 g K2CO3 in enough water to make 300. mL of
  solution?

17
Making solutions
http//www.naugraexport.com/glass/flask-v-1.jpg
18
Check-in

• If the solution above was diluted to 1.50 L, what
  would the concentration (in molarity) of K2CO3 be?

19
(No Transcript)
20
(No Transcript)