1aa3-2006-fe-posted

1aa3-2006-fe-posted - Name: _ Student number: _ Page 1 of...

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Name: ____________________ Student number: ______________ Page 1 of 27 Here are questions from the 2006 final exam for Chem 1aa3. Some questions which were not relevant have been removed. ©McMaster University Chemistry Department, 2006 continued on next page
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Name: ____________________ Student number: ______________ Page 2 of 27 Questions 1 through 30 are worth two (2) marks each. 1. Use the data below to calculate the equilibrium constant, K C , for the following reaction: CH 3 COOH(aq) + NO 2 (aq) CH 3 COO (aq) + HNO 2 (aq) K C = ? Data: K a (CH 3 COOH) = 1.8 × 10 –5 K b (NO 2 ) = 2.2 × 10 –11 (A) 2.5 × 10 15 (B) 8.2 × 10 5 (C) 4.0 × 10 –2 (D) 1.2 × 10 –6 (E) 8.2 × 10 –9 2. How many grams of NaCN would you need to dissolve in enough water to make exactly 250. mL of solution with a pH of 10.00? (K b CN = 2.0 × 10 –5 ). (A) 5.00 × 10 –6 g (B) 2.45 × 10 –5 g (C) 1.50 × 10 –4 g (D) 3.90 × 10 –3 g (E) 7.35 × 10 –3 g ©McMaster University Chemistry Department, 2006 continued on next page
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Name: ____________________ Student number: ______________ Page 3 of 27 3. The K a of methanoic acid (HCOOH) is 1.7 × 10 –4 at 25 ° C. Choose the statements that are TRUE regarding this acid. (i) The acid will become stronger at 40 ° C. (ii) A 0.10 M solution of methanoic acid will have a higher percent ionization than a 0.75 M solution. (iii) A 0.75 M solution of methanoic acid will contain a lower concentration of H 3 O + (aq) than a 0.10 M solution. (iv) Its conjugate base, HCOO , is a stronger base than the ethanoate ion (K b of ethanoate ion = 5.6 × 10 –10 ). (A) i, ii (B) i, iii (C) i, iv (D) ii, iii (E) iii, iv 4. Novocaine, which is used by dentists as a ‘local’ anaesthetic, is a weak base. What is the ratio of the concentration of Novocaine to that of its conjugate acid in a patient’s blood plasma (pH = 7.40)? (K b Novocaine = 8.91 × 10 –6 ) (A) 4.47 × 10 –3 (B) 0.0282 (C) 1.86 (D) 35.5 (E) 224 ©McMaster University Chemistry Department, 2006 continued on next page
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Name: ____________________ Student number: ______________ Page 4 of 27 5. Choose, where possible, the stronger Lewis acid from each pair: Fe 2+ , Fe 3+ and BF 3 , BCl 3 The stronger Lewis acids are: (A) Fe 2+ , BF 3 (B) Fe 3+ , BF 3 (C) Fe 2+ , BCl 3 (D) Fe 3+ , BCl 3 (E) Each pair of acids is equally strong. 6. Chlorophenol blue is an acid-base indicator with a pK a of 5.6. The acidic form is yellow and the basic form is red. A few drops of this indicator are added to the titration of caffeine (pK b = 3.4) with HCl. Find the TRUE statement(s) about this titration experiment. (i) The chlorophenol blue indicator is an appropriate choice for locating the equivalence point of this titration. (ii)
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1aa3-2006-fe-posted - Name: _ Student number: _ Page 1 of...

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