CHM 101 Fall 2022 Exam 2 Version 4 Answers

CHM 101-Fall 2022-Exam 2-Version 4 Key 1. Calculate the molar mass, MM, (or molecular weight) of Fe3(PO4)2. A. B. C. D. E. 237.6 g/mol 262.5 g/mol 525.1 g/mol 357.5 g/mol 245.8 g/mol 2. Calculate the number of moles of aluminum chloride, AlCl 3 (MM = 133.3 g/mol), in a 50.0-gram sample. A. B. C. D. E. 0.666 mol 0.123 mol 0.375 mol 0.801 mol 6.66 × 103 mol 3. If 1.10 × 1024 molecules of a substance have a mass of 440.0 g, what is the molar mass of this substance? A. B. C. D. E. 4.00 × 10–22 g/mol 4.15 × 10–3 g/mol 72.3 g/mol 145 g/mol 241 g/mol 4. How many fluoride, F–, ions are present in 1.20 mol of BaF2 dissolved in a 600.0-mL solution? A. B. C. D. E. 1.99 × 10–24 F– ions 7.23 × 1023 F– ions 2.40 F– ions 1.45 × 1024 F– ions 42.5 F– ions 5. Which of the following elements contains the most atoms in a 100.0-gram sample of the element? A. Boron B. Nitrogen C. Gold D. Argon E. Phosphorus 6. Barium sulfate, BaSO4, is a compound used to assist in diagnosing medical problems through x-ray analysis and is 58.8% barium. What mass of barium is present in a 620-mg tablet of barium sulfate? A. B. C. D. E. 11 mg 365 mg 83 mg 230 mg 1.1 × 103 mg 7. A 5.05-gram sample of a silicon compound contains 2.36 g of Si. The other element in the compound is oxygen. What are the percentages of silicon and oxygen in this compound, respectively? A. B. C. D. E. 70.1% Si and 29.9% O 46.7% Si and 53.3% O 53.3% Si and 46.7% O 63.7% Si and 36.3% O 29.9% Si and 70.1% O -1- CHM 101-Fall 2022-Exam 2-Version 4 Key 8. A compound with the empirical formula CH2O has a molar mass of approximately 90.08 g/mol. What is its molecular formula? A. B. C. D. E. C4H8O4 CH2O C3H6O3 C5H10O5 C6H12O6 9. Calculate the molarity of a solution consisting of 15.0 g of NaCl (MM = 58.5 g/mol) in 2.00 L of solution. A. B. C. D. E. 0.668 M 0.128 M 0.938 M 1.26 M 7.5 M 10. If 50.0 mL of a 0.235 M NaCl solution is diluted to 200.0 mL, what is its new concentration? A. B. C. D. E. 0.0588 M 0.0118 M 0.0426 M 1.18 M 58.5 M 11. The combustion of pentene (C5H10) proceeds according to the following unbalanced equation: __C5H10(g) + __O2(g) → __CO2(g) + __H2O(g) When this equation is balanced properly, what is the coefficient for O2? A. 5 B. 10 C. 15 D. 32 E. 42 Questions 12-15 are related by the solubility rules. 12. Write a balanced equation for the dissolving of magnesium nitrate, a soluble ionic compound, in water. A. B. C. D. E. Mg(NO3)2(s) → Mg2+(aq) + 2 NO3–(aq) Mg(NO3)2(s) → Mg(s) + 2 NO3(aq) Mg(NO3)2(s) → Mg+(aq) + (NO3–)2(aq) Mg(NO3)2(s) → Mg(s) + N2(g) + 3 O2(g) Mg(NO3)2(s) → Mg(aq) + (NO3)2(aq) 13. Which of the following is most likely to be insoluble when mixed with water? A. B. C. D. E. PbSO4 Li2CO3 KOH Ba(NO3)2 NH4NO3 14. When aqueous solutions of K2CO3 and CaCl2 are mixed, what is the correct formula for the precipitate? A. ClCO3(s) B. KCl(s) C. K2Ca(s) -2- D. K2Cl2(s) E. CaCO3(s) CHM 101-Fall 2022-Exam 2-Version 4 Key 15. When Ca(NO3)2(aq) and K2SO4(aq) are mixed, a double-displacement (exchange) reaction occurs in which a solid precipitate forms. What is the net ionic equation for this reaction? A. B. C. D. E. Ca(aq) + SO4(aq) → CaSO4(g) NO3−(aq) + K+(aq) → KNO3(s) Ca(aq) + S(aq) + 2 O2(aq) → CaSO4(s) Ca2+(aq) + SO42−(aq) → CaSO4(s) (NO3)2(aq) + K2(aq) → K2(NO3)2(s) Questions 16-20 are concerned with reactions other than double-displacement (exchange) reactions. 16. The image below depicts a reaction involving sodium and chlorine. How should this reaction be classified and what is the product of this reaction? A. B. C. D. E. Decomposition; Cl2(s) Composition; NaCl(g) Displacement; NaCl(s) Composition; NaCl(s) Decomposition; Na(s) 17. Platinum(IV) chloride decomposes to its elements upon heating. Which equation best represents this reaction? A. B. C. D. E. PtCl(s) → Pt(s) + Cl(g) PtCl4(s) → Pt(s) + Cl4(g) PtCl4(s) → Pt(s) + 4 Cl(g) PtCl4(s) → Pt(s) + 2 Cl2(g) 2 Pt4Cl(s) → 8 Pt(s) + Cl2(g) 18. Lithium chloride can be synthesized by a reaction between lithium metal and chlorine gas. Which equation best represents this reaction? A. B. C. D. E. 2 Li(s) + Cl2(g) → 2 LiCl(s) 4 Li(s) + 3 Cl2(g) → 2 Li2Cl3(s) 2 Li(s) + 3 Cl2(g) → 2 LiCl3(s) Li(s) + Cl(g) → LiCl(s) Li(s) + Cl2(g) → LiCl2(s) 19. Given that: 2 Na(s) + Cl2(g) → 2 NaCl(s) Which of the following is not conserved in this balanced equation that synthesizes NaCl from the elements? A. B. C. D. E. Total mass of all substances Total moles of sodium atoms Total moles of chlorine atoms Total moles of all atoms Total moles of all molecules -3- CHM 101-Fall 2022-Exam 2-Version 4 Key 20. Which of the following metals will react with aqueous zinc nitrate in a single-displacement reaction to produce zinc metal? Hint: Consult the activity series. A. B. C. D. E. Tin Aluminum Cadmium Silver Cobalt 21. Which of the following elements is known to exist naturally as diatomic molecules? A. B. C. D. E. Chromium Bromine Gallium Helium Magnesium 22. How much heat energy would be needed to raise the temperature of a 22.3-g sample of aluminum from 22.5°C to 55.0°C? (Caluminum = 0.895 J/g-ºC) A. B. C. D. E. 20.0 J 449 J 649 J 725 J 1.10 × 102 J 23. Given that: 4 PH3(g) + 8 O2(g) → P4O10(s) + 6 H2O(g) If 9.2 mol of PH3 react with excess oxygen, how many moles of P4O10 should form? A. B. C. D. E. 4.0 mol 2.3 mol 9.2 mol 6.0 mol 3.7 mol 24. Given that: 4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(g) If 82.0 g of NH3 react with sufficient oxygen, how many grams of NO should form? A. B. C. D. E. 46.5 g 11.6 g 186 g 145 g 580 g 25. Given that: 2 Fe(s) + 3 Cl2(g) → 2 FeCl3(s) If 35.0 g of each of iron and chlorine are combined, how much FeCl 3 (MM = 162.2 g/mol) should form? Hint: Determine the limiting reactant. A. B. C. D. E. 68.0 g 80.0 g 155 g 102 g 53.3 g -4-