CHEM Exam 2 October 12, Version A

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1 CHEM Exam 2 October 12, Version A Constants and Conversion Factors Avogadro's Number: NA = 6.02x10 23 mol -1 Molar Masses: C O Al HCl AlCl CO2-44. NaCl AlF3-84. H3PO4-98. O

2 CHEM Exam 2 October 12, Version A (76) MULTIPLE CHOICE (Circle the ONE correct answer) Name NOTE: Required Molar Masses and non-metric conversion factors are given on the cover sheet. For #1 - #4: Consider the reaction: 2 Al + 6 HCl 2 AlCl3 + 3 H2. 1. What is the theoretical yield of AlCl3 when grams of HCl are reacted with an excess of Al? (A) 61 g (B) 223 g (C) 668 g (D) 178 g 2. When 135 grams of Al are reacted with 219 grams of HCl, what is the theoretical yield of AlCl3? (A) 148 g (B) 186 g (C) 668 g (D) 267 g 3. When 135 grams of Al are reacted with 219 grams of HCl, grams of remain when the reaction is complete. (A) 81 g, Al (B) 32 g, HCl (C) 54 g, Al (D) 81 g, HCl 4. When 292 grams of HCl reacts with an excess of Al, 125 grams of AlCl3 are formed. The percent yield is: (A) 26% (B) 49% (C) 35% (D) 12% 5. Consider the reaction, Fe(s) + O2(g) Fe2O3(s). Approximately how many moles of O2, reacting with excess Fe, are required to produce 5.0 moles of Fe2O3 if the percent yield for the reaction is 35%? (A) 21.4 mol (B) 2.6 mol (C) 9.5 mol (D) 17.1 mol 6. Consider the reaction, N2 + O2 N2O5. When 3.0 mol of N2 is reacted with 9.0 mol of O2, 1.80 mol of N2O5 is formed. The percent yield for this reaction is approximately: (A) 50% (B) 60% (C) 63% (D) 75% 7. Consider a hypothetical metal oxide, XxOy [M(X) = 70]. When 55. grams of XxOy are heated to drive off the oxygen, it is found that 35. grams of the solid metal (X) remains. What is the empirical formula of this compound? (A) XO2 (B) X2O3 (C) XO4 (D) X2O5

3 Version A 8. Consider the thermal decomposition of an unknown metal carbonate, XCO3(s): XCO () s XO() s + CO ( g) Heat 3 2 When 70. grams of XCO3 is decomposed, 22. grams of CO2 (M=44) are produced. What is the Molar Mass of the unknown metal; i.e. what is M(X)? (A) 80. g/mol (B) 55.5 g/mol (C) 140. g/mol (D) Cannot be determined without knowing the mass of XO produced For #9: The relevant solubility rules are: (a) All compounds containing Br - are soluble except AgBr, Hg2Br2, PbBr2, and (b) All compounds containing PO4 3- are insoluble except those containing NH4 + and Group 1A metal ions. 9. The Spectator Ions for the reaction of CaBr2(aq) and K3PO4(aq) are: (A) Ca 2+ and PO4 3- (B) Ca 2+ and Br - (C) K + and Br - (D) Br - and PO Which of the following solutions has the highest total concentration of ions? (A) 0.14 M Al(NO3)3 (C) 0.25 M KCl (B) 0.20 M Na2SO4 (D) 0.11 M Ba3(PO4)2 11. How many ml of 0.4 M NaCl can be prepared using 10. grams of NaCl? (A) 680 ml (B) 0.43 ml (C) 2340 ml (D) 430 ml 12. How many ml of water must be added to 150 ml 0.60 M HCl to decrease the concentration to 0.25 M? (A) 210 ml (B) 184 ml (C) 63 ml (D) 360 ml 13. If one mixes 400 ml of 0.40 M Sucrose with 300 ml of 0.60 M Sucrose, approximately how many additional ml of pure water must be added to the solution to have a final concentration of 0.25 M Sucrose? (A) 480 ml (B) 660 ml (C) 1360 ml (D) None of the above 14. Aluminum Fluoride, AlF3, is a sparingly soluble salt with a solubility of 0.72 g/100 ml of H2O at 25 o C. If you stir 9.40 grams of Ag2SO4 into 800. ml of water at 25 o C, what will be the approximate Molar concentration of Fluoride ions, [F - ], in the solution after it has come to equilibrium? (A) 0.14 M (B) 0.42 M (C) 0.26 M (D) M

4 Version A ml of 0.20 H3PO4(aq) is required to completely neutralize 300 ml of an aqueous Ba(OH)2(aq) solution. What is the Molarity of the Ba(OH)2(aq) solution? (A) 0.60 M (B) 0.40 M (C) 0.27 M (D) 0.20 M 16. You are given 6. grams of an unknown diprotic acid, H2A, which is completely neutralized by reaction with 400 ml of 0.20 M NaOH. The Molar Mass of the acid is approximately: (A) 37 g/mol (B) 75 g/mol (C) 103 g/mol (D) 150 g/mol 17. Regarding the reaction, Br2O5(s) + 5 CO(g) Br2(s) + 5 CO2(g), which of the following statements is/are true? (1) Br2O5 is the oxidizing agent (2) Br2 is oxidized (3) CO is oxidized (4) Br2O5 is reduced (A) 1 & 2 (B) 1 & 3 & 4 (C) 1 & 4 (D) All four statements For #18-#19: Consider the reaction: H3AsO4(aq) + Sr(OH)2(aq) Sr3(AsO4)2(s) + H2O(l). Consider when 700 ml of 0.40 M H3AsO4(aq) are mixed with 600 ml of 0.60 M Sr(OH)2). 18. What is the theoretical yield of Sr3(AsO4)2(s) in moles? (A) 0.12 mol (B) mol (C) 0.14 mol (C) 0.17 mol 19. At the conclusion of the reaction, remains and its Molar concentration is. (A) Sr(OH)2, M (C) Sr(OH)2, M (B) H3AsO4, M (D) H3AsO4, M Two (2) Problems follow (You MUST show your work to receive credit)

5 Version A (12) 1. A hypothetical metal carbonyl has the formula, Mx(CO)y. The Molar Mass of the metal is 140. g/mol. When a sample of this compound is burned in oxygen, 375. grams of the metal oxide, M2O3 and 352 grams of CO2 are formed. Note: M(M) = 140, M(M2O3) = 2(140) + 3(16) = 328 g/mol, M(CO2) = 44 g/mol. Determine the empirical formula of Mx(CO)y (12) 2. Assume that 6.0 grams of impure H3PO4 is dissolved in a convenient amount of water (the actual amount doesn't affect the calculation). When the above solution is titrated with 0.35 M NaOH(aq), it is found that 460. ml of the NaOH(aq) solution is required to completely neutralize the acid. Calculate the percent impurity in the NaOH sample.

6 CHEM Exam 2 October 12, Version B Constants and Conversion Factors Avogadro's Number: NA = 6.02x10 23 mol -1 Molar Masses: C O Al HCl AlCl CO2-44. NaCl AlF3-84. H3PO4-98. O

7 CHEM Exam 2 October 12, Version B (76) MULTIPLE CHOICE (Circle the ONE correct answer) Name NOTE: Required Molar Masses and non-metric conversion factors are given on the cover sheet. 1. Consider the reaction, N2 + O2 N2O5. When 3.0 mol of N2 is reacted with 9.0 mol of O2, 1.80 mol of N2O5 is formed. The percent yield for this reaction is approximately: (A) 50% (B) 63% (C) 60% (D) 75% 2. Consider the reaction, Fe(s) + O2(g) Fe2O3(s). Approximately how many moles of O2, reacting with excess Fe, are required to produce 5.0 moles of Fe2O3 if the percent yield for the reaction is 35%? (A) 17.1 mol (B) 2.6 mol (C) 9.5 mol (D) 21.4 mol For #3 - #6: Consider the reaction: 2 Al + 6 HCl 2 AlCl3 + 3 H2. 3. When 135 grams of Al are reacted with 219 grams of HCl, what is the theoretical yield of AlCl3? (A) 267 g (B) 186 g (C) 668 g (D) 148 g 4. When 135 grams of Al are reacted with 219 grams of HCl, grams of remain when the reaction is complete. (A) 32 g, HCl (B) 81 g, Al (C) 54 g, Al (D) 81 g, HCl 5. What is the theoretical yield of AlCl3 when grams of HCl are reacted with an excess of Al? (A) 61 g (B) 178 g (C) 668 g (D) 223 g 6. When 292 grams of HCl reacts with an excess of Al, 125 grams of AlCl3 are formed. The percent yield is: (A) 26% (B) 35% (C) 49% (D) 12% 7. Consider a hypothetical metal oxide, XxOy [M(X) = 70]. When 55. grams of XxOy are heated to drive off the oxygen, it is found that 35. grams of the solid metal (X) remains. What is the empirical formula of this compound? (A) XO2 (B) X2O3 (C) X2O5 (D) XO4

8 Version B For #8: The relevant solubility rules are: (a) All compounds containing Br - are soluble except AgBr, Hg2Br2, PbBr2, and (b) All compounds containing PO4 3- are insoluble except those containing NH4 + and Group 1A metal ions. 8. The Spectator Ions for the reaction of CaBr2(aq) and K3PO4(aq) are: (A) Ca 2+ and PO4 3- (B) K + and Br - (C) Ca 2+ and Br - (D) Br - and PO Consider the thermal decomposition of an unknown metal carbonate, XCO3(s): XCO () s XO() s + CO ( g) Heat 3 2 When 70. grams of XCO3 is decomposed, 22. grams of CO2 (M=44) are produced. What is the Molar Mass of the unknown metal; i.e. what is M(X)? (A) 55.5 g/mol (B) 80. g/mol (C) 140. g/mol (D) Cannot be determined without knowing the mass of XO produced 10. How many ml of 0.4 M NaCl can be prepared using 10. grams of NaCl? (A) 680 ml (B) 0.43 ml (C) 430 ml (D) 2340 ml 11. How many ml of water must be added to 150 ml 0.60 M HCl to decrease the concentration to 0.25 M? (A) 210 ml (B) 184 ml (C) 63 ml (D) 360 ml 12. Which of the following solutions has the highest total concentration of ions? (A) 0.14 M Al(NO3)3 (C) 0.25 M KCl (B) 0.11 M Ba3(PO4)2 (D) 0.20 M Na2SO4 13. Aluminum Fluoride, AlF3, is a sparingly soluble salt with a solubility of 0.72 g/100 ml of H2O at 25 o C. If you stir 9.40 grams of Ag2SO4 into 800. ml of water at 25 o C, what will be the approximate Molar concentration of Fluoride ions, [F - ], in the solution after it has come to equilibrium? (A) M (B) 0.42 M (C) 0.26 M (D) 0.14 M ml of 0.20 H3PO4(aq) is required to completely neutralize 300 ml of an aqueous Ba(OH)2(aq) solution. What is the Molarity of the Ba(OH)2(aq) solution? (A) 0.27 M (B) 0.40 M (C) 0.60 M (D) 0.20 M

9 Version B 15. If one mixes 400 ml of 0.40 M Sucrose with 300 ml of 0.60 M Sucrose, approximately how many additional ml of pure water must be added to the solution to have a final concentration of 0.25 M Sucrose? (A) 480 ml (B) 1360 ml (C) 660 ml (D) None of the above For #16-#17: Consider the reaction: H3AsO4(aq) + Sr(OH)2(aq) Sr3(AsO4)2(s) + H2O(l). Consider when 700 ml of 0.40 M H3AsO4(aq) are mixed with 600 ml of 0.60 M Sr(OH)2). 16. What is the theoretical yield of Sr3(AsO4)2(s) in moles? (A) 0.14 mol (B) mol (C) 0.12 mol (C) 0.17 mol 17. At the conclusion of the reaction, remains and its Molar concentration is. (A) Sr(OH)2, M (C) Sr(OH)2, M (B) H3AsO4, M (D) H3AsO4, M 18. Regarding the reaction, Br2O5(s) + 5 CO(g) Br2(s) + 5 CO2(g), which of the following statements is/are true? (1) Br2O5 is the oxidizing agent (2) Br2 is oxidized (3) CO is oxidized (4) Br2O5 is reduced (A) 1 & 2 (B) 1 & 3 & 4 (C) 1 & 4 (D) All four statements 19. You are given 6. grams of an unknown diprotic acid, H2A, which is completely neutralized by reaction with 400 ml of 0.20 M NaOH. The Molar Mass of the acid is approximately: (A) 150 g/mol (B) 75 g/mol (C) 103 g/mol (D) 37 g/mol Two (2) Problems follow (You MUST show your work to receive credit)

10 Version B (12) 1. A hypothetical metal carbonyl has the formula, Mx(CO)y. The Molar Mass of the metal is 140. g/mol. When a sample of this compound is burned in oxygen, 375. grams of the metal oxide, M2O3 and 352 grams of CO2 are formed. Note: M(M) = 140, M(M2O3) = 2(140) + 3(16) = 328 g/mol, M(CO2) = 44 g/mol Determine the empirical formula of Mx(CO)y. (12) 2. Assume that 6.0 grams of impure H3PO4 is dissolved in a convenient amount of water (the actual amount doesn't affect the calculation). When the above solution is titrated with 0.35 M NaOH(aq), it is found that 460. ml of the NaOH(aq) solution is required to completely neutralize the acid. Calculate the percent impurity in the NaOH sample.

CHEM 1413 Chapter 4 Homework Questions TEXTBOOK HOMEWORK

CHEM 1413 Chapter 4 Homework Questions TEXTBOOK HOMEWORK Chapter 3 3.68 Calculate each of the following quantities: (a) Mass (g) of solute in 185.8 ml of 0.267 M calcium acetate (b) Molarity of 500. ml