CHEM 10113, Exam 1 September 19, 2006

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1 CHEM 10113, Exam 1 September 19, 2006 Name (please print) All answers must use the correct number of significant figures, and must show units! 1. (15 points) Mercury poisoning is a debilitating disease that can be fatal. If the amount of mercury in a polluted lake is 0.40 g Hg/mL, what is the total mass in kilograms of mercury in the lake? (The lake has a surface area of 125 mi 2 and an average depth of 22 ft.) Lake volume: (1 km) 2 = ( mi) 2, so 1 km 2 = mi 2 (1 km) 2 = (1000 m) 2, so 1 km 2 = 10 6 m 2 (1 m) 2 = (100 cm) 2, so 1 m 2 = 10 4 cm mi 2 lake x (1 km 2 )/( mi 2 ) x (10 6 m 2 )/(1 km 2 ) x (10 4 cm 2 )/(1 m 2 ) = x cm 2 22 feet deep x (12 in)/(1 ft) x (2.54 cm)/(1 in) = cm Lake volume = ( x )(670.56) = x cm 3 (note cm 3 = ml) Amount of Hg: x ml lake x (0.40 g Hg)/(1 ml lake) x (1 g Hg)/(10 6 g Hg) x (1 kg Hg)/(1000 g Hg) = 8.7 x 10 5 kg Hg 2. (10 points) In the following organic compounds, identify each of the boxed functional groups by writing the appropriate family name (i.e. ketone, alkene, etc) next to each box. (Each unlabeled corner is part of a carbon chain.)

2 3. (8 points) The isotope of an element, X, has a mass number of 79. The most stable ion of the isotope has 36 electrons and forms a binary compound with sodium having a formula of Na 2 X. Which of the following statements is/are true? For the false statements, correct them. a. The binary compound formed between X and fluorine will be a covalent compound. b. The isotope of X contains 38 protons. c. The isotope of X contains 41 neutrons. d. The identity of X is strontium, Sr. a. true b. F, x has 34 protons c. F, x has 45 neutrons d. F, x is selenium 4. (8 points) Balance the following equations. 16Ag (s) + S 8(s) 8Ag 2 S (s) 2Li (s) + 2H 2 O (l) 2LiOH (s) + H 2(g) 5. (12 points) SHOW ALL WORK. Protactinium (Pa), a highly toxic metal, is one of the rarest and most expensive elements. The following reaction is one method for its preparation: 2 PaI 5(s) 2 Pa (s) + 5 I 2(s) a) Given 15.8 mg of reactant, how many milligrams of protactinium could be synthesized? b) If 3.4 mg of Pa was actually obtained, what was the percent yield of this reaction? c) If you obtained 3.4 mg of Pa and the percent yield was 78.6%, how many grams of PaI 5 were used in the preparation? a) Pa= ; I = FW PaI 5 = g/mol Mol PaI 5 = g/ g/mol= x10-5 mol. Since ratio is 2:2 then mol number is the same, therefore: gpa= ( x 10-5 * )= 4.22 mg b) 4.22 mg % yield 3.4 mg % 81% c) 3.4 mg mg % mol of Pa=.00433g/ = x 10-5 mol Since ratio is 2:2 then g of PaI 5 = (1.8742x 10-5 * )= 16 mg

3 6. (15 points) Name the following compounds. Cr 2 (HPO 4 ) 3 BaO CS 2 XeF 4 HNO 2 chromium(iii) monohydrogen phosphate barium oxide carbon disulfide xenon tetrafluoride nitrous acid 7. (15 points) SHOW ALL WORK. In a quantitative analysis study, g of a compound containing carbon, hydrogen and oxygen only yielded 2.01 g of CO 2 and g of H 2 O in a combustion analysis apparatus. Determine the empirical formula of the compound. (MM CO 2 = 44.0 g/mol, MM H 2 O = g/mol) (2.01 g CO 2 ) x (1 mol CO 2 /44.0 g CO 2 ) x (1 mol C/1 mol CO 2 ) x ( g C/1 mol C) = g C (0.818 g H 2 O) x (1 mol H 2 O/18.0 g H 2 O) x (2 mol H/1 mol H 2 O) x (1.008 g H/1 mol H) = g H g g C g H = g O (0.549 g C) x (1 mol C/ g C) = mol C ( g H) x (1 mol H/1.008 g H) = mol H (0.181 g O) x (1 mol O/ g O) = mol O Divide through by to get C 4.04 H 8.04 O, round off to get C 4 H 8 O

4 9. (14 points) Match words from the following selection with the statements below. The same word may be used more than once, and not all words have to be used. There may be more than one word that matches each statement. strontium disulfur dichloride iodine germanium hafnium calcium rubidium oxide decomposition temperature volume strontium, iodine disulfur dichloride is from the same period as tin in the periodic table. is a molecular compound. decomposition temperature Is an example of an intensive property. germanium decomposition temperature is a metalloid. is an example of a chemical property. rubidium oxide disulfur dichloride strontium hafnium calcium is a binary compound. is expected to conduct electricity in the solid state. 9. (9 points) Briefly define the following terms. a.) hydrate: an ionic compound that crystallizes together with molecules of water in the crystal lattice b.) saturated solution: contains maximum amount of solute c.) potential energy: stored energy; can be converted to kinetic energy by movement

5 10. (8 points) SHOW ALL WORK. Phosphorus pentachloride reacts with water to give phosphoric acid and hydrogen chloride according to the the following equation: PCl 5(s) + 4 H 2 O (l) H 3 PO 4(l) + 5 HCl (g) In one experiment, mol of PCl 5 was slowly added to 2.06 mol of water. a) What reactant, if either, was the limiting reactant? b) How many grams of HCl were formed in the reaction? a) mol of PCl5 moles of PCl 5 = (2.06mol of H 2 O)(1 mol PCl 5 / 4 mol H 2 O) = mol Then PCl 5 is the limiting reactant b) grams of HCl= (.260 mol PCl 5 )* (5 Mol HCl/ 1 mol PCl 5 )( g/mol) = 47.4 g 11. (6 points) Complete the calculations, and report your answers using scientific notation, and the correct number of significant figures. a g g = x10 1 g b. (2.83 x 10 5 g) / (413.1 L) g/l = 7.41 x10 2 g/l 12. (18 points) Write chemical formulas for each of the following. propane sulfur dioxide hydrogen cyanide cobalt(iii) sulfide copper(i) sulfate pentahydrate chlorous acid C 3 H 8 SO 2 HCN Co 2 S 3 Cu 2 SO 4 5H 2 O HClO (3 points) The hallucinogenic drug LSD has the molecular formula C 20 H 25 N 3 O. One suspected sample contained 64.88% C, 5.95% H, and 9.46% N. What is the percentage O in the sample? %O = ( ) = 19.71%

6 14. (3 points) A certain hydrocarbon is composed entirely of C and H. In 4 mol of the compound there are 12 mol of C; in 6 molecules of the compound, there are 48 atoms of H. What is the empirical formula of the compound? 4 mol of CxHn has 12 mol C, therefore C=3. 6 molecules of CxHn have 48 atoms of H, therefore H=8. Empirical formula = C 3 H (3 points) Give the empirical formula of tetraarsenic decasulfide. As 2 S 5 CHEM 10113, Exam 1 September 19, 2006 Name (please print) All answers must use the correct number of significant figures, and must show units! 1. (15 points) Mercury poisoning is a debilitating disease that can be fatal. If the amount of mercury in a polluted lake is 0.52 g Hg/mL, what is the total mass in kilograms of mercury in the lake? (The lake has a surface area of 111 mi 2 and an average depth of 19 ft.) Lake volume: (1 km) 2 = ( mi) 2, so 1 km 2 = mi 2 (1 km) 2 = (1000 m) 2, so 1 km 2 = 10 6 m 2 (1 m) 2 = (100 cm) 2, so 1 m 2 = 10 4 cm mi 2 lake x (1 km 2 )/( mi 2 ) x (10 6 m 2 )/(1 km 2 ) x (10 4 cm 2 )/(1 m 2 ) = x cm 2 19 feet deep x (12 in)/(1 ft) x (2.54 cm)/(1 in) = cm Lake volume = ( x )(579.12) = x cm 3 (note cm 3 = ml) Amount of Hg: x ml lake x (0.52 g Hg)/(1 ml lake) x (1 g Hg)/(10 6 g Hg) x (1 kg Hg)/(1000 g Hg) = 8.7 x 10 5 kg Hg

7 2. (10 points) In the following organic compounds, identify each of the functional groups by writing the appropriate family name (i.e. ketone, alkene, etc) next to each box. Each unlabeled corner is part of a carbon chain. 3. (8 points) The isotope of an element, X, has a mass number of 79. The most stable ion of the isotope has 36 electrons and forms a binary compound with sodium having a formula of Na 2 X. Which of the following statements is/are true? For the false statements, correct them. a. The isotope of X contains 41 neutrons. b. The isotope of X contains 38 protons. c. The identity of X is strontium, Sr. d. The binary compound formed between X and fluorine will be a covalent compound. a. F, x has 45 neutrons b. F, x has 34 protons c. F, x is selenium d. true 4. (8 points) Balance the following equations. Na 2 CO 3 + Mg(NO 3 ) 2 MgCO NaNO 3 2 C 4 H 10 O O 2 8 CO H 2 O

8 5. (12 points) SHOW ALL WORK. Protactinium (Pa), a highly toxic metal, is one of the rarest and most expensive elements. The following reaction is one method for its preparation: 2 PaI 5(s) 2 Pa (s) + 5 I 2(s) a) Given 35.7 mg of reactant, how many milligrams of protactinium could be synthesized? b) If 7.2 mg of Pa was actually obtained, what was the percent yield of this reaction? c) If you obtained 7.2 mg of Pa and the percent yield was 82.5%, how many grams of PaI 5 were used in the preparation? a) Pa= ; I = FW PaI 5 = g/mol Mol PaI 5 = g/ g/mol= x10-5 mol. Since ratio is 2:2 then mol number is the same, therefore: gpa= ( x 10-5 * )= 9.53 mg b) 9.53 mg % yield 7.2 mg % 76% c) 7.2 mg mg % mol of Pa=.00873g/ = x 10-5 mol Since ratio is 2:2 then g of PaI 5 = (3.777x 10-5 * )= 33 mg 6. (15 points) Name the following compounds. SO 3 Na 2 SO 3 Mn 2 S 3 PI 3 HClO 2 sulfur trioxide sodium sulfate manganese(iii) sulfide phosphorus triiodide chlorous acid

9 7. (15 points) SHOW ALL WORK. In a quantitative analysis study, g of a compound containing carbon, hydrogen and oxygen only yielded g of CO 2 and g of H 2 O in a combustion analysis apparatus. Determine the empirical formula of the compound. (MM CO 2 = 44.0 g/mol, MM H 2 O = g/mol) (6.557 g CO 2 ) x (1 mol CO 2 /44.0 g CO 2 ) x (1 mol C/1 mol CO 2 ) x ( g C/1 mol C) = g C (4.026 g H 2 O) x (1 mol H 2 O/18.02 g H 2 O) x (2 mol H/1 mol H 2 O) x (1.008 g H/1 mol H) = g H g cmpd g C g H = g O ( g C) x (1 mol C/ g C) = mol C ( g H) x (1 mol H/1.008 g H) = mol H (2.384 g O) x (1 mol O/ g O) = mol O Divide through by to get CH 3 O.

10 8. (17 points) Match words from the following selection with the statements below. The same word may be used more than once, and not all words have to be used. All correct answers must be included to receive full credit! rubidium disulfur dichloride iron hafnium lead decomposition temperature volume polonium lithium oxide rubidium lithium oxide volume rubidium, iron, hafnium, lead is an element from the same period as tin. is an ionic compound. is an example of an extensive property. is a metal. volume is an example of a physical property. disulfur dichloride lithium oxide rubidium, iron, hafnium, lead is a binary compound. is expected to conduct electricity in the solid state. 9. (9 points) Briefly define the following terms. a.) kinetic energy: energy due to movement, dependent on mass and velocity b.) decanting: carefully pouring off c.) mass spectrometry: a method of measuring the masses of atoms and percent abundances of isotopes

11 10. (8 points) SHOW ALL WORK. Phosphorus pentachloride reacts with water to give phosphoric acid and hydrogen chloride according to the the following equation: PCl 5(s) + 4 H 2 O (l) H 3 PO 4(l) + 5 HCl (g) In one experiment, mol of PCl 5 was slowly added to 2.32 mol of water. a) What reactant, if either, was the limiting reactant? b) How many grams of HCl were formed in the reaction? a) mol of PCl5 moles of PCl 5 = (2.32mol of H 2 O)(1 mol PCl 5 / 4 mol H 2 O) = 0.58 mol Then PCl 5 is the limiting reactant b) grams of HCl= (.460 mol PCl 5 )* (5 mol HCl/ 1 mol PCl 5 )( g/mol) = 83.9 g 11. (6 points) Complete the calculations, and report your answers using scientific notation, and the correct number of significant figures. a) g g = 6.64 x10 0 g b) (1.43 x 10 5 g) / (43.2 L) g/l = 3.37 x10 3 g/l 12. (18 points) Write chemical formulas for each of the following. iron(iii) chloride hexahydrate barium phosphate butane tetraarsenic hexaoxide lead(iv) carbonate phosphoric acid FeCl 3 6H 2 O Ba 3 (PO 4 ) 2 C 4 H 10 As 4 O 6 Pb(CO 3 ) 2 H 3 PO (3 points) The hallucinogenic drug LSD has the molecular formula C 20 H 25 N 3 O. One suspected sample contained 72.07% C, 7.15% H, and 10.88% N. What is the percentage O in the sample? %O = ( ) = 9.90 %

12 14. (3 points) A certain hydrocarbon is composed entirely of C and H. In 4 mol of the compound there are 24 mol of C; in 6 molecules of the compound, there are 24 atoms of H. What is the empirical formula of the compound? 4 mol of CxHn has 24 mol C, therefore C=6. 6 molecules of CxHn have 24 atoms of H, therefore H=4. Molecular formula = C 6 H 4, so Empirical formula = C 3 H (3 points) Give the empirical formula of tetraarsenic decasulfide. As 2 S 5 CHEM 10113, Exam 1 September 19, 2006 Name (please print) All answers must use the correct number of significant figures, and must show units! 1. (15 points) Mercury poisoning is a debilitating disease that can be fatal. If the amount of mercury in a polluted lake is 0.35 g Hg/mL, what is the total mass in kilograms of mercury in the lake? (The lake has a surface area of 98 mi 2 and an average depth of 19 ft.) Lake volume: (1 km) 2 = ( mi) 2, so 1 km 2 = mi 2 (1 km) 2 = (1000 m) 2, so 1 km 2 = 10 6 m 2 (1 m) 2 = (100 cm) 2, so 1 m 2 = 10 4 cm 2 98 mi 2 lake x (1 km 2 )/( mi 2 ) x (10 6 m 2 )/(1 km 2 ) x (10 4 cm 2 )/(1 m 2 ) = x cm 2 19 feet deep x (12 in)/(1 ft) x (2.54 cm)/(1 in) = cm Lake volume = ( x )(579.12) = x cm 3 (note cm 3 = ml) Amount of Hg: x ml lake x (0.35 g Hg)/(1 ml lake) x (1 g Hg)/(10 6 g Hg) x (1 kg Hg)/(1000 g Hg) = 5.1 x 10 5 kg Hg

13 2. (10 points) In the following organic compounds, identify each of the functional groups by writing the appropriate family name (i.e. ketone, alkene, etc) next to each box. Each unlabeled corner is part of a carbon chain. 3. (8 points) The isotope of an element, X, has a mass number of 79. The most stable ion of the isotope has 36 electrons and forms a binary compound with sodium having a formula of Na 2 X. Which of the following statements is/are true? For the false statements, correct them. a. The isotope of X contains 38 protons. b. The isotope of X contains 41 neutrons. c. The identity of X is strontium, Sr. d. The binary compound formed between X and fluorine will be a covalent compound. a. F, x has 34 protons b. F, x has 45 neutrons c. F, x is selenium d. true 4. (8 points) Balance the following equations. H 3 PO 4(aq) + 3NaOH (aq) Na 3 PO 4(aq) + 3H 2 O (aq) N 2(g) + 3H 2(g) 2NH 3(g)

14 5. (12 points) SHOW ALL WORK. Protactinium (Pa), a highly toxic metal, is one of the rarest and most expensive elements. The following reaction is one method for its preparation: 2 PaI 5(s) 2 Pa (s) + 5 I 2(s) a) Given 12.1 mg of reactant, how many milligrams of protactinium could be synthesized? b) If 2.6 mg of Pa was actually obtained, what was the percent yield of this reaction? c) If you obtained 2.6 mg of Pa and the percent yield was 69.2%, how many grams of PaI 5 were used in the preparation? a) Pa= ; I = FW PaI 5 = g/mol Mol PaI 5 = g / g/mol= x10-5 mol. Since ratio is 2:2 then mol number is the same, therefore: gpa= ( x 10-5 * )= 3.23 mg b) 3.23 mg % yield 2.6 mg % 80% c) 2.6 mg mg % mol of Pa=.00376g/ = x 10-5 mol Since ratio is 2:2 then g of PaI 5 = (1.3275x 10-5 * )= 14 mg 6. (15 points) Name the following compounds. CuBr B 2 O 3 (NH 4 ) 3 P copper (I) bromide diboron trioxide ammonium phosphide SF 6 sulfur hexafluoride H 2 SO 3 sulfurous acid

15 7. (15 points) SHOW ALL WORK. In a quantitative analysis study, g of a compound containing carbon, hydrogen and oxygen only yielded g of CO 2 and g of H 2 O in a combustion analysis apparatus. Determine the empirical formula of the compound. (MM CO 2 = 44.0 g/mol, MM H 2 O = g/mol) (3.258 g CO 2 ) x (1 mol CO 2 /44.0 g CO 2 ) x (1 mol C/1 mol CO 2 ) x ( g C/1 mol C) = g C g H 2 O x (1 mol H 2 O/18.02 g H 2 O) x (2 mol H/1 mol H 2 O) x (1.008 g H/1mol H) = g H g g g = g O ( g C) x (1 mol C/ g C) = mol C ( g H) x (1 mol H/1.008 g H) = mol H ( g O) x (1 mol O/ g O) = mol O Divide through by to get C 1.5 H 4.0 O, multiply by two to get C 3 H 8 O 2

16 8. (17 points) Match words from the following selection with the statements below. The same word may be used more than once, and not all words have to be used. All correct answers must be included to receive full credit! rubidium disulfur dichloride lead iron hafnium decomposition temperature volume sulfur lithium oxide iron lithium oxide is an element from the same period as titanium. is an ionic compound. volume is an example of an extensive property. sulfur is a nonmetal. volume is an example of a physical property. disulfur dichloride lithium oxide Iron, rubidium, lead, hafnium is a binary compound. is expected to conduct electricity in the solid state. 9. (9 points) Briefly define the following terms. a) mass spectrometry: a method of measuring the masses of atoms and percent abundances of isotopes b) distillation : a process in which a mixture is heated to boil off the more volatile liquid c) solution: homogeneous mixture consisting of solvent (the bulk medium) and solute (the dissolved substance)

17 10. (8 points) SHOW ALL WORK. Phosphorus pentachloride reacts with water to give phosphoric acid and hydrogen chloride according to the the following equation: PCl 5(s) + 4 H 2 O (l) H 3 PO 4(l) + 5 HCl (g) In one experiment, mol of PCl 5 was slowly added to 2.00 mol of water. a) What reactant, if either, was the limiting reactant? b) How many grams of HCl were formed in the reaction? a) mol of PCl5 moles of PCl 5 = (2.00 mol of H 2 O)(1 mol PCl 5 / 4 mol H 2 O) = mol Then H 2 O is the limiting reactant b) grams of HCl= (2.00 mol H 2 O)* (5 Mol HCl/ 4 mol H 2 O)( g/mol) = 91.2 g 11. (6 points) Complete the calculations, and report your answers using scientific notation, and the correct number of significant figures. a) g g = x10 2 g b) (5.543 x 10 5 g) / (43.2 L) g/l = 1.28 x10 4 g/l 12. (18 points) Write chemical formulas for each of the following. mercury(i) dichromate potassium nitrate dinitrogen tetroxide calcium bromide dihydrate pentane acetic acid Hg 2 Cr 2 O 7 KNO 3 N 2 O 4 CaBr 2 2H 2 O C 5 H 12 HC 2 H 3 O (3 points) The hallucinogenic drug LSD has the molecular formula C 20 H 25 N 3 O. One suspected sample contained 74.07% C, 7.95% H, and 9.99% N. What is the percentage O in the sample? %O = ( ) = 7.99%

18 14. (3 points) A certain hydrocarbon is composed entirely of C and H. In 4 mol of the compound there are 16 mol of C; in 6 molecules of the compound, there are 24 atoms of H. What is the empirical formula of the compound? 4 mol of CxHn has 16 mol C, therefore C=4. 6 molecules of CxHn have 24 atoms of H, therefore H=6. Molecular formula = C 4 H 4, so Empirical formula = CH 15. (3 points) Give the empirical formula of dinitrogen tetroxide. NO 2