Problem Solving Mole Concept

Back Print Lesson Name Class Date Skills Worksheet Problem Solving Mole Concept Suppose you want to carry out a reaction that requires combining one atom of iron with one atom of sulfur. How much iron should you use? How much sulfur? When you look around the lab, there is no device that can count numbers of atoms. Besides, the merest speck (0.001 g) of iron contains over a billion billion atoms. The same is true of sulfur. Fortunately, you do have a way to relate mass and numbers of atoms. One iron atom has a mass of 55.847 amu, and 55.847 g of iron contains 6.022 137  1023 atoms of iron. Likewise, 32.066 g of sulfur contains 6.022 137  1023 atoms of sulfur. Knowing this, you can measure out 55.847 g of iron and 32.066 g of sulfur and be pretty certain that you have the same number of atoms of each. The number 6.022 137  1023 is called Avogadro’s number. For most purposes it is rounded off to 6.022  1023. Because this is an awkward number to write over and over again, chemists refer to it as a mole (abbreviated mol). 6.022  1023 objects is called a mole, just as you call 12 objects a dozen. Look again at how these quantities are related. 55.847 g of iron  6.022  1023 iron atoms  1 mol of iron 32.066 g of sulfur  6.022  1023 sulfur atoms  1 mol of sulfur General Plan for Converting Mass, Amount, and Numbers of Particles 1 Mass of substance Convert using the molar mass of the substance. 2 Amount of substance in moles 3 Use Avogadro's number for conversion. Number of atoms, molecules, or formula units of substance Mole Concept Back Lesson Print Name Class Date Problem Solving continued PROBLEMS INVOLVING ATOMS AND ELEMENTS Sample Problem 1 A chemist has a jar containing 388.2 g of iron filings. How many moles of iron does the jar contain? Solution ANALYZE What is given in the problem? mass of iron in grams What are you asked to find? amount of iron in moles Items Data Mass of iron 388.2 g Molar mass of iron* 55.85 g/mol Amount of iron ? mol * determined from the periodic table PLAN What step is needed to convert from grams of Fe to number of moles of Fe? The molar mass of iron can be used to convert mass of iron to amount of iron in moles. 1 Mass of Fe in g multiply by the inverse molar mass of Fe 2 Amount of Fe in mol 1 molar mass Fe given g Fe  1 mol Fe  mol Fe 55.85 g Fe COMPUTE 388.2 g Fe  1 mol Fe  6.951 mol Fe 55.85 g Fe EVALUATE Are the units correct? Yes; the answer has the correct units of moles of Fe. Mole Concept Back Lesson Print Name Class Date Problem Solving continued Is the number of significant figures correct? Yes; the number of significant figures is correct because there are four significant figures in the given value of 388.2 g Fe. Is the answer reasonable? Yes; 388.2 g Fe is about seven times the molar mass. Therefore, the sample contains about 7 mol. Practice 1. Calculate the number of moles in each of the following masses: a. 64.1 g of aluminum ans: 2.38 mol Al b. 28.1 g of silicon ans: 1.00 mol Si c. 0.255 g of sulfur ans: 7.95  103 mol S d. 850.5 g of zinc ans: 13.01 mol Zn Mole Concept Back Lesson Print Name Class Date Problem Solving continued Sample Problem 2 A student needs 0.366 mol of zinc for a reaction. What mass of zinc in grams should the student obtain? Solution ANALYZE What is given in the problem? amount of zinc needed in moles What are you asked to find? mass of zinc in grams Items Data Amount of zinc 0.366 mol Molar mass of zinc 65.39 g/mol Mass of zinc ?g PLAN What step is needed to convert from moles of Zn to grams of Zn? The molar mass of zinc can be used to convert amount of zinc to mass of zinc. 2 1 Amount of Zn in mol Mass of Zn in mol multiply by the molar mass of Zn molar mass Zn given 65.39 g Zn mol Zn   g Zn 1 mol Zn COMPUTE 0.366 mol Zn  65.39 g Zn  23.9 g Zn 1 mol Zn EVALUATE Are the units correct? Yes; the answer has the correct units of grams of Zn. Is the number of significant figures correct? Yes; the number of significant figures is correct because there are three significant figures in the given value of 0.366 mol Zn. Is the answer reasonable? Yes; 0.366 mol is about 1/3 mol. 23.9 g is about 1/3 the molar mass of Zn. Mole Concept Back Lesson Print Name Class Date Problem Solving continued Practice 1. Calculate the mass of each of the following amounts: a. 1.22 mol sodium ans: 28.0 g Na b. 14.5 mol copper ans: 921 g Cu c. 0.275 mol mercury ans: 55.2 g Hg d. 9.37  103 mol magnesium ans: 0.228 Mg Mole Concept Back Print Lesson Name Class Date Problem Solving continued Sample Problem 3 How many moles of lithium are there in 1.204  1024 lithium atoms? Solution ANALYZE What is given in the problem? number of lithium atoms What are you asked to find? amount of lithium in moles Items Data Number of lithium atoms 1.204  1024 atoms Avogadro’s number—the number of atoms per mole 6.022  1023 atoms/mol Amount of lithium ? mol PLAN What step is needed to convert from number of atoms of Li to moles of Li? Avogadro’s number is the number of atoms per mole of lithium and can be used to calculate the number of moles from the number of atoms. 3 2 Number of Li atoms Amount of Li in mol multiply by the inverse of Avogadro's number 1 Avogadro's number given atoms Li  1 mol Li  mol Li 6.022  1023 atoms Li COMPUTE 1.204  1024 atoms Li  1 mol Li  1.999 mol Li 6.022  1023 atoms Li EVALUATE Are the units correct? Yes; the answer has the correct units of moles of Li. Is the number of significant figures correct? Yes; four significant figures is correct. Is the answer reasonable? Yes; 1.204  1024 is approximately twice Avogadro’s number. Therefore, it is reasonable that this number of atoms would equal about 2 mol. Mole Concept Back Lesson Print Name Class Date Problem Solving continued Practice 1. Calculate the amount in moles in each of the following quantities: a. 3.01  1023 atoms of rubidium ans: 0.500 mol Rb b. 8.08  1022 atoms of krypton ans: 0.134 mol Kr c. 5 700 000 000 atoms of lead ans: 9.5  1015 mol Pb d. 2.997  1025 atoms of vanadium ans: 49.77 mol V Mole Concept Back Lesson Print Name Class Date Problem Solving continued CONVERTING THE AMOUNT OF AN ELEMENT IN MOLES TO THE NUMBER OF ATOMS In Sample Problem 3, you were asked to determine the number of moles in 1.204  1024 atoms of lithium. Had you been given the amount in moles and asked to calculate the number of atoms, you would have simply multiplied by Avogadro’s number. Steps 2 and 3 of the plan for solving Sample Problem 3 would have been reversed. Practice 1. Calculate the number of atoms in each of the following amounts: a. 1.004 mol bismuth ans: 6.046  1023 atoms Bi b. 2.5 mol manganese ans: 1.5  1024 atoms Mg c. 0.000 000 2 mol helium ans: 1  1017 atoms He d. 32.6 mol strontium ans: 1.96  1025 atoms Sr Mole Concept Back Lesson Print Name Class Date Problem Solving continued Sample Problem 4 How many boron atoms are there in 2.00 g of boron? Solution ANALYZE What is given in the problem? mass of boron in grams What are you asked to find? number of boron atoms Items Data Mass of boron 2.00 g Molar mass of boron 10.81 g/mol Avogadro’s number—the number of boron atoms per mole of boron 6.022  1023 atoms/mol Number of boron atoms ? atoms PLAN What steps are needed to convert from grams of B to number of atoms of B? First, you must convert the mass of boron to moles of boron by using the molar mass of boron. Then you can use Avogadro’s number to convert amount in moles to number of atoms of boron. 1 3 Mass of B in g Number of B atoms multiply by the inverse of the molar mass of boron 2 multiply by Avogadro's number Amount of B in mol 1 molar mass B Avogadro's number 1 mol B 6.022  1023 atoms B gB   atoms B 10.81 g B 1 mol B given COMPUTE 2.00 g B  1 mol B 6.022  1023 atoms B   1.11  1023 atoms B 10.81 g B 1 mol B EVALUATE Are the units correct? Yes; the answer has the correct units of atoms of boron. Is the number of significant figures correct? Yes; the mass of boron was given to three significant figures. Mole Concept Back Lesson Print Name Class Date Problem Solving continued Is the answer reasonable? Yes; 2 g of boron is about 1/5 of the molar mass of boron. Therefore, 2.00 g boron will contain about 1/5 of an Avogadro’s constant of atoms. Practice 1. Calculate the number of atoms in each of the following masses: a. 54.0 g of aluminum ans: 1.21  1024 atoms Al b. 69.45 g of lanthanum ans: 3.011  1023 atoms La c. 0.697 g of gallium ans: 6.02  1021 atoms Ga d. 0.000 000 020 g beryllium ans: 1.3  1015 atoms Be Mole Concept Back Lesson Print Name Class Date Problem Solving continued CONVERTING NUMBER OF ATOMS OF AN ELEMENT TO MASS Sample Problem 4 uses the progression of steps 1 → 2 → 3 to convert from the mass of an element to the number of atoms. In order to calculate the mass from a given number of atoms, these steps will be reversed. The number of moles in the sample will be calculated. Then this value will be converted to the mass in grams. Practice 1. Calculate the mass of the following numbers of atoms: a. 6.022  1024 atoms of tantalum ans: 1810. g Ta b. 3.01  1021 atoms of cobalt ans: 0.295 g Co c. 1.506  1024 atoms of argon ans: 99.91 g Ar d. 1.20  1025 atoms of helium ans: 79.7 g He Mole Concept Back Lesson Print Name Class Date Problem Solving continued PROBLEMS INVOLVING MOLECULES, FORMULA UNITS, AND IONS How many water molecules are there in 200.0 g of water? What is the mass of 15.7 mol of nitrogen gas? Both of these substances consist of molecules, not single atoms. Look back at the diagram of the General Plan for Converting Mass, Amount, and Numbers of Particles. You can see that the same conversion methods can be used with molecular compounds and elements, such as CO2 , H2O, H2SO4 , and O2 . For example, 1 mol of water contains 6.022  1023 H2O molecules. The mass of a molecule of water is the sum of the masses of two hydrogen atoms and one oxygen atom, and is equal to 18.02 amu. Therefore, 1 mol of water has a mass of 18.02 g. In the same way, you can relate amount, mass, and number of formula units for ionic compounds, such as NaCl, CaBr2 , and Al2(SO4)3. Sample Problem 5 How many moles of carbon dioxide are in 66.0 g of dry ice, which is solid CO2? Solution ANALYZE What is given in the problem? mass of carbon dioxide What are you asked to find? amount of carbon dioxide Items Data Mass of CO2 66.0 g Molar mass of CO2 44.0 g/mol Amount of CO2 ? mol PLAN What step is needed to convert from grams of CO2 to moles of CO2? The molar mass of CO2 can be used to convert mass of CO2 to moles of CO2. 1 2 Mass of CO2 in g Amount of CO2 in mol multiply by the inverse of the molar mass of CO2 given g CO2  1 molar mass CO2 1 mol CO2  mol CO2 44.01 g CO2 COMPUTE 66.0 g CO2  1 mol CO2  1.50 mol CO2 44.01 g CO2 Mole Concept Back Lesson Print Name Class Date Problem Solving continued EVALUATE Are the units correct? Yes; the answer has the correct units of moles CO2. Is the number of significant figures correct? Yes; the number of significant figures is correct because the mass of CO2 was given to three significant figures. Is the answer reasonable? Yes; 66 g is about 3/2 the value of the molar mass of CO2. It is reasonable that the sample contains 3/2 (1.5) mol. Practice 1. Calculate the number of moles in each of the following masses: a. 3.00 g of boron tribromide, BBr3 ans: 0.0120 mol BBr3 b. 0.472 g of sodium fluoride, NaF ans: 0.0112 mol NaF c. 7.50  102 g of methanol, CH3OH ans: 23.4 mol CH3OH d. 50.0 g of calcium chlorate, Ca(ClO3)2 ans: 0.242 mol Ca(ClO3)2 Mole Concept Back Lesson Print Name Class Date Problem Solving continued CONVERTING MOLES OF A COMPOUND TO MASS Perhaps you have noticed that Sample Problems 1 and 5 are very much alike. In each case, you multiplied the mass by the inverse of the molar mass to calculate the number of moles. The only difference in the two problems is that iron is an element and CO2 is a compound containing a carbon atom and two oxygen atoms. In Sample Problem 2, you determined the mass of 1.366 mol of zinc. Suppose that you are now asked to determine the mass of 1.366 mol of the molecular compound ammonia, NH3. You can follow the same plan as you did in Sample Problem 2, but this time use the molar mass of ammonia. Practice 1. Determine the mass of each of the following amounts: a. 1.366 mol of NH3 ans: 23.28 g NH3 b. 0.120 mol of glucose, C6H12O6 ans: 21.6 g C6H12O6 c. 6.94 mol barium chloride, BaCl2 ans: 1.45  103 g or 1.45 kg BaCl2 d. 0.005 mol of propane, C3H8 ans: 0.2 g C3H8 61 Mole Concept Back Lesson Print Name Class Date Problem Solving continued Sample Problem 6 Determine the number of molecules in 0.0500 mol of hexane, C6H14 . Solution ANALYZE What is given in the problem? amount of hexane in moles What are you asked to find? number of molecules of hexane Items Data Amount of hexane 0.0500 mol Avogadro’s number—the number of molecules per mole of hexane 6.022  1023 molecules/mol Molecules of hexane ? molecules PLAN What step is needed to convert from moles of C6H14 to number of molecules of C6H14? Avogadro’s number is the number of molecules per mole of hexane and can be used to calculate the number of molecules from number of moles. 2 3 Amount of C6H14 in mol Number of C6H14 molecules multiply by Avogadro's number Avogadro's number 6.022  1023 molecules C6H14 mol C6H14   molecules C6H14 1 mol C6H14 given COMPUTE 0.0500 mol C6H14  6.022  1023 molecules C6H14  3.01  1022 molecules C6H14 1 mol C6H14 EVALUATE Are the units correct? Yes; the answer has the correct units of molecules of C6H14. Is the number of significant figures correct? Yes; three significant figures is correct. Is the answer reasonable? Yes; multiplying Avogadro’s number by 0.05 would yield a product that is a factor of 10 less with a value of 3  1022. Mole Concept Back Lesson Print Name Class Date Problem Solving continued Practice 1. Calculate the number of molecules in each of the following amounts: a. 4.99 mol of methane, CH4 ans: 3.00  1024 molecules CH4 b. 0.005 20 mol of nitrogen gas, N2 ans: 3.13  1021 molecules N2 c. 1.05 mol of phosphorus trichloride, PCl3 ans: 6.32  1023 molecules PCl3 d. 3.5  105 mol of vitamin C, ascorbic acid, C6H8O6 ans: 2.1  1019 molecules C6H8O6 Mole Concept Back Lesson Print Name Class Date Problem Solving continued USING FORMULA UNITS OF IONIC COMPOUNDS Ionic compounds do not exist as molecules. A crystal of sodium chloride, for example, consists of Na ions and Cl ions in a 1:1 ratio. Chemists refer to a combination of one Na ion and one Cl ion as one formula unit of NaCl. A mole of an ionic compound consists of 6.022  1023 formula units. The mass of one formula unit is called the formula mass. This mass is used in the same way atomic mass or molecular mass is used in calculations. Practice 1. Calculate the number of formula units in the following amounts: a. 1.25 mol of potassium bromide, KBr ans: 7.53  1023 formula units KBr b. 5.00 mol of magnesium chloride, MgCl2 ans: 3.01  1024 formula units MgCl2 c. 0.025 mol of sodium carbonate, Na2CO3 ans: 1.5  1022 formula units Na2CO3 d. 6.82  106 mol of lead(II) nitrate, Pb(NO3)2 ans: 4.11  1018 formula units Pb(NO3)2 Mole Concept Back Lesson Print Name Class Date Problem Solving continued CONVERTING NUMBER OF MOLECULES OR FORMULA UNITS TO AMOUNT IN MOLES In Sample Problem 3, you determined the amount in moles of the element lithium. Suppose that you are asked to determine the amount in moles of copper(II) hydroxide in 3.34  1034 formula units of Cu(OH)2. You can follow the same plan as you did in Sample Problem 3. Practice 1. Calculate the amount in moles of the following numbers of molecules or formula units: a. 3.34  1034 formula units of Cu(OH)2 ans: 5.55  1010 mol Cu(OH)2 b. 1.17  1016 molecules of H2S ans: 1.94  108 mol H2S c. 5.47  1021 formula units of nickel(II) sulfate, NiSO4 ans: 9.08  103 mol NiSO4 d. 7.66  1019 molecules of hydrogen peroxide, H2O2 ans: 1.27  104 mol H2O2 Mole Concept Back Print Lesson Name Class Date Problem Solving continued Sample Problem 7 What is the mass of a sample consisting of 1.00  1022 formula units of MgSO4? Solution ANALYZE What is given in the problem? number of magnesium sulfate formula units What are you asked to find? mass of magnesium sulfate in grams Items Data Number of formula units of magnesium sulfate 1.00  1022 formula units Avogadro’s number—the number of formula units of magnesium sulfate per mole 6.022  1023 formula units/mol Molar mass of magnesium sulfate 120.37 g/mol Mass of magnesium sulfate ?g PLAN What steps are needed to convert from formula units of MgSO4 to grams of MgSO4? First, you must convert the number of formula units of MgSO4 to amount of MgSO4 by using Avogadro’s number. Then you can use the molar mass of MgSO4 to convert amount in moles to mass of MgSO4. 3 1 Number of MgSO4 formula units Mass of MgSO4 in g multiply by the molar mass of MgSO4 multiply by the inverse of Avogadro's number 2 Amount of MgSO4 in mol 1 Avogadro's number given formula units MgSO4  1 mol MgSO4 6.022  1023 formula units MgSO4 molar mass MgSO4 120.37 g MgSO4   g MgSO4 1 mol MgSO4 Mole Concept Back Lesson Print Name Class Date Problem Solving continued COMPUTE 1.00  1022 formula units MgSO4  1 mol MgSO4 6.022  1023 formula units MgSO4  120.37 g MgSO4  2.00 g MgSO4 1 mol MgSO4 EVALUATE Are the units correct? Yes; the answer has the correct units of grams of MgSO4. Is the number of significant figures correct? Yes; the number of significant figures is correct because data were given to three significant figures. Is the answer reasonable? Yes; 2 g of MgSO4 is about 1/60 of the molar mass of MgSO4. Therefore, 2.00 g MgSO4 will contain about 1/60 of an Avogadro’s number of formula units. Practice 1. Calculate the mass of each of the following quantities: a. 2.41  1024 molecules of hydrogen, H2 ans: 8.08 g H2 b. 5.00  1021 formula units of aluminum hydroxide, Al(OH)3 ans: 0.648 g Al(OH)3 c. 8.25  1022 molecules of bromine pentafluoride, BrF5 ans: 24.0 g BrF5 d. 1.20  1023 formula units of sodium oxalate, Na2C2O4 ans: 26.7 g Na2C2O4 Mole Concept Back Lesson Print Name Class Date Problem Solving continued CONVERTING MOLECULES OR FORMULA UNITS OF A COMPOUND TO MASS In Sample Problem 4, you converted a given mass of boron to the number of boron atoms present in the sample. You can now apply the same method to convert mass of an ionic or molecular compound to numbers of molecules or formula units. Practice 1. Calculate the number of molecules or formula units in each of the following masses: a. 22.9 g of sodium sulfide, Na2S ans: 1.77  1023 formula units Na2S b. 0.272 g of nickel(II) nitrate, Ni(NO3)2 ans: 8.96  1020 formula units Ni(NO3)2 c. 260 mg of acrylonitrile, CH2CHCN ans: 3.0  1021 molecules CH2CHCN Mole Concept Back Lesson Print Name Class Date Problem Solving continued Additional Problems 1. Calculate the number of moles in each of the following masses: a. 0.039 g of palladium b. 8200 g of iron c. 0.0073 kg of tantalum d. 0.006 55 g of antimony e. 5.64 kg of barium f. 3.37  106 g of molybdenum 2. Calculate the mass in grams of each of the following amounts: a. 1.002 mol of chromium b. 550 mol of aluminum c. 4.08  108 mol of neon d. 7 mol of titanium e. 0.0086 mol of xenon f. 3.29  104 mol of lithium 3. Calculate the number of atoms in each of the following amounts: a. 17.0 mol of germanium b. 0.6144 mol of copper c. 3.02 mol of tin d. 2.0  106 mol of carbon e. 0.0019 mol of zirconium f. 3.227  1010 mol of potassium 4. Calculate the number of moles in each of the following quantities: a. 6.022  1024 atoms of cobalt b. 1.06  1023 atoms of tungsten c. 3.008  1019 atoms of silver d. 950 000 000 atoms of plutonium e. 4.61  1017 atoms of radon f. 8 trillion atoms of cerium 5. Calculate the number of atoms in each of the following masses: a. 0.0082 g of gold b. 812 g of molybdenum c. 2.00  102 mg of americium d. 10.09 kg of neon e. 0.705 mg of bismuth f. 37 g of uranium Mole Concept Back Lesson Print Name Class Date Problem Solving continued 6. Calculate the mass of each of the following: a. 8.22  1023 atoms of rubidium b. 4.05 Avogadro’s numbers of manganese atoms c. 9.96  1026 atoms of tellurium d. 0.000 025 Avogadro’s numbers of rhodium atoms e. 88 300 000 000 000 atoms of radium f. 2.94  1017 atoms of hafnium 7. Calculate the number of moles in each of the following masses: a. 45.0 g of acetic acid, CH3COOH b. 7.04 g of lead(II) nitrate, Pb(NO3)2 c. 5000 kg of iron(III) oxide, Fe2O3 d. 12.0 mg of ethylamine, C2H5NH2 e. 0.003 22 g of stearic acid, C17H35COOH f. 50.0 kg of ammonium sulfate, (NH4)2SO4 8. Calculate the mass of each of the following amounts: a. 3.00 mol of selenium oxybromide, SeOBr2 b. 488 mol of calcium carbonate, CaCO3 c. 0.0091 mol of retinoic acid, C20H28O2 d. 6.00  108 mol of nicotine, C10H14N2 e. 2.50 mol of strontium nitrate, Sr(NO3)2 f. 3.50  106 mol of uranium hexafluoride, UF6 9. Calculate the number of molecules or formula units in each of the following amounts: a. 4.27 mol of tungsten(VI) oxide, WO3 b. 0.003 00 mol of strontium nitrate, Sr(NO3)2 c. 72.5 mol of toluene, C6H5CH3 d. 5.11  107 mol of -tocopherol (vitamin E), C29H50O2 e. 1500 mol of hydrazine, N2H4 f. 0.989 mol of nitrobenzene C6H5NO2 10. Calculate the number of molecules or formula units in each of the following masses: a. 285 g of iron(III) phosphate, FePO4 b. 0.0084 g of C5H5N c. 85 mg of 2-methyl-1-propanol, (CH3)2CHCH2OH d. 4.6  104 g of mercury(II) acetate, Hg(C2H3O2)2 e. 0.0067 g of lithium carbonate, Li2CO3 Mole Concept Back Lesson Print Name Class Date Problem Solving continued 11. Calculate the mass of each of the following quantities: a. 8.39  1023 molecules of fluorine, F2 b. 6.82  1024 formula units of beryllium sulfate, BeSO4 c. 7.004  1026 molecules of chloroform, CHCl3 d. 31 billion formula units of chromium(III) formate, Cr(CHO2)3 e. 6.3  1018 molecules of nitric acid, HNO3 f. 8.37  1025 molecules of freon 114, C2Cl2F4 12. Precious metals are commonly measured in troy ounces. A troy ounce is equivalent to 31.1 g. How many moles are in a troy ounce of gold? How many moles are in a troy ounce of platinum? of silver? 13. A chemist needs 22.0 g of phenol, C6H5OH, for an experiment. How many moles of phenol is this? 14. A student needs 0.015 mol of iodine crystals, I2, for an experiment. What mass of iodine crystals should the student obtain? 15. The weight of a diamond is given in carats. One carat is equivalent to 200. mg. A pure diamond is made up entirely of carbon atoms. How many carbon atoms make up a 1.00 carat diamond? 16. 8.00 g of calcium chloride, CaCl2, is dissolved in 1.000 kg of water. a. How many moles of CaCl2 are in solution? How many moles of water are present? b. Assume that the ionic compound, CaCl2 , separates completely into Ca2 and Cl ions when it dissolves in water. How many moles of each ion are present in the solution? 17. How many moles are in each of the following masses? a. 453.6 g (1.000 pound) of sucrose (table sugar), C12H22O11 b. 1.000 pound of table salt, NaCl 18. When the ionic compound NH4Cl dissolves in water, it breaks into one ammo nium ion, NH  4 , and one chloride ion, Cl . If you dissolved 10.7 g of NH4Cl in water, how many moles of ions would be in solution? 19. What is the total amount in moles of atoms in a jar that contains 2.41  1024 atoms of chromium, 1.51  1023 atoms of nickel, and 3.01  1023 atoms of copper? 20. The density of liquid water is 0.997 g/mL at 25°C. a. Calculate the mass of 250.0 mL (about a cupful) of water. b. How many moles of water are in 250.0 mL of water? Hint: Use the result of (a). c. Calculate the volume that would be occupied by 2.000 mol of water at 25°C. d. What mass of water is 2.000 mol of water? Mole Concept Back Lesson Print Name Class Date Problem Solving continued 21. An Avogadro’s number (1 mol) of sugar molecules has a mass of 342 g, but an Avogadro’s number (1 mol) of water molecules has a mass of only 18 g. Explain why there is such a difference between the mass of 1 mol of sugar and the mass of 1 mol of water. 22. Calculate the mass of aluminum that would have the same number of atoms as 6.35 g of cadmium. 23. A chemist weighs a steel cylinder of compressed oxygen, O2 , and finds that it has a mass of 1027.8 g. After some of the oxygen is used in an experiment, the cylinder has a mass of 1023.2 g. How many moles of oxygen gas are used in the experiment? 24. Suppose that you could decompose 0.250 mol of Ag2S into its elements. a. How many moles of silver would you have? How many moles of sulfur would you have? b. How many moles of Ag2S are there in 38.8 g of Ag2S? How many moles of silver and sulfur would be produced from this amount of Ag2S? c. Calculate the masses of silver and sulfur produced in (b). Mole Concept Back Lesson Print c. 60.4 kg; 1.88  104 dm3 d. 0.94 g/cm3; 5.3  104 m3 e. 2.5  103 kg; 2.7  106 cm3 7. 2.8 g/cm3 8. a. 0.72 m b. 2.5  103 atoms 9. 1300 L/min 10. 1.3  106 cal/h 11. 5.44 g/ cm3 12. 2.24  104 cm3 13. 32 000 uses 14. 2500 L 15. 9.5 L/min MOLE CONCEPT 1. a. b. c. d. e. f. 2. a. b. c. d. e. f. 3. a. b. c. d. e. f. 4. a. b. c. d. e. f. 5. a. b. c. d. e. f. 6. a. b. c. d. e. f. 7. a. b. 3.7  104 mol Pd 150 mol Fe 0.040 mol Ta 5.38  105 mol Sb 41.1 mol Ba 3.51  108 mol Mo 52.10 g Cr 1.5  104 g or 15 kg Al 8.23  107 g Ne 3  102 g or 0.3 kg Ti 1.1 g Xe 2.28  105 g or 228 kg Li 1.02  1025 atoms Ge 3.700  1023 atoms Cu 1.82  1024 atoms Sn 1.2  1030 atoms C 1.1  1021 atoms Zr 1.943  1014 atoms K 10.00 mol Co 0.176 mol W 4.995  105 mol Ag 1.6  1015 mol Pu 7.66  107 mol Rn 1  1011 mol Ce 2.5  1019 atoms Au 5.10  1024 atoms Mo 4.96  1020 atoms Am 3.011  1026 atoms Ne 2.03  1018 atoms Bi 9.4  1016 atoms U 117 g Rb 223 g Mn 2.11  105 g Te 2.6  103 g Rh 3.31  108 g Ra 8.71  105 g Hf 0.749 mol CH3COOH 0.0213 mol Pb(NO3)2 Holt Chemistry 3  104 mol Fe2O3 2.66  104 mol C2H5NH2 1.13  105 mol C17H35COOH 378 mol (NH4)2SO4 764 g SeOBr2 4.88  104 g CaCO3 2.7 g C20H28O2 9.74  106 g C10H14N2 529 g Sr(NO3)2 1.23  103 g UF6 2.57  1024 formula units WO3 1.81  1021 formula units Sr(NO3)2 4.37  1025 molecules C6H5CH3 3.08  1017 molecules C29H50O2 9.0  1026 molecules N2H4 5.96  1023 molecules C6H5NO2 1.14  1024 formula units FePO4 6.4  1019 molecules C5H5N 6.9  1020 molecules (CH3)2CHCH2OH d. 8.7  1017 formula units Hg(C2H3O2)2 e. 5.5  1019 formula units Li2CO3 a. 52.9 g F2 b. 1.19  103 g or 1.19 kg BeSO4 c. 1.388  105 g or 138.8 kg CHCl3 d. 9.6  1012 g Cr(CHO2)3 e. 6.6  104 g HNO3 f. 2.38  104 g or 23.8 kg C2Cl2F4 0.158 mol Au 0.159 mol Pt 0.288 mol Ag 13.0.234 mol C6H5OH 3.8 g I2 1.00  1022 atoms C a. 0.0721 mol CaCl2 55.49 mol H2O b. 0.0721 mol Ca2 0.144 mol Cl a. 1.325 mol C12H22O11 b. 7.762 mol NaCl 0.400 mol ions 4.75 mol atoms a. 249 g H2O b. 13.8 mol H2O c. 36.1 mL H2O d. 36.0 g H2O The mass of a sugar molecule is much greater than the mass of a water molecule. Therefore, the mass of 1 mol of sugar molecules is much greater than the mass of 1 mol of water molecules. 1.52 g Al c. d. e. f. 8. a. b. c. d. e. f. 9. a. b. c. d. e. f. 10. a. b. c. 11. 12. 14. 15. 16. 17. 18. 19. 20. 21. 22. 324 Answer Key Back Lesson Print 23. 0.14 mol O2 24. a. 0.500 mol Ag 0.250 mol S b. 0.157 mol Ag2S 0.313 mol Ag 0.157 mol S c. 33.8 g Ag 5.03 g S PERCENTAGE COMPOSITION 1. a. HNO3 b. c. d. 2. a. b. c. d. e. f. g. h. 3. a. b. c. 1.60% H 22.23% N 76.17% O NH3 82.22% N 17.78% H HgSO4 67.616% Hg 10.81% S 21.57% O SbF5 56.173% Sb 43.83% F 7.99% Li 92.01% Br 94.33% C 5.67% H 35.00% N 5.05% H 59.96% O 2.15% H 29.80% N 68.06% O 87.059% Ag 12.94% S 32.47% Fe 13.96% C 16.29% N 37.28% S LiC2H3O2 10.52% Li 36.40% C 4.59% H 48.49% O Ni(CHO2)2 39.46% Ni 16.15% C 1.36% H 43.03% O 46.65% N 23.76% S 89.491% Tl d. e. f. 4. a. b. c. d. e. f. 5. a. b. c. d. 6. a. 7. 8. 9. 10. 11. 12. 13. 14. 39.17% O 79.95% Br in CaBr2 78.767% Sn in SnO2 1.47 g O 26.5 metric tons Al 262 g Ag 0.487 g Au 312 g Se 3.1  104 g Cl 40.55% H2O 43.86% H2O 20.70% H2O 28.90% H2O Ni(C2H3O2)24H2O 23.58% Ni b. Na2CrO44H2O 22.22% Cr c. Ce(SO4)24H2O 34.65% Ce 43.1 kg Hg malachite: 5.75  102 kg Cu chalcopyrite: 3.46  102 kg Cu malachite has a greater Cu content a. 25.59% V b. 39.71% Sn c. 22.22% Cl 319.6 g anhydrous CuSO4 1.57 g AgNO3 54.3 g Ag 8.08 g S 23.1 g MgSO47H2O 3.27  102 g S EMPIRICAL FORMULAS 1. a. b. c. d. e. f. 2. a. b. c. 3. a. b. c. d. 4. a. b. c. d. e. f. BaCl2 BiO3H3 or Bi(OH)3 AlN3O9 or Al(NO3)3 ZnC4H6O4 or Zn(CH3COO)2 NiN2S2H8O8 or Ni(NH4)2SO4 C2HBr3O2 or CBr3COOH CuF2 Ba(CN)2 MnSO4 NiI2 MgN2O6 or Mg(NO3)2 MgS2O3, magnesium thiosulfate K2SnO3, potassium stannate As2S3 Re2O7 N2H4O3 or NH4NO3 Fe2Cr3O12 or Fe2(CrO4)3 C5H9N3 C6H5F2N or C6H3F2NH2 Answer Key