YORK COLLEGE/CUNY Chemistry 108 Exam 2 | 2022 UPDATE

YORK COLLEGE/CUNY Chemistry 108 Exam 2 Part I: Multiple Choice (60 pts) 1. What is the molecular mass of Br2? A) 79.90 amu B) 79.90 g C) 159.8 amu D) 159.8 g E) 2.65 x 10-22 amu 2. Which one of the following does not represent 1.000 mol of the indicated substance? A) 6.022 × 1023 C atoms B) 26.00 g Fe C) 12.01 g C D) 65.39 g Zn E) 6.022 × 1023 Fe atoms 3. Boron obtained from borax deposits in Death Valley consists of two isotopes. They are boron-10 and boron-11 with atomic masses of 10.013 amu and 11.009 amu, respectively. The atomic mass of boron is 10.81 amu (see periodic table). Which isotope of boron is more abundant, boron-10 or boron-11? A) Cannot be determined from data given B) Neither, their abundances are the same. C) Boron-10 D) Boron-11 4. How many C atoms are in 5.50 g of C? A) 5.01 x 1022 C atoms B) 3.31 x 1024 C atoms C) 6.02 x 1023 C atoms D) 2.76 x 1023 C atoms E) 5.50 x 1023 C atoms Page 2 5. Calculate the average atomic mass of lithium using the following data: Isotope Abundance Mass 6Li 7.5 % 6.0151 amu 7Li 92.5% 7.0160 aum A) 6.51 amu B) 6.02 amu C) 6.94 amu D) 7.02 amu E) 6.50 amu 6. Determine the number of moles of aluminum in 96.7 g of Al. A) 0.279 mol B) 3.58 mol C) 7.43 mol D) 4.21 mol E) 6.02 × 1023 mol 7. Calculate the molar mass of Ba(NO3)2. A) 199.3 g/mol B) 323.3 g/mol C) 247.3 g/mol D) 261.3 g/mol E) 398.6 g/mol 8. What is the mass of 0.0250 mol of P2O5? A) 35.5 g B) 5676 g C) 0.0250 g D) 1.51 × 1022 g E) 3.55 g 9. A compound with an empirical formula of C2H2Br3 has a molar mass of 531.47 g/mol. What is the molecular formula? A) C2H2Br3 B) C4H4Br6 C) CHBr D) C4H4Br3 E) C6H6Br9 Page 3 10. An average atom of uranium (U) is approximately how many times heavier than an atom of potassium? A) 6.1 times B) 4.8 times C) 2.4 times D) 12.5 times E) 7.7 times 11. The empirical formula of a compound of uranium and fluorine that is composed of 67.6% uranium and 32.4% fluorine is A) U2F B) U3F4 C) UF4 D) UF6 E) UF8 12. Chlorine gas reacts with phosphorus to produce phosphorus pentachloride. How many grams of PCl5 are produced from 3.5 g of Cl2 and excess P? 5Cl2(g) + 2P(s)  2PCl5(s) A) 1.4 g B) 4.1 g C) 8.2 g D) 0.020 g E) 730 g 13. Balance the following and list the coefficients in order from left to right. ___ Cr + ___ H2SO4  ___ Cr2(SO4)3 + ___ H2 A) 2, 3, 1, 2 B) 2, 3, 1, 3 C) 1, 3, 1, 3 D) 4, 6, 2, 6 E) 1, 3, 1, 2 14. Which of the following compounds is a strong electrolyte? A) H2O B) N2 C) CH3COOH (acetic acid) D) CH3CH2OH (ethanol) E) KOH Page 4 15. Identify the major ionic species present in an aqueous solution of K2SO4. A) K 2+, S6+, O4 8– B) K 2+, S6+, 4O2– C) 2K+ , S6+, O4 8– D) 2K+ , S6+, 4O2– E) 2K+ , SO4 2– 16. What mass of C12H22O11 (sucrose) is needed to prepare 255 mL of a 0.570 M solution of sucrose in water? A) 49.8 g B) 145 g C) 153 g D) 0.145 g E) 447 g 17. The distinguishing characteristic of all electrolyte solutions is that they A) contain molecules. B) conduct electricity. C) react with other solutions. D) always contain acids. E) conduct heat. 18. Predict the products of the following single replacement reaction. Ni(s) + Cu(NO3)2(aq)  A) No reaction occurs B) NiNO3(aq) + CuNO3(aq) C) NiCu(aq) 2 NO3 - (aq) D) Ni(NO3)2(aq) + Cu(s) E) Ni(NO3)2(aq) + Cu2+(aq) 19. What type of reaction is the following? C2H4(g) + 3 O2(g)  2 CO2(g) + 2 H2O(g) A) Combination reaction B) Acid-base neutralization reaction C) Hydrogen displacement reaction D) Disproportionation reaction E) Combustion reaction Page 5 20. A 50.0 mL sample of 0.436 M NH4NO3 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 Part II: Short Answer (40 pts) 1. (A) Write the balanced molecular equation for the reaction that would occur between CaCl2(aq) and Na2CO3(aq). (B) Write the full ionic and net ionic equations. Finally, (C) Identify the the spectator ions. Be sure to include the correct states in all your equations (15 points). Page 6 2. Nitric oxide (NO) can be prepared by reacting 155 g of ammonia and 356 g of oxygen. 4NH3 + 5O2  4NO + 6H2O A. What is the limiting reagent in this procedure? B. Based on your answer to part A, what mass of NO could theoretically be formed? C. A student who carried out this reaction obtained 232 g of NO. What was the percent yield for this reaction? (20 points) 3. We can theorize that reactions will be 100% efficient based on stoichiometric ratios and the law of conservation of mass. However, chemical reactions do not generally produce 100% yield (theoretical yield). Can you think of a couple things that might happen in the course of a chemical reaction that would lead to lower than 100% yield? (5 pts)