Name Date Class. representative particle molar mass representative particles

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1 10.1 THE MOLE: A MEASUREMENT OF MATTER Section Review Objectives Relate Avogadro s number to a mole of a substance Calculate the mass of a mole of any substance Describe methods of measuring the amount of something Compare and contrast the atomic mass of an element and its molar mass Vocabulary mole (mol) Avogadro s number representative particle molar mass Key Equations moles representative particles representative particles moles 1 mole representative particles representative particles 1 mole Part A Completion Use this completion exercise to check your knowledge of the terms and your understanding of the concepts introduced in this section. Each blank can be completed with a term, short phrase, or number. Chemists relate units of counting, of mass, and of volume to a 1. single quantity called the 1. The number of representative 2. particles in a mole of a substance is To find the mass of a mole of a compound, scientists add 4. together the 3 of the atoms making up the compound. 5. When you substitute the unit grams for amu, you obtain the 4 of the compound. There are in a mole of any substance. 5 representative particles Chapter 10 Chemical Quantities 241

2 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 6. A mole of a pure substance contains atoms. 7. The representative particle of a compound is the molecule. 8. A mole of CCl 4 is composed of one atom of carbon and four atoms of chlorine. 9. A mole of carbon atoms has a mass approximately three times as great as the mass of a mole of helium atoms. 10. The molar mass of nitrogen gas is 14.0 g. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B Avogadro s number molar mass mole representative particles a. the atoms, molecules, or ions present in a substance b c. the mass of one mole of a substance d. SI unit that measures the amount of a substance Part D Problems Solve the following problems in the space provided. Show your work. 15. How many moles of Pb is atoms of Pb? 16. What is the molar mass of ethane, C 2 H 6? 17. Find the mass of mol K 2 SO How many representative particles are in 2.5 mol H 2 O 2? 242 Core Teaching Resources

3 10.2 MOLE-MASS AND MOLE-VOLUME RELATIONSHIPS Section Review Objectives Convert the mass of a substance to the number of moles of a substance, and the number of moles of a substance to mass Calculate the volume of a quantity of gas at STP Vocabulary Avogadro s hypothesis standard temperature and pressure (STP) molar volume Key Equations mass (grams) number of moles moles mass (grams) grams grams 22.4 L mole L 1 mole 1 mole mass (grams) mass (grams) 1 mole volume of gas moles of gas Part A Completion Use this completion exercise to check your knowledge of the terms and your understanding of the concepts introduced in this section. Each blank can be completed with a term, short phrase, or number. At STP (0 C and 1 atmosphere pressure), one mole of any gas 1. occupies a volume of 1 L. This quantity is known as the 2. 2 of the gas. To determine the volume in liters of 2.00 mol 3. of SO 2 gas at STP, you would use 3 as a conversion factor L 1 mole, expressed in the units g/l, is used as a conversion factor 5. when converting from volume to molar mass. When converting between numbers of representative particles, masses, and volumes, you must always convert to 5 as an intermediate step. Chapter 10 Chemical Quantities 243

4 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 6. One mole of any gas occupies a volume of 22.4 L. 7. For a substance of known molar mass, the number of moles of a sample can be calculated from the mass of the sample. 8. The volume occupied by one mole of a gas is dependent on the molar mass of the gas. 9. The volume of a gas at STP can be calculated from the number of molecules of the gas. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B 10. molar mass 11. standard temperature 12. molar volume 13. standard pressure a L of a gas at STP b kpa or 1 atm c. 0 C d. mass (in grams) of one mole of a substance 14. molar road map Part D Problems Solve the following problems in the space provided. Show your work. 15. What is the density of N 2 O, a gas, at STP? 16. What is the mass of two moles of NaCl? 17. How many moles are in 16 grams of O 2? e. a means of relating mass, number of representative particles, and gaseous volume of a substance 18. What is the volume of 16 grams of O 2 at STP? 244 Core Teaching Resources

5 10.3 PERCENT COMPOSITION AND CHEMICAL FORMULAS Section Review Objectives Calculate the percent by mass of an element in a compound Interpret an empirical formula Compare and contrast empirical and molecular formulas Vocabulary percent composition empirical formula Key Equation mass of element % mass of element 100% mass of compound Part A Completion Use this completion exercise to check your knowledge of the terms and your understanding of the concepts introduced in this section. Each blank can be completed with a term, short phrase, or number. The 1 of a compound is the percent by mass of each 1. element in a compound. The percent by mass of an element in a 2. compound is the number of grams of the element per 2 g 3. of the compound, multiplied by 100%. To calculate the percent by 4. mass of an element in a known compound, divide the mass of the 5. element in one mole by the 3 and multiply by 100%. 6. A(n) 4 formula represents the lowest 5 ratio of the elements in a compound. It can be calculated from a compound s percent composition. The 6 formula of a compound is either the same as its empirical formula, or it is some whole-number multiple of it. Chapter 10 Chemical Quantities 245

6 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 7. It is necessary to know the formula of a compound in order to calculate its percent composition. 8. If the percent by mass of carbon in methane, CH 4, is 75%, then 100 grams of methane contain 25.0 grams of hydrogen. 9. The formula for methane, CH 4, is both a molecular and an empirical formula. 10. The empirical formula for glucose, C 6 H 12 O 6, is C 2 H 4 O 2. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B 11. percent composition 12. empirical formula 13. molecular formula a. describes the actual number of atoms of each element in a molecule of a compound b. the lowest whole-number ratio of atoms of the elements in a compound c. the percent by mass of each element in a compound Part D Problems Solve the following problems in the space provided. Show your work. 14. What is the percent composition of each of the following? a. Cr 2 O 3 c. HgS b. Mn 2 P 2 O 7 d. Ca(NO 3 ) Determine the empirical formula of the compound with the percent composition of 29.1% Na, 40.5% S, and 30.4% O. 16. How many kilograms of iron can be recovered from 639 kilograms of the ore Fe 2 O 3? 246 Core Teaching Resources

7 10 CHEMICAL QUANTITIES Practice Problems In your notebook, solve the following problems. SECTION 10.1 THE MOLE: A MEASUREMENT OF MATTER 1. What is the molar mass of sucrose (C 12 H 22 O 11 )? 2. What is the molar mass of each of the following compounds? a. phosphorus pentachloride (PCl 5 ) b. uranium hexafluoride (UF 6 ) 3. Calculate the molar mass of each of the following ionic compounds: a. KMnO 4 b. Ca 3 (PO 4 ) 2 4. How many moles is molecules of water? 5. How many atoms of zinc are in 0.60 mol of zinc? 6. What is the mass of 1.00 mol of oxygen (O 2 )? SECTION 10.2 MOLE MASS AND MOLE VOLUME RELATIONSHIPS 1. What is the molar mass of each of the following compounds? a. C 6 H 12 O 6 b. NaHCO 3 c. C 7 H 12 d. KNH 4 SO 4 2. Calculate the mass in grams of each of the following: a. 8.0 mol lead oxide (PbO) d mol molecular oxygen (O 2 ) b mol hydrogen sulfide (H 2 S) e mol ethylene glycol (C 2 H 6 O 2 ) c mol silicon tetrahydride (SiH 4 ) 3. How many grams are in 1.73 mol of dinitrogen pentoxide (N 2 O 5 )? 4. How many grams are in mol of calcium phosphate [Ca 3 (PO 4 ) 2 ]? 5. Calculate the number of moles in each of the following: a g sodium bromide (NaBr) d g monochloromethane (CH 3 Cl) b g magnesium nitrate [Mg(NO 3 ) 2 ] e g propylene glycol [C 3 H 6 (OH) 2 ] c g magnesium chloride (MgCl 2 ) 6. A chemist plans to use grams of ammonium nitrate (NH 4 NO 3 ) in a reaction. How many moles of the compound is this? 7. A solution is to be prepared in a laboratory. The solution requires mol of quinine (C 20 H 24 N 2 O 2 ). What mass, in grams, should the laboratory technician obtain in order to make the solution? Chapter 10 Chemical Quantities 247

8 8. What is the volume at STP of 2.66 mol of methane (CH 4 ) gas? 9. How many moles is 135 L of ammonia (NH 3 ) gas at STP? 10.3 PERCENT COMPOSITION AND CHEMICAL FORMULAS 1. A sample of a compound analyzed in a chemistry laboratory consists of 5.34 g of carbon, 0.42 g of hydrogen, and g of chlorine. What is the percent composition of this compound? 2. Find the percent composition of a compound containing tin and chlorine if g of the compound contains 5.74 g of tin. 3. If g of carbon combines completely with g of hydrogen to form a compound, what is the percent composition of this compound? 4. From the formula for calcium acetate, Ca(C 2 H 3 O 2 ) 2, calculate the mass of carbon that can be obtained from 65.3 g of the compound. 5. How many grams of aluminum are in 25.0 g of aluminum oxide (Al 2 O 3 )? 6. How many grams of iron are in 21.6 g of iron(iii) oxide (Fe 2 O 3 )? 7. Determine the empirical formula of each of the following compounds from the percent composition: a. 7.8% carbon and 92.2% chlorine b. 10.0% C, 0.80% H, 89.1% Cl 248 Core Teaching Resources

9 10 INTERPRETING GRAPHICS Use with Section % H 65.25% O 32.69% S 85.7% C 14.3% H Acid X Cyclohexane C 6 H % O 2.46% H 39.06% S 85.7% C 14.3% H Acid Y Use the circle graphs above to answer the following questions. 1. What is the percent of carbon in 50.0 g of cyclohexane? 2. Calculate the mass of hydrogen in g of ethene. Ethene C 2 H 4 3. Using the circle graphs, explain why percent composition alone is not sufficient to distinguish one compound from another. Chapter 10 Chemical Quantities 249

10 4. What information, in addition to percent composition, is needed to distinguish ethene from cyclohexane? 5. Scientists can use reactivity as a means of distinguishing between compounds with the same empirical formula. Ethene reacts with bromine to form dibromoethane, C 2 H 4 Br 2. Cyclohexane does not react with bromine. Create a circle graph to show the percent composition of dibromoethane. 6. Which of the circle graphs, labeled Acid X and Acid Y, represents the percentage composition of sulfuric acid, H 2 SO 4? Which represents the percentage composition of sulfurous acid, H 2 SO 3? 250 Core Teaching Resources

11 10 CHEMICAL QUANTITIES Vocabulary Review Select the term from the following list that best matches each description. mole Avogadro s number molar mass 22.4 L percent composition empirical formula standard temperature and pressure (0 C, 1 atm) 1. a description of the relative amounts of each element in a compound 2. the lowest whole-number ratio of the atoms of the elements in a compound 3. the volume occupied by one mole of any gas at STP 4. the mass (in grams) of one mole of a compound 5. the SI unit representing representative particles of a substance particles 7. the temperature and pressure at which one mole of gas occupies a volume of 22.4 L Chapter 10 Chemical Quantities 251

12 10 CHEMICAL QUANTITIES Chapter Quiz Fill in the word(s) that will make each statement true. 1. Counting, finding mass, and finding volume are all ways of 1. measuring the amount of The 2 is the mass, in amus, of one atom of a 2. monatomic element. 3. The 3 is the mass in grams of one mole of a substance The representative particle of most elements is the To convert moles of oxygen gas (O 2 ) to mass in grams, you can 5. use the conversion factor Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 6. The density of ethane gas, C 2 H 6, at STP is 1.34 g/l The volume of 3 moles of oxygen at STP is 67.2 L One mole of a gas occupies 22.4 L To convert a volume of 3.20 L of hydrogen gas to the number of moles, L you would use the conversion factor molh The density of a gas at STP can be used to calculate the molar mass 10.2 of that gas. Solve the following problems. Show your work in the space provided. 11. What mass of gold contains as many atoms as 3.05 g of silver? What is the empirical formula of a compound that is 40.7% carbon, 54.2% 10.3 oxygen, and 5.1% hydrogen? 252 Core Teaching Resources

13 10 CHEMICAL QUANTITIES Chapter Test A A. Matching Match each description in Column B to the correct term in Column A. Write the letter of the correct description on the line. Column A Column B standard temperature and pressure molar volume representative particle molar mass atomic mass Avogadro s number a. the volume occupied by a mole of any gas at STP (22.4 L) b. the mass in amus of an atom of an element c. the number of representative particles in a mole of a substance d. the percent by mass of each element in a compound e. the mass of a mole of a substance f. the formula that gives the lowest whole-number ratio of the elements in a compound mole (mol) empirical formula percent composition molar mass B. Multiple Choice Choose the best answer and write its letter on the line. g. an atom, a formula unit, or a molecule h. the mass in grams of a mole of any pure substance i representative particles of a substance j. 0 C and kpa 11. How many hydrogen atoms are in 4 molecules of isopropyl alcohol, C 3 H 8 O? a. 4 ( ) c. 32 b. 4 d. 32 ( ) 12. The mass of a mole of NaCl is its: a. molar mass. c. gram atomic mass. b. empirical formula. d. atomic mass. Chapter 10 Chemical Quantities 253

14 13. The chemical formula of aspirin is C 9 H 8 O 4. What is the mass of mol of aspirin? a g c. 80 g b. 5.4 g d g 14. How many moles of SO 3 are in molecules of SO 3? a c. 4.0 b d What is the volume (in liters at STP) of 2.50 mol of carbon monoxide? a L c L b L d L 16. The molar mass of molecular oxygen is: a. equal to the mass of one mole of oxygen atoms. b g. c g. d. none of the above 17. At STP, 1 mol each of hydrogen, oxygen, nitrogen, and fluorine: a. have different densities. b. occupy different volumes. c. are monatomic elements. d. contain twice Avogadro s number of representative particles. 18. A large weather balloon filled with helium has a volume of L at STP. Which expression should be used to find the mass of helium in the balloon? a m L ol 4 g He L/ m l m c. ol ol 2 4 g He mol b g L m He ol d L/ mol 4 g He l mol 19. The molar mass of a gas can be determined from: a. the density of the gas at STP. b. the volume of a mole of the gas. c. Avogadro s number. d. none of the above 20. What is the percent by mass of carbon in acetone, C 3 H 6 O? a. 1.60% c. 62% b. 30.0% d. 20.7% 21. Which of the following is not an empirical formula? a. Na 2 SO 4 c. N 2 H 4 b. C 6 H 5 Cl d. Sn 3 (PO 4 ) Which expression represents the percent by mass of nitrogen in NH 4 NO 3? a g 100 c g g g b g 100 d g g g 254 Core Teaching Resources

15 23. A compound has the empirical formula C 2 H 3 O and a molar mass of 172 g. What is its molecular formula? a. C 6 H 9 O 3 c. C 9 H 16 O 3 b. C 8 H 12 O 4 d. C 7 H 8 O The empirical formula of a compound is CH 2 F. The molar mass of this compound is 66.0 g. The molecular formula of the compound is: a. C 4 H 8 F 4. c. C 2 H 4 F 2. b. C 4 H 4 F 4. d. CH 2 F. C. Problems Solve the following problems in the space provided. Show your work. 25. Find the mass, in grams, of molecules of F The polymer used for the nonstick surface of cooking utensils is 24.0% C and 76.0% F by mass. What is the empirical formula of this polymer? 27. Find the number of moles of argon in 364 g of argon. D. Essay Write a short essay for the following. 28. The adjective molar in the phrase molar mass means of or pertaining to a mole. How does this definition support your understanding of molar mass as it is applied to atoms, molecules, ions, formula units, and other particles? Chapter 10 Chemical Quantities 255

16 10 CHEMICAL QUANTITIES Chapter Test B A. Matching Match each term in Column B with the correct description in Column A. Write the letter of the correct term on the line. Column A Column B the percent by mass of each element in a compound 0 C and kpa or 1 atmosphere a. molar mass b. empirical formula the lowest whole-number ratio of the atoms of elements in a compound the species present in a substance usually atoms, molecules, or formula units c. atomic mass d. molar volume representative particles of a substance the mass of an atom of an element the mass of one mole of any element or compound e. representative particle f. percent composition g. one mole L of any gas measured at STP B. Multiple Choice Choose the best answer and write its letter on the line. 9. How many oxygen atoms are in 10 formula units of Al 2 (SO 4 ) 3? a. 10 atoms O c. 70 atoms O b. 7 atoms O d. 120 atoms O 10. How many molecules are in 4.50 moles of H 2 O? a. 450 molecules c molecules b molecules d molecules 11. How many moles are in molecules of CO 2? a mol c mol b mol d mol h. standard temperature and pressure 256 Core Teaching Resources

17 12. What is the molar mass of C 3 H 8? a g c g b g d g 13. The representative particle for nitrogen is: a. an atom. c. a formula unit. b. a molecule. d. none of the above 14. What is the molar mass of MgCl 2? a g c g b g d g 15. How many grams are in 6.50 moles of H 2 SO 4? a. 638 g c g b g d g 16. Find the number of moles in 3.30 g of (NH 4 ) 2 SO 4? a mol c mol b mol d mol 17. What is the mass of moles of Fe 2 O 3? a g c b g d g 18. At STP, one mole of any gas occupies a volume of: a. 1 L. c L. b L. d. none of the above 19. What is the volume, in liters, of 3.75 moles of O 2 gas at STP? a L c L b L d L 20. Determine the number of moles in 625 L of H 2 gas at STP. a mol c mol b mol d mol 21. The density of a gaseous compound is g/l at STP. Determine the molar mass of the compound. a g c g b g d g 22. How many atoms are contained in 12.5 grams of silver? a atoms c atoms b atoms d atoms 23. What is the percent of aluminum in Al 2 (SO 4 ) 3? a. 28.1% c. 15.8% b. 54.0% d. 56.7% 24. What is the mass of hydrogen in 50.0 g of propane, C 3 H 8? a g c g b. 9.1 g d g Chapter 10 Chemical Quantities 257

18 25. What is the empirical formula of a compound that is 3.05% carbon, 0.26% hydrogen, and 96.69% iodine? a. C 2 HI 7 c. C 3 H 2 I 11 b. CH 2 I 5 d. CHI A compound has an empirical formula of C 3 H 5 O 2 and a molar mass of g. What is the molecular formula of this compound? a. C 6 H 5 O 4 c. C 6 H 10 O 4 b. C 9 H 15 O 6 d. C 12 H 20 O 8 C. Problems Solve the following problems in the space provided. Show your work. 27. How many atoms are contained in 0.25 moles of Fe? 28. Find the mass, in grams, of 6.25 mol H 2 SO What is the volume, in liters, of 15.0 kg of CO 2 at STP? 30. Determine the molar mass of a compound that has a density of g/l at STP. 31. What is the mass, in grams, of atoms of gold? 32. Calculate the percent composition of Mg(NO 3 ) Core Teaching Resources

19 33. What is the empirical formula of a compound that is 27.3% C and 72.7% O? 34. A compound consisting of 56.38% phosphorus and 43.62% oxygen has a molar mass of g/mol. Determine its molecular formula. D. Essay Write a short essay for the following. 35. Explain how the mass of a single atom in an element (in amu), the mass of one mole of atoms of that element, and Avogadro s number are related. Chapter 10 Chemical Quantities 259