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Practice Quiz 2A ANSWER KEY 2009

# Practice Quiz 2A ANSWER KEY 2009 - CHM 2046 Answer Key Quiz...

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CHM 2046 Answer Key - Quiz 2A Spring, 2006 Answer all questions. Be careful to give your final answer to the correct significant figures. 1. a) (3 points) The acetate ion (CH 3 COO - ) is a weak base. Write down the base-ionization equation for CH 3 COO - in water. CH 3 COO - (aq) + H 2 O (l) CH 3 COOH (aq) + OH - (aq) b) (2 points) Complete the expression for the base-ionization constant (K b ) for CH 3 COO - . K b = ] COO [CH ] COOH][OH [CH - 3 - 3 c) (5 points) Calculate the pH of a 0.40 M solution of CH 3 COO - (K a for CH 3 COOH = 1.8 x 10 -5 ). CH 3 COO - (aq) + H 2 O (l) CH 3 COOH (aq) + OH - (aq) I 0.40 - 0 0 C -x +x +x E (0.40-x) - x x K b for CH 3 COO - =K w /K a (CH 3 COOH)=(1.0 x 10 -14 )(1.8 x 10 -5 ) = 5.6 x 10 -10 K b = x 2 /(0.40-x) x 2 /0.40 x = [OH - ] = 1.50 x 10 -5 pOH = 4.82 pH = 9.18 2. a) (3 points) Calculate the pH when 100 mL of 0.100 M Ca(OH) 2 solution is added to 50 mL of 0.400 M HCl solution. Ca(OH) 2 (s) + H 2 O (l) Ca 2+ (aq) + 2 OH - (aq) HCl (g) + H 2 O (l) H 3 O + (aq) + Cl - (aq) n(OH - ) = MV = (2)(0.100 M)(100 x 10 -3 L) = 0.200 moles n(H 3 O + ) = MV = (0.400 M)(50 x 10 -3 L) = 0.20 moles OH - and H 3 O + neutralize exactly pH = 7.00 b) (2 points)

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