th
Pre-Class:
I’m giving you back your Baking Soda/HCl Labs as these are good study tools for the core assessment. If you don’t understand why you got the grade you did, please talk to me after class. While I may not give you points, the important part is to be able to do this core assessment right.
FOR NOW: HAVE YOUR LAB MATERIALS READY TO GO.

• Finish lab.
• Finish limiting reagents.
• Discuss lab (kinda).
• Discuss core assessment.
• Old review (mole conversions and empirical/molecular formula).
• New review (stoichiometry, percent composition, limiting reagents).

• You will perform the “lab” portion with a partner of your choosing at your lab table.
– Speaking to anyone other than your lab partner
(and softly) is prohibited and will result in loss of points.
• When the lab portion is complete, you will complete the remainder at your desks individually.
• Grading is done on the district rubric.

• What to study?
– Your Baking Soda/HCl Lab
• Including the procedure
– Mole Conversions
– Mole Ratios and Stoichiometry
– Limiting Reagents and Percent Yield
– Writing, balancing, and identifying chemical reactions.

• To go from moles to grams you…
– Multiply by formula mass.
• To go from particles to moles you…
– Divide by Avogadro’s Number (6.02 x 10 23 ).
• To go from moles to liters you…
– Multiply by 22.4.
• To go from liters to grams, you…
– Convert liters to moles (divide by 22.4) and multiply by molar mass.

• Remember that an empirical formula is the most
“reduced” chemical formula possible.
• Another way to phrase it: It’s the lowest ratio between atoms in a formula.
• Example:
– Glucose is C
6
H
12
O
6
. That’s its molecular formula.
– Empirical formula: CH
2
O.
• If you need to, please take out my “directions” for solving these.
– Don’t have that anymore? It’s on my website.

• A compound was analyzed and found to contain 13.5g Ca, 10.8g O, and 0.675g H.
What is the empirical formula?
– First, convert each to moles.
• 0.337 mol Ca
• 0.675 mol O
• 0.668 mol H

• Next, select the smallest mole quantity and divide each by that number. This is the ratio part.
– 0.337 / 0.337 = 1 Ca
– 0.675 / 0.337 = 2 O
– 0.668 / 0.337 = 1.98 H = 2 H
• Last, since they’re all integers, let’s make the formula:
– CaO
2
H
2 or Ca(OH)
2

• NutraSweet is an artificial sweetener found in many processed foods in the grocery store.
Nutrasweet is 57.14 % C, 6.16% H, 9.52% N, and
27.18% O. The molar mass of Nutrasweet is 294 g/mol. What is the empirical formula and the molecular formula?
– First, convert each to moles. We’ll assume that we have 100 grams of Nutrasweet to make things easier.
• 57.14g C = 4.76 mol
• 6.16g H = 6.10 mol
• 9.52g N = 0.68 mol
• 27.18g O = 1.70 mol

• Next, divide each by the smallest number of moles.
– 4.76 / 0.68 = 7 C
– 6.10 / 0.68 = 8.97 = 9 H
– 0.68 / 0.68 = 1 N
– 1.70 / 0.68 = 2.5 O
• Oxygen is too far to round up or down, so we must multiply all numbers until they are each integers themselves.
• 2 is the best factor to eliminate a value of 0.5.

• Multiply each number by two to eliminate the decimal.
– 4.76 / 0.68 = 7 C * 2 = 14 C
– 6.10 / 0.68 = 8.97 = 9 H * 2 = 18 H
– 0.68 / 0.68 = 1 N * 2 = 2 N
– 1.70 / 0.68 = 2.5 O * 2 = 5 O
• Write the empirical formula:
– C
14
H
18
N
2
O
5

• But we’re not done! The problem wants us to find the molecular (real) formula too.
• First, find the molar mass of the empirical formula:
– Molar mass equals [approximately] 294 g/mol.
– Since our empirical formula has the same mass as the molecular formula, they are the same.
• In other cases, they may not be. Example next slide…

• If I were to have told you that the molecular formula was not 294 g/mol but instead was
882 g/mol.
– That would mean that the molecular formula weighed three times as much as the empirical formula.
– That would also mean that there were three times as many of each atom as before.
– Thus, the molecular formula would be C
42
H
54
N
6
O
15

• Chemical Reactions
– Balancing.
– Types.
– States of matter.
• Basic Stoichiometry
– Here is a quantity of a reactant. How much product could I produce? And vice versa…
• Percent Yield
– I could have produced that much, but I only produced this much. What percent is that?
• Limiting Reagents
– Here are two reactants. According to this reaction, which one will run out first? (that’s the limiter; the other is excess)

• Let’s go back to our “new review” type of problem.
– You write an answer, your partner writes an answer, and you both compare.

• What is the chemistry term for the process of calculating quantities in a chemical reaction?
– Stoichiometry

• What is the empirical formula of a compound whose molecular formula is C
13
H
52
O
26
?
– CH
4
O
2

• If a different compound with empirical formula CH
4
O
2 is determined in a lab to have a molar mass of 144 g/mol, what is its molecular formula?
– C
3
H
12
O
6

• What are the most likely products in this reaction:
• CH
4
+ O
– CO
2
2
 _________ and H
2
O

• What type of reaction is it?
• CH
4
+ O
2

– Combustion
_________

• Which two types of elements (must get both for credit) tend to do the replacing in a single replacement reaction?
– Metals and halogens

• BONUS NON-CHEMISTRY QUESTION
• You may wager any/all of your points.
• Category: Exploration
• Early explorers of North America, when not looking for the Fountain of Youth, were seeking to find a potential water route from the Atlantic
Ocean to the Pacific Ocean. What was the name they gave to this non-existent pathway?
– The Northwest Passage.

• In a reaction between two known quantities of reactants, what determines the amount of product formed?
– The limiting reagent/reactant.

• Water forms when hydrogen gas reacts with oxygen gas.
• What’s the skeleton equation?
– H
2
+ O
2
 H
2
O

• Water forms when hydrogen gas reacts with oxygen gas.
• What’s the balanced equation?
– 2H
2
+ O
2
 2H
2
O

• What kind of reaction was that?
– Synthesis or Combustion

• Which elements form diatomic molecules?
(need all for credit)
– Bromine
– Iodine
– Nitrogen
– Chlorine
– Hydrogen
– Oxygen
– Fluorine

• Which elements form diatomic molecules, and what does it mean to be diatomic? (need all elements and both answers for credit)
– Bromine
– Iodine
– Nitrogen
– Chlorine
– Hydrogen
– Oxygen
– Fluorine

• BONUS NON-CHEMISTRY QUESTION
• You may wager any/all of your points.
• Category: Currency
• What is the largest paper money bill currently printed by the U.S. Treasury?
– $100

• Okay, so this one isn’t really a question. It’s hard for me to put calculation problems up here, so let me give you one last set of worksheets.
• They’re the most involved of all the ones we’ve done, and so they make great study guides.
– Stoichiometry Review worksheet
– Unit 4 Monster Problem
• Please note that they are not sufficient study materials on their own.