1. Which of the following is NOT a valid definition of an acid?(10 points) (A) A
ID: 993000 • Letter: 1
Question
1. Which of the following is NOT a valid definition of an acid?(10 points)
(A) An electron pair acceptor
(B) A substance that lowers the pOH of a solution
(C) A proton donor
(D) A substance that produces H+ in aqueous solution
2. If the Ka of sulfurous acid is 1.54 x 10-2, what is the Kb of its conjugate base? (10 points)
(A) 1.54 x 10-12
(B) 6.49 x 10-13
(C) 1.30 x 10-12
(D) 6.17 x 10-10
3. What is the Ka of a 0.320 M solution of nitrous acid? Nitrous acid has a pKa of 3.34. (15 points)
(A) 0.320
(B) 2.29 x 10-4
(C) 4.57 x 10-4
(D) 4.57 x 10-6
4. Which of the following is true? (15 points)
(A) pH + pK a = 14
(B) pKb + pOH = 14
(C) pH + pOH = Kw
(D) pKa + pKb = pKw
5. During a titration the following data were collected. A 20.0 mL portion of solution of an unknown acid HX was titrated with 2.0 M KOH. It required 60.0 mL of the base to neutralize the sample. What is the molarity of the acid HX? (15 points)
A) 6.0 M
B) 0.67 M
C) 3.0 M
D) 0.12 M
6. An acid-base titration curve plots(15 points)
A) the pH of a solution against the total volume of an added acid
B) the pH of a solution against the volume of an added acid or base
C) the pH of a solution over time
D) the pH of a solution containing buffers
Explanation / Answer
1) Answer is A. Acid is not an electron pair acceptor, it is donor.
2) For a conjugate acid-base pair, Ka × Kb = Kw where Kw is 1x10-14
Then Kb = Kw/Ka = 1x10-14 / 1.54 x 10-2 = 6.49 x 10-13
3) pKa = -log Ka
3.34 = -log Ka, then Ka = antilog(-3.34)= 4.57x 10-4
4) answer is D. pKa+pKb = pKw
5) No. of moles of KOH required to neutralise the acid = 2 M/1000mL * 60 mL = 0 .12 mols
So 20 mL of acid contains 0.12 mols of acid. Then molarity of the acid = 0.12 mols / 20 mL * 1000 mL = 6M
6) answer is B
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