Today is Friday (!),May 4th, 2018

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.

Today’s Agenda

• Review and stuff.

Core Assessment Details

• 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.

Core Assessment Details

• 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.

Mole Conversion 1-Slide Review

• 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 1023).

• 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.

Empirical Formula

• Remember that an empirical formula is the most “reduced” chemical formula possible.

• Another way to phrase it: It’s the lowest ratiobetween atoms in a formula.

• Example:– Glucose is C6H12O6. That’s its molecular formula.– Empirical formula: CH2O.

• If you need to, please take out my “directions” for solving these.– Don’t have that anymore? It’s on my website.

Empirical Formula Example #1

• 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

Empirical Formula Example #1

• 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:– CaO2H2 or Ca(OH)2

Empirical Formula Example #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

Empirical Formula Example #2

• 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.

Empirical Formula Example #2

• 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:

– C14H18N2O5

Empirical Formula Example #2

• 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…

Empirical Formula Problem #2

• If I were to have told you that the molecular formula was not 294 g/mol but instead was882 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 C42H54N6O15

Other Stuff to Review

• 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)

And now…

• Let’s go back to our “new review” type of problem.

– You write an answer, your partner writes an answer, and you both compare.

Review Question 1

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

– Stoichiometry

Review Question 2

• What is the empirical formula of a compound whose molecular formula is C13H52O26?

– CH4O2

Review Question 3

• If a different compound with empirical formula CH4O2 is determined in a lab to have a molar mass of 144 g/mol, what is its molecular formula?

– C3H12O6

Review Question 4

• What are the most likely products in this reaction:

• CH4 + O2 _________

– CO2 and H2O

Review Question 5

• What type of reaction is it?

• CH4 + O2 _________

– Combustion

Review Question 6

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

– Metals and halogens

Review Question 7

• 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.

Review Question 8

• In a reaction between two known quantities of reactants, what determines the amount of product formed?

– The limiting reagent/reactant.

Review Question 9

• Water forms when hydrogen gas reacts with oxygen gas.

• What’s the skeleton equation?

– H2 + O2 H2O

Review Question 10

• Water forms when hydrogen gas reacts with oxygen gas.

• What’s the balanced equation?

– 2H2 + O2 2H2O

Review Question 11

• What kind of reaction was that?

– Synthesis or Combustion

Review Question 12

• 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

Review Question 13

• 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

Review Question 14

• Here’s a balanced molecular equation:

• Ni(NO3)2 (aq) + 2NaOH (aq) Ni(OH)2 (s) + 2Na(NO3)2 (aq)

• What is the net ionic equation?

– Ni2+ (aq) + 2OH- (aq) Ni(OH)2 (s)

Review Question 15

• 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 and Review

• Please note that they are not sufficient study materials on their own.