Name KEY Period. CRHS Academic Chemistry Unit 7 - Chemical Quantities. Practice Problems. Due Date Assignment On-Time (100) Late (70)

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1 Name KEY Period CRHS Academic Chemistry Unit 7 - Chemical Quantities Practice Problems Due Date Assignment On-Time (100) Late (70) Warm-Up EC Notes, Homework, Exam Reviews and Their KEYS located on CRHS Academic Chemistry Website:

2 Page 2 of 16 Unit 7 HW Day 1 Day 7 Day 2 Day 8 Day 3 Day 9 Day 4 Day 10 Day 5 Day 11 Day 6 Day 12

3 HW 7.1 INTRODUCTION TO THE MOLE Unit 7 HW Page 3 of 16 Find the molar mass of the compound. Round average atomic mass to the hundredths place. Show work and units. 1. NaCl 2. Ca(OH)2 Na = Ca = 1(40.078) = Cl = O = 2(15.999) = NaCl = g/mol H = 2(1.008) = Ca(OH)2 = g/mol 3. Fe2O3 4. Ammonium phosphate (NH4)3PO4 Fe = N = O = H = g/mol P = O = g/mol 5. Al2(SO4)3 6. Dinitrogen trioxide N2O3 Al = N = S = O = O = g/mol g/mol 7. An alien visits earth. He brings with him an unknown substance. He says, I believe this substance is like an Earthly compound; it is either like nitrogen dioxide or nitrogen trioxide. I m not sure which. All I know is that its molar mass is g. Which compound did the alien bring with him? Show your work to receive credit. NO3 is unknown gas

4 Page 4 of 16 Unit 7 HW HW 7.2 MOLE TO MASS AND MASS TO MOLE CONVERSIONS Complete the following conversions using dimensional analysis. Show work! 1. Convert mol of calcium cyanide, Ca(CN)2, to mass. Ca = 1(40.078) = C = 2(12.011) = N = 2( = g/mol mol Ca(CN) 2 x g Ca(CN) 2 1 mol Ca(CN) 2 = = g Ca(CN) 2 2. How many grams are in 0.50 mol of copper (II) sulfate? CuSO4 Cu = S = O = g/mol Answer = 8.0x10 g CuSO4 3. Convert 30 g of silicon dihydride to moles. SiH2 Si = H = g/mol Answer = 1 mol SiH 2 4. How many moles are in 100 grams of potassium sulfide? K2S K = 2(39.098) = S = 1(32.066) = g/mol 100 g x 1 mol = mol = 0.9 mol K2S g 5. Your grandfather has to take 5 grams of aspirin (C 8H8O4) daily for his arthritis. How many moles of aspirin should he take? C = 8(12.011) = H = 8(1.008) = O = 4(15.999) = g/mol 5 g x 1 mol g = mol = mol C 8 H 8 O 4

5 Unit 7 HW Page 5 of You go to the pawn shop to buy your girlfriend some jewelry. The clerk offers to sell you a necklace that has 5 grams of gold in it for $300. How many moles of gold are in the necklace? 5 g x 1 mol Au g Au = mol Au = mol Au 7. You are conducting a lab experiment to evaluate the reaction between calcium hydroxide and hydrochloric acid. Your teacher has told you how much of each reactant to use (in moles). You must convert to mass before you can start. Complete the table and show work below the table. Name of Compound Formula of Compound Molar Mass Moles Needed Mass Needed calcium hydroxide Ca(OH) g 2.00 mol 148 g hydrochloric acid HCl g 4.00 mol 146 g Ca(OH) 2 Ca = 1(40.078) = O = 2(15.999) = H = 2(1.008) g g/mol 2.0 mol x = g = 148 g 1 mol HCl H = Cl = g g/mol 4.0 mol x = g = 146 g 1 mol

6 Page 6 of 16 HW 7.3 REPRESENTATIVE PARTICLES Unit 7 HW Complete the following conversions using dimensional analysis. Show work! 1. How many moles are in 1.50 x molecules of nitrogen trihydride? 1.50x10 23 molecules x 1 mol 6.02x10 23 molecules = mol = mol 2. Convert 4.8 moles of calcium carbonate to formula units. 4.8 mol x 6.02x1023 formula units 1 mol = x10 24 formula units = 2. 9x10 24 formula units 3. How many molecules are in 4.80 x 10 3 mol bromine gas? 4.80x10 3 mol x 6.02x1023 molecules 1 mol = x10 21 molecules = 2. 89x10 21 molecules Br 2 4. There are moles in 3.73 x formula units of barium chloride. 1 mol 3.73x10 22 formula units x = mol BaCl 6.02x10 23 formula units 2 = mol BaCl 2 5. Your doctor prescribes you lithium carbonate for your bipolar disorder. Examine the prescription below. How many formula units of lithium carbonate will you ingest each day? 5 mol x 6.02x1023 formula units 1 moll = 3.01x10 24 formula units = 3x10 24 formula units of Li 2 CO 3 Dr. Emilio Avogadro Date Oct 23, 2012 Patient: Kim Estudiante : Take 5 mol Lithium Carbonate Once daily at bedtime Signature E. Avogadro

7 Unit 7 HW Page 7 of The same pawn shop clerk from HW 6.2 says, Okay, you don t like that necklace? How about these earrings? They have 1.00 x atoms of gold in them! How many moles of gold is this? Answer = mol Au 7. A cold pack uses an endothermic reaction to cool its surroundings. Inside a cold pack are 5.33 x formula units of ammonium nitrate. How many moles of ammonium nitrate are in a cold pack? Answer = = mol NH 4 NO 3

8 Page 8 of 16 HW 7.4 MIXED MOLE CONVERSIONS Unit 7 HW Complete the following conversions using dimensional analysis. Show work! 1. Convert 3.33 x atoms of sodium to grams. 3.33x10 24 Na atoms x 1 mol Na 6.02x Na atoms g Na x = g Na = 127 g Na 1 mol Na 2. There are moles in 187 g aluminum. 1 mol Al 187 g Al x = mol Al = mol Al g Al 3. How many grams are in 40 moles of ammonium chloride NH4Cl N = H = 4(1.008) = Cl = g NH4Cl/1 mol NH4Cl 40 mol NH 4 Cl x 53,492 g NH 4 Cl 1 mol NH 4 Cl = 2139 g NH 4 Cl = 2000 g NH 4 Cl 4. How many moles are in 333 g tin (II) fluoride? SnF2 Sn = F = 2(18.998) = g SnF2/1 mol SnF2 333 g SnF 2 x 1 mol SnF g SnF 2 = mol SnF 2 = mol SnF 2 5. Convert 5.00 x molecules hydrogen (H2) to grams. H 2(1.008) = g H2/1 mol H2 5.00x10 25 molecules H 2 x 1 mol H x10 23 molecules H 2 x g H 2 1 mol H 2 = g H 2 = 167 g H 2

9 Unit 7 HW Page 9 of In 1970, Nobel Prize winning scientist Linus Pauling recommended taking megadoses of vitamin C to ward off the common cold. He suggested taking up to 2.5 grams per day. How many molecules of vitamin C (C 6 H 8 O 6 ) did he recommend that you should take per day? C = H = O = g Vit C/ 1 mol Vit C Answer = = 8. 5x10 21 molecules Vit C 7. Have you ever tried the energy drink Crunk!!!? It s made by Lil Jon (the rapper) and it is so yummy! It even has 62.0 grams of amazing sugar (C 12 H 22 O 11 ) per can! That s like molecules of sugar! Answer = 1. 09x10 23 molecules C 12 H 22 O 11

10 Page 10 of 16 Unit 7 HW HW 7.5 PERCENT COMPOSITION 1. Write the formula for percent composition below. Use the formula and the information given in subsequent questions to complete this assignment. % composition = Total mass of element Molar mass of Compound x 100% 2. Find the percent composition of hydrogen in each compound: a) Ca(OH) 2 % of H = 2.721% Ca = O = 2(15.999)= Molar Mass = g/mol %H = x 100 = 2.721% H=2(1.008) = b) C 2 H 6 % of H = 20.11% c) Al (C 2 H 3 O 2 ) 3 % of H = _4.445% 3. Find the percent composition of each element in these compounds: a) NaCl molar mass = g/mol % of Na = _39.34% %Na = % of Cl = 60.66% %Cl = Na molar mass = g/mol Cl molar mass = g/mol x 100% = 39.34% x 100% = 60.66% b) (NH4)2S molar mass = % of N = % of H = % of S = 47.06%

11 Unit 7 HW Page 11 of A sample of liquid with a mass of grams was decomposed into its elements and gave grams of carbon, grams of hydrogen, and grams of oxygen. What is the percent composition of this oxygen in this compound? (hint: you don t need to calculate molar mass to solve this problem, just use the formula from question #1) %O = x 100% = 28.62% O 5. A quantitative analysis of grams of an unknown solid found grams of carbon, grams of hydrogen and grams of oxygen. Calculate the percent composition of carbon in this compound. (hint: you don t need to calculate molar mass to solve this problem, just use the formula from question #1) Answer = 42.10% C 6. What is the percentage of Fe in FeCO3? Answer = % Fe

12 Page 12 of 16 HW 7.6 EMPIRICAL FORMULA Unit 7 HW Answer the following questions concerning empirical formulae. Use the steps outlined in your notes. 1. Determine the empirical formula for a compound containing grams potassium and 4.00 grams oxygen. Step g K x 1 mol K = mol K g K 4.00 g O x 1 mol O = 0.25 mol O g O Step mol K 0.25 mol = 2 K Step 3 - K 2 O 0.25 mol O = 1.00 O 0.25 mol 2. A compound contains grams of iron and grams of oxygen. Construct the empirical formula. 1 mol Fe g Fe x g Fe = 3.12 mol Fe 3.12 mol Fe = 1 mol Fe x 2 = 2 mol Fe 3.12 mol 1 mol O g O x g O = 4.63 mol O 4.63 = x 2 = 3 mol O 3.12 Fe 2 O 3 3. Sodium sulfite is a meat preservative and sodium sulfate is a laxative. Your grandmother gives you a side of beef for your birthday and you d like to keep it from rotting. You ve found a sample of a compound of sodium that contains 36.5 grams of sodium, 25.4 grams of sulfur, and 38.1 grams of oxygen. Do you have a laxative or the meat preservative you so desperately need? Sodium Sulfite Na2SO3 Sodium Sulfate = Na2SO4 Na2SO3 = Sodium Sulfite = Preservative

13 Unit 7 HW Page 13 of As lead arson investigator with the Houston Fire Department you find a small sample of the accelerant (fuel) that caused a fire that took the lives of 11 people in an urban apartment complex. You run the sample through a mass spectrometer and find that it contains 37.5% carbon, 12.5% hydrogen, and 50.0% oxygen, by mass. Determine the empirical formula of this substance. CH 4 O

14 Page 14 of 16 HW 7.7 MOLECULAR FORMULA Unit 7 HW Answer the following questions concerning molecular formulae. Use the steps outlined in your notes. Show work 1. Find the molecular formula for a compound with a molar mass of g/mol and an empirical formula of CHO2. Step 1: Mass of CH02 = 1 x x x = Step 2: Scale factor = Mass of Molecule / Mass of Empirical Formula = 90.04/45.02 = 2 Step 3: Scale Factor x Empirical Formula = 2 x CHO2 = C 2 H 2 O 4 is molecular formula 2. Find the molecular formula for a compound with 46.68% nitrogen and 53.32% oxygen and a molar mass of g/mol g N x 1 mol N = 3.33 mol N 3.33 mol N = 1 mol N g N 3.33 mol 1 mol O g O x g O = 3.33 mol O 3.33 Mol O = 1 mol O 3.33 NO is Empirical Formula. Mass of NO = = g/mol Scale = /30.01 = 2 Molecular Formula is 2 x NO = N 2 O 2 N 2 O 2 3. Elaidic acid is the primary trans fatty acid present in partially hydrogenated oils used in food production. Calculate the molecular formula for elaidic acid given that it has an empirical formula of C 9H17O1 and a mass of 282 g/mol. C 18 H 34 O 2 4. Strychnine, a deadly poison, has a mass of 334 g/mol and a percentage composition of 75.42% carbon, 6.63% hydrogen, 8.38% nitrogen, and 9.57% oxygen. What is the molecular formula of strychnine? C 21 H 22 N 2 O 2

15 Unit 7 HW Page 15 of 16 Common Polyatomic Ions List 20 Name Common Polyatomic Ions Ion Name Ion acetate C 2 H 3 O 2 or CH 3 COO hypochlorite ClO ammonium + NH 4 nitrate NO 3 carbonate 2 CO 3 nitrite NO 2 chlorate ClO 3 perchlorate ClO 4 chlorite ClO 2 permanganate MnO 4 chromate 2 CrO 4 phosphate 3 PO 4 cyanide CN phosphite 3 PO 3 dichromate 2 Cr 2 O 7 silicate 2 SiO 3 hydrogen carbonate HCO 3 sulfate 2 SO 4 hydroxide OH sulfite 2 SO 3 How to key scientific notation into a TI calculator: Type in 6.02 x : Should display: How to key molar mass into a TI calculator in ONE STEP!: Example: Na 2 SO 4 Roman Numerals for Transition Metals = I 2 = II 3 = III 4 = IV 5 = V 6 = VI

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