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Exam_2_Fall_2009_Key - MONTGOMERY COLLEGE Chem 101(Bontems...

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Unformatted text preview: MONTGOMERY COLLEGE Chem 101 (Bontems, Fall, 2009 MWF) Exam #2 Name: ____Key__________________________ Multiple Choice – In the blank, write the letter of the best answer. (3 pts. ea.) 1. C_______ Which of the following is correct? a. n is indirectly proportional to V c. P is directly proportional to T b. P is directly proportional to V d. none of these 2. B_______ The pressure of 3 L of gas in a flexible container is tripled then its Kelvin temperature is doubled. The volume is now _________. a. 1 L c. 3 L b. 2 L d. 18 L e. none of these 3. B_______ The following reaction is done at constant T and P: CH4(g) + H2O(g) CO(g) + 3H2(g) . What happens to the volume as the reaction proceeds? 2 mole 4 mol a. It remains the same because the reaction is at constant T and P. b. The volume doubles. c. The volume halves. d. None of these. 4. A_______The density of xenon gas at STP is 131 g/mol x (1mol/22.4L) = 5.86 g/L a. 5.86 g/L c. 22.4 g/L b. 0.171 g/L d. none of these 5.C_______How many moles of neon gas are in 3.00 L at STP? 3 L x (1mol/22.4L) = a. 67.2 moles c. 0.134 moles b. 0.179 moles d. not enough information 6. B_______Which gas will sink in air at 25°C and 1 atm? a. HF c. N2 b. SO2 d. none of these e. all of these 7. C_______Which of the following are non‐electrolytes? HCN, K3PO4, C3H8O a. HCN c. C3H8O b. K3PO4 d. more than one of these 8. C Which of the following substances would strongly conduct electricity when dissolved? a. H2SO3 c. HNO3 b. AgCl d. Fe(OH)3 9. C_______ Which of the following would produce five ions per formula unit when dissolved? Na2SO3 AlPO3 Ba3(PO4)2 LiNO3 d. LiNO3 a. Na2SO3 b. AlPO3 e. more than one of these c. Ba3(PO4)2 2 10. C_______ How many moles of nitrate ion are in 2.00 L of 3.00 M Ba(NO3)2? a. 3.00 moles d. 36.0 moles b. 6.00 moles e. none of these c. 12.0 moles 11. D_______ What is the partial pressure of hydrogen in a container that contains 0.25 mol H2 and 0.75 mole O2 and has a total pressure of 4.0 atm? a. 4.0 atm c. 2 atm b. 3.0 atm d. 1 atm e. insufficient information 12. True or False (2 pts each) __T____ HF is a weak acid. __F___ If a solution is diluted, the molarity will increase. __F____ A 2 M solution of HBr contains the same concentration of bromide as a 2 M solution of BaBr2. __T___ The following is an oxidation‐reduction reaction: 2Na + Cl2 2NaCl __F____ The major component of air is oxygen. __F____ NaOH is a weak base. __F____ All soluble compounds are strong electrolytes. ‐1 13. Assign oxidation numbers to each atom of the following: MnO4 F2 (6 pts) Mn __+7____ O __‐2______ F ___0_____ 14. Define each of the following: (3 pts each) Diffusion = migration of a substance from an area of high concentration to an area of low concentration until they are equal. Neutralization reaction is a reaction between and acid and a base to create neutral compounds. 15. List the two conditions which cause real gases to deviate from the ideal gas law. (4 pts) High P and Low T 3 16. A 1.20 g sample of dry ice (CO2) is added to a 755 mL flask containing nitrogen gas at a temperature of 25.0°C and a pressure of 725 mmHg. The dry ice is allowed to sublime (convert from solid to gas) and the mixture is allowed to return to 25.0°C. What is the partial pressure of CO2 and what is the total pressure in the flask? (7 pts) PCO2 =672 mmHg or 0.885 atm Ptot = 1,397 mmHg or 1.84 atm 17. A gas sample is contained in a 39.1 L cylinder at 750 mm Hg and 20.0°C. If the pressure in unchanged, calculate the temperature needed to cause the gas to expand to 50.0L. (6 pts) T2 = 375K 18. What volume of H2 gas (in L) at 748 mmHg and 86°C is needed to synthesize 25.8 g CH3OH? (8 pts) Molar masses: 30.0 1.02 32.0 CO(g) + 2H2(g) CH3OH(g) 48.2 L of H2 gas 4 19. Lead ions can be precipitated from solution with KCl according to the following reaction: Pb 2+ + 2KCl PbCl2(s) Molar masses: 207.2 74.6 278.1 When 28.5 g KCl are added to a solution containing 25.7 g Pb 2+, a PbCl2 precipitate forms. The precipitate is filtered and dried and found to have a mass of 29.4 g. Determine the limiting reactant, theoretical yield of PbCl2 and percent yield for the reaction. (8 pts) From KCl 53.1 g PbCl2 (reject this as too high – put an X through it) From Pb2+ 34.5 g PbCl2 (This lower number is the correct theoretical yield.) Pb2+ is the limiting reagent. % yield = 85.2% 18. Write full balanced equations, full ionic equations and net ionic equations for the following reactions: (8 pts) a. 2HF + Ba(OH)2 → 2H2O + BaF2 Do these as done in lab. Don’t ionize water or HF (weak). b. Pb(NO3)4 + 4LiOH → Pb(OH)4 + 4LiNO3 Do these as done in lab. Ionize all except Pb(OH)4. Bonus: Describe the pickle demonstration and the SF6 demonstration (video) and the scientific principle being demonstrated. ...
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