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.
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 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 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.
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