Sample Midterm 2 Solutions

Sample Midterm 2 Solutions - 1 Chemistry 102 Sample Midterm...

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1 Chemistry 102 Sample Midterm #2 Solutions Section E2, Brown 1. (8 marks) (a) (3 marks) Determine if the following substances yield acidic, basic or neutral aqueous solutions: ANSWER: Lithium hypochlorite: Li + conjugate to strong base, OCl - conjugate base to weak acid 1/2 therefore basic 1/2 NH 4 F : K a (NH 4 ) = K w /K b = 5.6x10 -10 ; K b (F - ) = K w /K a = 1.5 x 10 -11 1/2 acidic 1/2 [CH 3 NH 3 ]CN : K a (CH 3 NH 3 ) = K w /K b = 2.4x10 -11 ; K b (CN - ) = K w /K a = 1.6 x 10 -5 1/2 basic 1/2 (b) (2 marks) Write the dominant acid/base equilibrium reaction for each of the following solutions: ANSWER: A solution was produced from adding NaClO 2 (s) to water: ClO 2 - (aq) + H 2 O (l) ! HClO 2 (aq)+ OH - (aq) 1 A 1.0 M solution of HCN (aq) is treated with an equal volume of 1.0 M NaOH (aq): CN - (aq) + H 2 O (l) ! HCN (aq)+ OH - (aq) 1 (c) ( 3 marks) Using the information for these reactions at 500 o C: 1) 2 NO 2 (g) ! 2 NO (g) + O 2 (g) K = 1.95 " 10 -5 2) 2 N 2 O (g) ! 2 NO (g) + N 2 (g) K = 192.35 3) 2 NO 2 (g) ! N 2 O 4 (g) K = 4 determine the equilibrium constant for this reaction also at 500 o C: 4) 2 N 2 O (g) + O 2 (g) ! 2 NO 2 (g) + N 2 (g) ANSWER: Reaction (4) = reaction (2) - reaction (1) 1 K 4 = K 2 /K 1 = 9.8 " 10 6 2
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2 2. (9 marks) At 373 K, a reaction for the production of chlorine gas is: 4 HCl (g) + O 2 (g) ! 2 H 2 O (g) + 2 Cl 2 (g) K = 1.96 " 10 9 Determine the equilibrium partial pressure of all gases at 373 K, from the initial conditions of: P HCl = 0.5 atm P O2 = 0.1 atm P H2O = 0.1 atm P Cl2 = 0.2 atm ANSWER: (OPTION 1)
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Sample Midterm 2 Solutions - 1 Chemistry 102 Sample Midterm...

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