Download Acid Base - Solutions for Homework 6 | CH 302 and more Quizzes Chemistry in PDF only on Docsity!
This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering.
001 10.0 points Which of the following is true in pure water at any temperature?
- pH = 7.0 or greater than 7.
- [H 3 O+][OH−] = 1.0 × 10 −^14
- [H 3 O+] = [OH−] correct
- Kw decreases with increasing tempera- ture.
- pH = 7.
Explanation: Kw is shown to INCREASE with increas- ing temperature. pH = 7 is only true when water is at 24◦C. [H 3 O+][OH−] = Kw, which increases with temperature. At high temperatures pH can be less than
- Thus [H 3 O+] = [OH−] is the only case that is true.
002 10.0 points What is [H 3 O+] when [OH−] = 3. 3 × 10 −^9 M?
- 3 × 10 −^9 M
- 3 × 10 −^5 M
- 0 × 10 −^7 M
- 6 × 10 −^5 M
- 0 × 10 −^6 M correct
Explanation: [OH−] = 3. 3 × 10 −^9 M
Kw = [H 3 O+][OH−] = 1 × 1014
[H 3 O+] =
Kw [OH−]
=
1. 0 × 1014
3. 3 × 10 −^9
= 3. 0 × 10 −^6 M
003 10.0 points What is [OH−] in a 0.0050 M HCl solution?
- 1 .0 M
- 0 × 10 −^3 M
- 0 × 10 −^7 M
- 6 × 10 −^5 M
- 0 × 10 −^12 M correct
Explanation: [OH−] = 0.0050 M Since HCl is a strong acid, it completely dissociates and H+^ is 0.0050 M.
HCl ⇀↽ H+^ + Cl−
Kw = [H+][OH−] = 1 × 10 −^14
[OH−] =
Kw [H+]
=
1 × 10 −^14
= 2 × 10 −^12 M
004 10.0 points What is the conjugate acid of NO− 3?
- HNO 3 correct
- OH−
- NH 3
- NO 2 −
- H+
- NO 32 −
Explanation: Since the question asks for the conjugate acid, we can assume NO− 3 is acting as a base. This means that it is a proton acceptor. To form the conjugate acid, it accepts a H making HNO 3.
005 10.0 points Which is NOT a conjugate acid-base pair?
- H 2 SO 4 : SO^24 − correct
- H 3 SO+ 4 : H 2 SO 4
- H 2 : H−
- HCl : Cl−
- H 2 O : OH−
Explanation: Except for H 2 SO 4 and SO^24 − , the members of all of the pairs differ by one proton.
006 10.0 points The hydronium ion concentration in a solu- tion at pH 10 has what relationship to the hydronium ion concentration in a solution at pH 13?
- 3 times greater than
- 1,000 times greater than correct
- 100 times less than
- 1,000 times less than
Explanation: For pH 10, MH+ = 1 × 10 −^10 For pH 13, MH+^ = 1 × 10 −^13 007 10.0 points Which pH represents a solution with 1000 times higher [OH−] than a solution with pH of 5?
- pH = 4
- pH = 5000
- pH = 2
- pH = 1
- pH = 3
- pH = 8 correct
- pH = 0.
- pH = 7
- pH = 6 Explanation: pH = 5
pOH = 14 − pH = 14 − 5 = 9
[OH−] = 10−pOH^ = 10−^9 M
[OH−]x = 1000 [OH−] = (10^3 )(10−^9 M) = 10−^6 M
pOHx = − log(OHx) = 6
pHx = 14 − pOHx = 14 − 6 = 8
008 10.0 points At 25◦^ C, water solutions which are neutral have a pH of
- infinity.
- about 14.
- about 0.
- about 7. correct Explanation:
009 10.0 points Calculate the resulting pH if 365 mL of 2. M HNO 3 is mixed with 335 mL of 1.10 M Ca(OH) 2 solution.
- 0.350 correct
From the 1:1 mole ratio in the balanced chem- ical reaction we know we would need 0. moles of NaOH to neutralize 0.00905 moles HCl. This is the amount of HCl that must have been in the 181 mL sample. Molarity is moles solute per liter of solution:
? M HCl =
0 .00905 mol NaOH 0 .181 L solution = 0.05 M HCl
012 10.0 points A 0.28 M solution of a weak acid is 3.5% ionized. What is the pH of the solution?
- 2.01 correct
Explanation: M = 0.28 M P = 3.5% 3 .5% of the 0.28 M is ionized (contributes to pH), so
[H+] = (0.28 M) ×
= 0.0098 M
pH = − log[H+] = − log(0.0098) = 2. 00877
013 10.0 points A 0.200 M solution of a weak monoprotic acid HA is found to have a pH of 3.00 at room temperature. What is the ionization constant of this acid?
- 1.0× 10 −^6
- 2.0× 10 −^9
- 2.0× 10 −^5
- 5.0× 10 −^3
- 5.0× 10 −^6 correct
- 1.0× 10 −^3
- 1.8× 10 −^5 Explanation:
014 10.0 points Assume that five weak acids, identified only by numbers (1, 2, 3, 4, and 5), have the following ionization constants.
Ionization Acid Constant Ka value 1 1. 0 × 10 −^3 2 3. 0 × 10 −^5 3 2. 6 × 10 −^7 4 4. 0 × 10 −^9 5 7. 3 × 10 −^11
The anion of which acid is the strongest base?
- 3
- 2
- 4
- 1
- 5 correct Explanation:
015 10.0 points What is the percent ionization for a weak acid HX that is 0.40 M? Ka = 4. 0 × 10 −^7.
- 2.0%
- 0.10% correct
- 0.050%
- 0.00020%
Explanation:
016 10.0 points A 0.00100 M solution of a weak acid HX is 2% ionized. Calculate Ka for the acid.
Correct answer: 4. 08163 × 10 −^7.
Explanation:
017 10.0 points The term “Ka for the ammonium ion” de- scribes the equilibrium constant for which of the following reactions?
- NH+ 4 + H 2 O ⇀↽ NH 3 + H 3 O+^ correct
- NH+ 4 + OH−^ ⇀↽ NH 3 + H 2 O
- NH 4 Cl(solid) + H 2 O ⇀↽ NH+ 4 + Cl−
- NH 3 + H 2 O ⇀↽ NH 4 +^ + OH−
- NH 3 + H 3 O+^ ⇀↽ NH+ 4 + H 2 O
- The term is misleading, because the am- monium ion is not an acid.
Explanation:
018 10.0 points Hydroxylamine is a weak molecular base with Kb = 6. 6 × 10 −^9. What is the pH of a 0. M solution of hydroxylamine?
- pH = 10.
- pH = 7.
- pH = 4.
- pH = 8.
- pH = 9.26 correct
- pH = 9.
- pH = 3.
Explanation: Hydroxylamine is a weak base, so use the equation to calculate weak base [OH−] con- centration (note that this is the approximate equation. Why? Because Kb is very small and the concentration is reasonable) : [OH−] =
Kb Cb
=
(6. 6 × 10 −^9 ) (0.0500)
= 1. 82 × 10 −^5
After finding [OH−], you can find pH using either method below: A) pOH = − log
1. 82 × 10 −^5
pH = 14 − 4 .74 = 9. 26 or B) [H+] =
Kw [OH−]
=
1. 0 × 10 −^14
1. 82 × 10 −^5
= 5. 52 × 10 −^10
pH = − log
5. 52 × 10 −^10
019 (part 1 of 2) 10.0 points
Calculate the pH of the solute in an aque- ous solution of 0.36 M C 5 H 5 N(aq) (pyridine) if the Kb is 1. 8 × 10 −^9.
Correct answer: 9.40579.
Explanation: C◦ pyridine = 0.36 M Kb = 1. 8 × 10 −^9
C 5 H 5 N + H 2 O ⇀↽ C 6 H 5 NH+^ + OH−
−x − +x +x
- 36 − x − x x
Kb =
[C 6 H 5 NH+][OH−]
[C 5 H 5 N]
1. 8 × 10 −^9 =
x^2
- 36 − x
x^2
- 36 x = [OH−] =
0 .36(1. 8 × 10 −^9 )
= 2. 54558 × 10 −^5 mol/L.
1. 1. 8 × 10 −^16
2. 1. 8 × 10 −^9
3. 5. 6 × 108
4. − 1. 8 × 10 −^9
- 6 × 10 −^6 correct
Explanation:
024 10.0 points The pH of 0.010 M aniline(aq) is 8.32. What is the percentage aniline protonated?
- 0.21%
- 2.1%
- 0.12%
- 0.021% correct
- 0.69%
Explanation:
