CHM 1310 FS04 EXAM 4 0800 T/TH Name: Ganley Date: Word Problem (20 points): n-caproic acid is a monoprotic acid containing only carbon, hydrogen, and oxygen. It is found in milk fats, coconut oil, and various palm and other oils. In spite of it's characteristic goat-like odor, it is used in the food industry for the manufacture of chemicals for artificial flavors. Caproic acid's composition by mass is: C 62.04%, H 10.41%, O 27.55% If a 10.00 g sample of caproic acid is dissolved in 1 L of water, 49.34 ml of 1.745 M sodium hydroxide is required to titrate the solution. What is the molecular formula for caprioc acid? You must show all work to receive any credit. Page 1
1. The SO 2 present in air is mainly responsible for the acid rain phenomenon. Its concentration can be determined by titrating against a standard permanganate solution as follows: 5SO 2 + 2MnO 4 - + 2H 2 O 5SO 4 2- + 2Mn 2+ + 4H + Calculate the number of grams of SO 2 in a sample of air if 7.37 ml of 0.00800 M KMnO 4 solution are required for the titration. A) 9.43 10 3 g B) 5.89 10 5 g C) 7.37 10 3 g D) 2.24 10 4 g 2. A pressure that will support a column of Hg to a height of 256 mm would support a column of water to what height? The density of mercury is 13.6 g/cm 3 ; the density of water is 1.00 g/cm 3. A) 348 cm B) 1.00 10 2 ft C) 18.8 mm D) 33.8 ft E) 76.0 cm 3. Why do astronauts have to wear protective suits when they are on the surface of the moon? A) The atmospheric pressure on the moon is too high, it would crush them. B) The atmospheric pressure on the moon is too low, their cells would all rupture and release gasses, killing them. C) The temperatures are too cold, or too hot, to sustain life for long; and there is no oxygen to breathe. D) both b and c 4. Calculate the volume in ml of a 1.420 M NaOH solution required to titrate 25.00 ml of a 4.500 M H 2 SO 4 solution. A) 56.25 ml B) 158.5 ml C) 112.5 ml D) 225.0 ml Page 2
5. A sample of gas has a volume of 47.0 L at 70.8 C. The gas is heated to 83.8 C at constant pressure. What is the final volume of this gas? A) 48.8 L B) 45.3 L C) 55.6 L D) 2.21e 2 L E) 2.52e 2 L 6. A sample of air occupies 3.8 L when the pressure is 1.2 atm. What pressure is required in order to compress it to 0.075 L? (The temperature is kept constant.) A) 42 atm B) 0.24 atm C) 24 atm D) 61 atm 7. A sample of gas occupies 1.00e3 ml at 25 C and 680 mmhg. What volume will it occupy at the same temperature and 810 mmhg? A) 5.5e8 ml B) 1.2e3 ml C) 5.5e2 ml D) 8.4e2 ml E) 1.2e 3 ml 8. A 50.0 ml sample of 0.436 M NH 4 NO 3 is diluted with water to a total volume of 250.0 ml. What is the ammonium nitrate concentration in the resulting solution? A) 21.8 M B) 0.459 M C) 2.18 10 2 M D) 8.72 10 2 M E) 0.109 M 9. The concentration of a hydrogen peroxide solution can be conveniently determined by titration against a standardized potassium permanganate solution in an acidic medium according to the following equation: 2MnO 4 + 5H 2 O 2 + 6H + 5O 2 + 2Mn 2+ + 8H 2 O If 36.44 ml of a 0.01652 M KMnO 4 solution are required to completely oxidize 25.00 ml of a H 2 O 2 solution, calculate the molarity of the H 2 O 2 solution. A) 1.518 10 3 M B) 6.023 10 4 M C) 0.06020 M D) 0.02012 M Page 3
10. A 0.9182 g sample of CaBr 2 is dissolved in enough water to give 500. ml of solution. What is the calcium ion concentration in this solution? A) 9.19 10 3 M B) 2.30 10 3 M C) 2.72 10 3 M D) 4.59 10 3 M E) 1.25 10 3 M 11. Which of the following is a correct half-reaction for the reaction: 2Sr + O 2 2SrO A) Sr Sr + + e B) Sr + 2e Sr 2 C) Sr Sr 2+ + 2e D) Sr + e Sr 12. Calcium oxalate (CaC 2 O 4 ) is insoluble in water. For this reason it can be used to determine the amount of Ca 2+ ions in fluids such as blood. The calcium oxalate isolated from blood is dissolved in acid and titrated against a standardized KMnO 4 solution by the equation 2MnO 4 + 16H + + 5C 2 O 4 2-2Mn 2+ + 10CO 2 + 8H 2 O. In one test it is found that the calcium oxalate isolated from a 10.0-mL sample of blood requires 24.2 ml of 9.56 10 4 M KMnO 4 for titration. Calculate the number of milligrams of calcium per milliliter of blood. A) 0.231 mg/ml B) 0.542 mg/ml C) 2.96 mg/ml D) 2.31 mg/ml 13. How many moles of MgCl 2 are present in 60.0 ml of 0.100 M MgCl 2 solution? A) 60.0 moles B) 0.572 moles C) 6.00 10 3 moles D) 6.00 moles 14. Oxygen (O 2 ) and carbon dioxide (CO 2 ) are colorless and odorless gases. What chemical test would allow you to distinguish between these two gases? A) Attempt to dissolve each gas in water; oxygen will dissolve, while carbon dioxide will not B) Attempt a combustion reaction, which will work in an atmosphere of oxygen, but not carbon dioxide C) Place gold in the presence of each; gold will oxidize in the presence of oxygen, but not carbon dioxide Page 4
15. A 3.664-g sample of a monoprotic acid was dissolved in water. It took 20.27 ml of a 0.1578 M NaOH solution to neutralize the acid. Calculate the molar mass of the acid. A) 1145 g/mol B) 3198 g/mol C) 578.2 g/mol D) 2121 g/mol 16. When excess AgNO 3 is added to 50.0 ml of a solution of MgCl 2, an AgCl precipitate forms immediately. The precipitate is then filtered from the solution, dried, and weighed. If the recovered AgCl is found to have a mass of 0.1183 g, what was the concentration of magnesium ions in the original MgCl 2 solution? A) 0.300 M B) 8.25 10 3 M C) 1.65 10 2 M D) 2.06 10 5 M E) 4.13 10 3 M 17. Iodate ion, IO 3 -, oxidizes SO 3 2- in acidic solution. The half-reaction for the oxidation is SO 3 2 + H 2 O SO 4 2 + 2H + + 2e A 100.0-mL sample of solution containing 1.390 g of KIO 3 reacts with 32.5 ml of 0.500 M Na 2 SO 3. What is the final oxidation state of the iodine after the reaction has occurred? A) +7 B) +1 C) 0 D) 1 18. What volume of a 0.500 M HCl solution is needed to completely neutralize 10.0 ml of a 0.200 M Ba(OH) 2 solution? A) 10.0 ml B) 0.200 ml C) 2.00 ml D) 8.00 ml Page 5
19. A sample of a gas occupies 1.40 10 3 ml at 25ºC and 760 mmhg. What volume will it occupy at the same temperature and 380 mmhg? A) 2,800 ml B) 2,100 ml C) 1,400 ml D) 1,050 ml E) 700 ml 20. A sample of nitrogen gas has a volume of 32.4 L at 20ºC. The gas is heated to 220ºC at constant pressure. What is the final volume of nitrogen? A) 2.94 L B) 19.3 L C) 31.4 L D) 54.5 L E) 356 L Page 6
Answer Key Word problem: Calculate the molecular mass of caproic acid: 1.745 mol NaOH 1L NaOH 1 mol caproic 49.34 ml NaOH 0.08609 mol caproic 1L NaOH 1000 ml 1 mol NaOH Since the sample of caproic acid is 10.00 g: molecular mass = grams 10.00g mol 0.08609mol 116.16 g/mol If mw = 116.16 and the compound is 62.04% carbon, each molecule must have: 116.16g acid/mol acid?.6204g C/g acid =6 mol C/mol acid 12.01 g C/mol C and: 116.16 g acid/mol acid 0.1041g H/g acid 12 mol H/mol acid 1.008 g H/mol H and: 116.16 g acid/mol acid 0.2755 g O/g acid 2 mol O/mol acid 16.00 g O/mol O and the molecular formula is C H O 1. A 2. A 3. D 4. B 5. A 6. D 7. D 8. D 9. C 10. A 11. C 12. A 13. C 14. B 15. A 16. B 17. C 18. D 19. A 20. D 6 12 2 Page 7