# Chapter 3 Mass Relations in Chemistry; Stoichiometry

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1 Chapter 3 Mass Relations in Chemistry; Stoichiometry MULTIPLE CHOICE 1. An atomic mass unit (amu) is defined as a C. b. the mass of 1 mole of hydrogen-s. c. the mass of 1 hydrogen-. d. the mass of 1 carbon-. e. 1/1 the mass of 1 carbon-.. Silver (107.7 amu) has two naturally occurring isotopes. In a typical sample, 51.4% of silver exists as Ag-107 ( amu). Calculate the atomic mass of the other isotope. a amu b amu c amu d amu e amu 3. Gallium has an atomic mass of 69.7 amu. In a typical sample, 60.4% of Ga exists as Ga-69 (6.957 amu). What is the identity and the atomic mass of the other isotope? 70 a. 30 Ga; 70.9 amu 70 b. 31 Ga; 70.9 amu 71 c. 31 Ga; 70.9 amu 71 d. 31 Ga; 71.9 amu 7 e. 31 Ga; 71.9 amu 4. An element has three naturally occurring isotopes with the following abundances and masses: abundance mass (amu) 7.99% % % Determine the atomic mass of the element. a amu b. 4.9 amu c amu d. 431 amu e. none of the above 1

2 5. The average molar mass of lithium is A sample of lithium consists of two isotopes with masses of amu and amu. Determine the percent abundance of each isotope. a. 7.49% Li-6 and 9.51% Li-7 b..45% Li-6 and 91.55% Li-7 c. 1.49% Li-6 and 7.51% Li-7 d % Li-6 and.45% Li-7 e. 9.51% Li-6 and 7.49% Li-7 6. Three naturally occurring isotopes of oxygen exist, O-16, O-17, and O-1. How many different O molecules are possible using these three isotopes? a. 3 b. 4 c. 5 d. 6 e Which one of the following is the most effective method of determining isotopic ratios of elements? a. distillation b. filtration c. chromatography d. absorption spectroscopy e. mass spectrometry. The molar mass of argon is g/mole. What is the mass of a single argon atom? a g b g c g d g e g 9. The molar mass of nitrogen (N ) is.0 g/mole. What is the mass of a single nitrogen atom? a g b g c g d g e g 10. The mass of a single molecule of elemental phosphorus is g. How many atoms combine to form a single molecule of elemental phosphorus? a. 1 b. c. 4 d. 6 e. 10

3 11. The mass of a single atom of zirconium is grams. Which is a correct method for determining the molar mass of Zr? 1 g a atoms moles 1 g atoms b atoms 1 mole g c moles g atoms d. 1 mole e. none of the above 1. The mass of a single atom of sulfur is grams. Which is a correct method for determining the molar mass of elemental sulfur, S? g S 1 mole S a mole mole S g S atoms mole S b. 1 mole S 1 mole S g S mole S c mole 1 mole S mole 1 mole S d g S mole S g S atoms 1 mole S e. 1 mole S mole S 13. A 1.45 g sample of chromium contains atoms. a b c d e

4 14. You have a 5.0 g sample of each of the following elements: Ra, Rb, Rh, Rn, Ru. Which sample contains the most atoms? a. Ra b. Rb c. Rh d. Rn e. Ru 15. Which of the following samples contains the largest number of atoms? a..0 moles of H 3 PO 4 b. 3.0 moles of H SO 3 c. 4.0 moles of HNO 3 d. 6.0 moles of HClO e..0 moles of HBr 16. Which of the following samples contains the largest number of hydrogen atoms? a..0 moles of C 6 H 16 b. 3.0 moles of C 3 H c. 4.0 moles of C 3 H 6 d. 6.0 moles of C H 4 e..0 moles of C H 17. What mass of oxygen is present in 10.0 grams of carbon dioxide (CO )? a. 0.7 g b g c g d. 7.7 g e..0 g 1. What is the mass in grams of 0.33 mol of glucose (C 6 H 1 O 6 )? a g b g c. 1. g d g e g 19. What is the mass in grams of 0.36 moles nitric acid (HNO 3 )? a g b g c.. g d. 53. g e. 174 g 4

5 0. Which is a correct method for determining the mass in grams of mol silver? a mol Ag g mol 1 g b mol Ag mole g c mol Ag mol 1 g d mol Ag mol e. none of the above 1. How many moles are present in 0.09 grams of HCl? a mol b mol c. 0. mol d. 3.6 mol e. 30 mol. Which is a correct method for calculating the moles present in 13 grams of calcium carbonate? atoms mol a. 13 g CaCO 3 1 mol 1 g 1 mol b. 13 g CaCO g g c. 13 g CaCO 3 1 mol mol d. 13 g CaCO 3 1 g e. none of the above 3. How many atoms are present in 5.00 grams of iron? a atoms b s c s d atoms e atoms 5

6 4. What is the total number of chlorine atoms present in.00 grams of magnesium chloride (MgCl )? a s b atoms c atoms d atoms e atoms 5. Which is a correct method for determining the total number of atoms in 13 grams of sulfur trioxide (SO 3 )? 1 mol a. 13 g SO g mol 1 mol atoms b. 13 g SO g 1 mol 1 mol 1 mol atoms atoms c. 13 g SO g 4 mol SO 3 1 mol 1 mol 4 mol atoms d. 13 g SO g 1 mol SO mol 1 mol 4 mol atoms atoms e. 13 g SO g 1 mol SO 3 1 mol 6. What mass of oxygen is present in 10.0 grams of potassium nitrate (KNO 3 )? a g b g c g d..00 g e g 7. What is the percent composition of silicon nitride (Si 3 N 4 )? a. 30.1% Si and 69.79% N b. 4.9% Si and 57.0% N c % Si and 45.97% N d % Si and 39.94% N e % Si and 30.60% N 6

7 . What is the percent composition of iron(ii) sulfate hexahydrate? a. 4.% Fe; 4.% S; 41.6% O; 50.0% H b. 16.7% Fe; 16.7%S; 66.6% O c. 1.5% Fe; 1.3%S; 4.6% O; 41.6% H d. 1.5% Fe; 1.3%S; 61.5% O; 4.7% H e. 36.% Fe; 1.1%S; 4.1% O 9. Which is a correct method for determining the mass of carbon present in 0.13 grams of propane (C 3 H )? 1 mol C 3 H 1.01 g C a g C 3 H g 1 mole 1 mol C 3 H 3 g C b g C 3 H g 1 mol C 3 H mol C 3 H 3 mol C 1.01 g C c g C 3 H 1 g 1 mol C 3 H 1 mole 1 mol C 3 H 1 mol C 1.01 g C d g C 3 H g 3 mol C 3 H 1 mole 1 mol C 3 H 3 mol C 1.01 g C e g C 3 H g 1 mol C 3 H 1 mole 30. Chalcopyrite is a mineral which contains 34.6% Cu, 30.43% Fe, and 34.95% S. What is the chemical formula for chalcopyrite? a. CuFeS b. CuFeS c. CuFe S d. Cu FeS e. Cu FeS 31. Beryl is a mineral which contains 5.03% Be, 10.04% Al, 31.35% Si, and 53.5% O. What is the chemical formula for beryl? a. BeAl(SiO 3 ) b. BeAl(SiO 3 ) 3 c. Be 3 (AlSiO 3 ) d. Be 3 Al (SiO 3 ) 6 e. Be 4 Al(SiO 3 ) 7

8 3. Which set of molecules is in order from lowest to highest mass percent oxygen? a. CH 3 < CH 3 CH < CH 3 CH CH < HOCH CH b. HOCH CH < CH 3 < CH 3 CH < CH 3 CH CH c. CH 3 CH CH < CH 3 CH < CH 3 < HOCH CH d. CH 3 CH < CH 3 CH CH < CH 3 < HOCH CH e. CH 3 CH < CH 3 < HOCH CH < CH 3 CH CH 33. Combustion analysis of.400 grams of toluene, an organic solvent, yields.03 g CO and 1.77 g H O. What is the simplest formula for toluene? a. C 7 H 4 b. C 4 H 7 c. C 7 H 6 d. C H 7 e. C 7 H 34. Isopentyl acetate, a molecule composed of C, H, and O, smells like bananas. Combustion analysis of grams of this molecule yields g H O and 4.14 g CO. What is the simplest formula for isopentyl acetate? a. C 7 H 14 O b. C 7 H 7 O 4 c. C H 10 O 3 d. C H 16 O e. C 9 H 6 O 35. Combustion analysis of 0.00 grams of an unknown hydrocarbon yields.613 g CO and 0.77 g H O. What is the percent composition of the hydrocarbon? a. 66.6% C; 33.4% H b..3% C; 17.7% H c. 9.1% C; 10.9% H d. 9.4% C; 7.60% H e. not enough information given to solve the problem 36. An oxide of nitrogen contains 63.1% oxygen and has a molar mass of 76.0 g/mol. What is the molecular formula for this compound? a. N O b. NO c. NO d. N O 3 e. N O 5

9 37. When propane undergoes complete combustion, the products are carbon dioxide and water. ac 3 H (g) + bo (g) cco (g) + dh O(g) What are the respective coefficients when the equation is balanced with the smallest whole numbers? a. a 1, b 1, c 1, d 1 b. a 1, b 1, c 3, d 4 c. a 1, b 3, c 3, d d. a 1, b 3, c 3, d 4 e. a 1, b 5, c 3, d 4 3. Hydrazine, a fuel used to power rocket engines, is a product of the reaction between ammonia and bleach. Balance the equation for the reaction. anh 3 (aq) + bocl - (aq) cn H 4 (l) + dcl - (aq) + eh O(l) a. a, b 1, c 1, d 1, e 1 b. a, b, c 1, d, e c. a, b 1, c, d 1, e d. a 4, b 3, c 1, d 3, e 1 e. a 4, b 3, c, d 3, e 39. The catalytic conversion of ammonia to nitric oxide is the first step in a three-step process which ultimately results in nitric acid. Balance the equation for the reaction. anh 3 (g) + bo (g) cno(g) + dh O(g) a. a, b 1, c, d 1 b. a 3, b, c 3, d 3 c. a 4, b 3, c, d 6 d. a 4, b 5, c 4, d 6 e. a 6, b 15, c 6, d The combustion of methanol, CH 3, yields carbon dioxide and water as products. Which of the reactions below is correct and properly balanced? a. CH 3 (l) + O (g) CO (g) + H O(g) b. CH 3 (l) + O (g) CO (g) + H O(g) c. CH 3 (l) + O (g) CO (g) + 4H O(g) d. CH 3 (l) + O (g) CO (g) + H O(g) e. CH 3 (l) + 3O (g) CO (g) + 4H O(g) 9

10 41. Aluminum reacts with oxygen to form aluminum oxide. Which of the reactions below is correct and properly balanced? a. Al(s) + O(g) AlO(s) b. Al(s) + O (g) AlO(s) c. 3Al(s) + O (g) Al 3 O (s) d. 4Al(s) + O (g) Al O(s) e. 4Al(s) + 3O (g) Al O 3 (s) 4. If 16.4 g of oxygen gas react with excess hydrogen, what mass of water is produced? H (g) + O (g) H O(g) a. 9.3 g b. 1.5 g c. 0.4 g d. 3.9 g e g 43. Which method is correct for determining the mass of carbon dioxide that can be made by the combustion of 3.19 grams of ethanol with excess oxygen? C (l) + 3O (g) CO (g) + 3H O(l) a g C 1 mole mole CO g CO g 1 mole C 1 mole b g C 1 mole 1 mole CO g CO g mole C 1 mole c g C 1 mole 1 mole CO g CO g 1 mole C 1 mole mole mole CO g CO d g C 1 g 1 mole C 1 mole mole 1 mole CO g CO e g C 1 g mole C 1 mole 10

11 44. How many moles of ammonia can be made by reacting 7.0 mol of N with 4.0 mol of H? N (g) + 3H (g) NH 3 (g) a..7 mol b. 4.0 mol c. 7.0 mol d. 11 mol e. 14 mol 45. Sodium metal and water react to form sodium hydroxide and hydrogen gas. What mass of Na will react with excess water to produce 15 g Na? Na(s) + H O(l) H (g) + Na(aq) a. 4.3 g b. 5.4 g c..6 g d. 11 g e. 6 g 46. What mass of oxygen will react with.64 g of magnesium? Mg(s) + O (g) MgO(s) a g b g c. 1.6 g d g e g 47. What mass of carbon dioxide can be made by reacting 1.56 grams of sodium bicarbonate with 0.67 grams of hydrochloric acid? NaHCO 3 (s) + H + (aq) CO (g) + H O(l) + Na + (aq) a..5 g b..9 g c g d. 0.9 g e g 11

12 4. What mass of silver iodide can be made by the reaction of 10.0 g of silver nitrate (AgNO 3 ) with 10.0 g of sodium iodide (NaI)? Ag + (aq) + I - (aq) AgI(s) a.. g b g c. 13. g d e. 0.0 g 49. A mass of.15 g C H 4 (g) reacts with excess oxygen. If 16. g CO (g) is collected, what is the percent yield of the reaction? C H 4 (g) + 3O (g) CO (g) + H O(g) a. 5.6% b. 31.7% c. 41.0% d. 57.1% e. 63.3% 50. A mass of 4.00 g of H (g) reacts with.00 g of O (g). If 1.94 g of H O(l) is collected, what is the percent yield of the reaction? H (g) + O (g) H O(l) a. 5.4 % b. 49 % c. 3 % d. 6 % e. 97 % 51. Hydrogen and nitrogen gases are reacted to produce kg of ammonia. If the percent yield of the reaction was only 15.%, what mass of hydrogen was initially present (assuming H (g) is the limiting reactant)? N (g) + 3H (g) NH 3 (g) a kg b kg c kg d kg e kg 1

13 grams of MgSO 4 H O, a hydrated salt with an unknown water content, is dried in an oven to remove the water. After drying, the anhydrous salt has a mass of 1.1 grams. How many moles of water are present per mole of hydrated magnesium sulfate? a. 1 b. 3 c. 5 d. 7 e Which of the balanced chemical equations is consistent with the following pictoral representation of a chemical reaction? a. SO + O SO 3 b. H + I HI c. H + O H O d. N + 3H NH 3 e. none of the above 13

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