CHEN 1211 Midterm: chen1211_u_2

The following questions involve a hypothetical weak acid (HB). a. Given the equation below for the dissociation of this acid in water, Identify the Bronsted acids and bases in the reaction. HB(aq) + H_2O(l) rightarrow H_3O^+(aq) + B^+(aq) b Determine the K_a and % dissociation of this acid if a 0.50M solution has a pH of 2.75. c. If 50.0ml of a 0.20M weak acid is titrated with 0.10M NaOH, what is the pH after 40.0ml of the base is added? d. What is the pH of the solution at the equivalence point of the titration described in C above? e. Use Le Chatelier's principle to explain how the addition of the OH^- ions first creates a buffer solution and then a solution of weak base at the equivalence point. f Sketch the titration curve for this titration. Label the axis, the 1/2 way point and the equivalence point.

A buffer contains 050 mol NH^+_4 and 0.50 mol NH_3 diluted with water to 1.0 L. How many moles of NaOH are required to increase the pH of the buffer to 10.00^+ (pk_a of NH^+_4 = 9.25) a. 0.035 mol b. 0.15 mol c. 0.35 mol d. 0.41 mol e. 2.8 mol Which of the following conditions metal the equivalence point of the titration of a monophonic weak base with a strong acid? 1. The moles of acid added from the buret equals the initial moles of weak base. The volume of acid added from the buffer must equal the volume of base titrated. 3 The pH of the solution is less than 7.00 a. 1 only b 2 only c. 3 only d. 1 and 3 e. 2 AND 3 A volume of 25.0 ml of 0.100M CaH_3CO0_2H(aq) is titrated with 0.1000 M NaOH(aq). What is the pH after the additions of 12.5 mL of NaOH? (K_a of benzoic acid = 63 times 10^-5) a. 2.00 b. 4.20 c. 5.40 d. 7.00 e. 8.60