Practice Final Exam CH 201

Transcription

1 Practice Final Exam CH 201 Name: (please print) Student I D : Instructions - Read Carefully 1. Please show your work, and put your final answers in the spaces provided. 2. Point values for each question are given in parentheses at the beginning of each question pka s HCN : 9.40 HClO : 7.46 HBrO : 8.70 NH 4 1+ : 9.25 HNO 3 : -1.4 HNO 2 : 3.40 H 2 S : 7.00 HS 1- : H 2 C 2 O 4 : 1.23 HC 2 O 4 1- : 4.19 HCl : -6.1 HN 3 : 4.72 HClO 4 : << 0 H 3 BO 3 : 9.27 H 3 C 2 O 2 H: 4.7 1A 8A 1 H A 3A 4A 5A 6A 7A Li Be B C N O F Na K Rb Cs Fr (223) 12 Mg B 4B 5B 6B 7B 8B 1B 2B 20 Ca Sr Ba Ra Sc Y La Ac Ti Zr Hf Rf (261) 23 V Nb Ta Db (262) 24 Cr Mo W Sg (263) 25 Mn Tc (98) 75 Re Bh (264) 26 Fe Ru Os Hs (265) 27 Co Rh Ir Mt (268) 28 Ni Pd Pt Ds (269) 29 Cu Ag Au Rg (272) 30 Zn Cd Hg Al Ga In Tl Si Ge Sn Pb P As Sb Bi S Se Te Po (209) 17 Cl Br I At (210) 2 He Ne Ar Kr Xe Rn (222) Signature: Pledge: I have neither given nor received help during this exam. Name (print): 1

2 Please solve all problems 1. A. Calculate E o for the cell Given 2 CCCC + 3 SSSS 4+ 3 SSSS CCCC 3+ SSSS ee SSSS 2+ EE 0 = 0.15 VV CCCC ee CCCC EE 0 = 0.74 VV B. Calculate G o for the reaction as well. oo EE cccccccc =. GG oo =. 2. At 25 o C calculate the voltage of the cell Ag(s) Ag + (aq, 0.1M) Cu 2+ oo (aq,0.01 M) Cu if EE cccccccc = V, and given AAAA + + ee AAAA EE 0 = VV CCCC ee CCCC EE 0 = VV VV =. 2

3 3. Balance the equation CCCCOO 3 + NNOO 2 CCCC + NNOO 3 Balanced equation. 4. A. How much heat is required to boil 1 liter of water starting from room temperature of 25 o C? The specific heat of water is 4.18 J/g- o C. q =. B. If the water is heated on a propane stove, then the heat is transferred from the combustion of propane. How many liters of propane are required if the propane is delivered in a pressurized tank with a pressure of 10 atm, assuming that you may treat it as an ideal gas at 298 K. The combustion of propane is given below. CC 3 HH OO 2 3 CCOO HH 2 OO cccccccc HH oo = 2220 kkkk/mmmmmm NOTE: Do not worry about the sign of the heat. Obviously, the heat output from the propane must balance the heat input to the water. Volume =. 3

4 5. Given the following thermochemical equation, calculate the heat involved in decomposing 12.5 g of water to the elements. 2H 2 (g) + O 2 (g) 2H 2 O (l) H = kj \ q =. 6. Will CaSO 4 precipitate if 50 ml of M CaCl 2 is added to 50 ml of M Na 2 SO 4? (K sp for CaSO 4 = 2.4 x 10-5 ) Answer =. 4

5 7. Given the thermochemical equation 2NO(g) + O 2 (g) 2NO 2 (g) H = kj, calculate H for the following reaction: NO 2 (g) NO(g) + 1/2 O 2 (g) H =. 8. A 15.0-g block of aluminum at an initial temperature of 27.5 C absorbs kj of heat. What is the final temperature of the block? (The specific heat of Al is J g -1 C -1.) T =. 5

6 9. Use the following thermochemical equations C 2 H 2 (g) + 5/2 O 2 (g) 2CO 2 (g) + H 2 O(g) H = kj C 2 H 6 (g) + 7/2 O 2 (g) 2CO 2 (g) + 3H 2 O(g) H = kj H 2 (g) + 1/2 O 2 (g) H 2 O(g) H = -286 kj to calculate H for the following reaction: C 2 H 2 (g) + 2H 2 (g) C 2 H 6 (g) H =. 10. A volume of 50.0 ml of M HBr at C is added to 50.0 ml of NaOH, also at C. The final temperature is C. Calculate the enthalpy change, H, in kj for the following reaction: HBr(aq) + NaOH(aq) --> NaBr(aq) + H 2 O (l) The heat capacity of the system is J/ C. C =. 6

7 11. The molar solubility of PbCl 2 in 0.10 M NaCl is 1.7 x 10-3 moles in a liter (that is 1.7 x 10-3 moles of PbCl 2 will dissolve in 1 liter of the solution). What is the K sp of PbCl 2? Solution: K sp =. 12. A. Determine the equilibrium constant for the reaction, HHHH + CCCC 1 HHHHHH + FF 1 B. Calculate G o. K =. G o =. 7

8 13. Acid rain is caused by industrial emissions of SO 3, which combine with water to form H 2 SO 4. If the SO 3 pressure is 6 x 10-7 atm and the equilibrium constant for hydration, SSOO 3 (gg) SSOO 3 (aaaa) Is KK = [SSOO 3] PP SSSS3 = 5 MM/aaaaaa NOTE: We write the equilibrium constant this way with units, but we know that these are relative to the standard state of 1 atm of pressure and 1 molar of solution. K actually has no units, but the concentration [SSOO 3 ] is in units of molarity and PP SSSS3 is in units of atm. Assume that the equilibrium lies far to the right so all of the dissolved SO 3 forms H 2 SO 4. SSOO 3 (aaaa) + HH 2 OO HH 2 SSOO 4 (aaaa) ph =. 14. Acetic acid buffers are used to buffer ph values less than 7. A. What is the optimum buffer ph for acetic acid? B. What is the range of the acetic acid buffer system (i.e. what are the limits in terms of low and high ph)? C. Starting with a total of 0.1 M acetic acid, determine the concentration of [acetate] at three ph values, the low end, optimum and high end of the buffer region. A. Optimum ph =. B. Low and high ph =. C. Acetate concentration (M) under three ph conditions Low Optimum High 8

9 15. Determine the ph when 60 ml of a 0.1 M solution of NaCN is mixed with 10 ml of a solution of 0.4 M NaOH. The pk a of HCN is 9.4. ph = grams of an unknown solute were dissolved in 40.0 g of tetrahydrofuran (C 4 H 8 O). The boiling point of the solution was measured to be 67.0 o C. What is the molar mass of the unknown? The physical data are given below. Boiling point T vap = 66 o C Enthalpy of vaporization vap H o = 32 kj/mol. K b = K/molal MM ssssssssssss =. 17. An non-ionic solution of has a rise in height of 0.1 cm in the molar mass osmometer. A. Calculate the concentration of the solute. Concentration =. 9

10 B. The technician dissolved 5 mg./ml to obtain this result. What is the molar mass of the ionic solute. MM mm =. 18. A solution is prepared by dissolving 40.5 g of LiF in 225 g of water. If the vapor pressure of pure water is 21.8 torr at this temperature, what is the vapor pressure of the solution? vapor pressure = 10

11 19. Determine the entropy and average energy of each of the systems shown in the figure below. Give the energy in the units of the systems. We can just call them energy units. The entropy can be calculated using SS = kk BB llllll S for system A =. S for system B =. E for system A =. E for system B =. 20. Consider the following reaction: 2 HBr(g) + Cl 2 (g) 2 HCl(g) + Br 2 (g) At the reaction temperature of 320 K, K = 250. During the reaction, the reaction mixture was sampled and the following pressures were found: P(HBr) = 0.15 atm P(Cl 2 ) = atm P(HCl) = 0.48 atm P(Br 2 ) = 1.00 atm a) What is the value of Q? Q= 11

12 b) What is the value of G at the reaction temperature? GG = kj 21. Use the following data in the table to find the rate law for the reaction, dd[aa] dddd Time (sec) [A](M) ln([a]) 1/[A] = kk[aa]nn n =. 22. For the reaction of propene with benzene to make cumene, the rate constant is observed to increase from k = 10-4 M -1 s -1 to k = 3 x 10-4 M -1 s -1 at 25 o C and 45 o C, respectively. Determine the Arrhenius parameters A and E a for this process. EE aa =. A =. 12

13 23. The first-order decomposition of a colored chemical species, X, into colorless products is monitered with a spectrophotometer by measuring changes in absorbance over time. Species X has a molar absorptivity constant of 5 x 10 3 M -1 cm 1 and the pathlength of the cuvette containing the reaction mixture has a path length of 1.00 cm. The data from the experiment are given in the table below. [X](µM) Absorbance Time (min)? ? A.Calculate the initial concentration of the unknown species. concentration =. B. Calculate the rate constant for the first order reaction using the values given for concentration and time. Include units with your answers. k =. C. Calculate the number of minutes it takes for the absorbance to drop from to D. Calculate the half-life of the reaction. Include units with your answer. t =, ττ 1/2 =. 13