AP Chemistry Unit 8- Homework Problems Ka and Kb Acid & Base ...
AP Chemistry Unit 8- Homework Problems Ka and Kb Acid & Base ...
AP Chemistry Unit 8- Homework Problems Ka and Kb Acid & Base ...
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Buffers<br />
1. What is the definition of a buffer?<br />
2. What kind of an acid <strong>and</strong> base are present in a buffer?<br />
3. The K a of carbonic acid is 4.3x10 -7 .<br />
a. What is the pH of a solution that is 0.25 M H 2 CO 3 <strong>and</strong> 0.25 M NaHCO 3 ?<br />
b. What would the ratio of acid to base be if you wanted to buffer at exactly a pH of 6?<br />
4. The K a of hydrozoic acid is 1.9x10 -5 .<br />
a. What is the pH of a solution that is 0.75 M HN 3 <strong>and</strong> 0.75 M N 3 -1 ?<br />
b. What would the ratio of acid to base be if you want to buffer exactly at a pH of 5?<br />
5. The K b of aniline is 4.3x10 -10 .<br />
a. What is the pH of a solution that is 0.050 M C 6 H 5 NH 2 <strong>and</strong> 0.050 M C 6 H 5 NH 3 +1 ?<br />
b. What would the ratio of acid to base be if you want to buffer exactly at a pH of 9?<br />
6. The K b of pyridine is 2x10 -9 .<br />
a. What is the pH of a solution that is 1.25 M C 5 H 5 N <strong>and</strong> 1.25 M C 5 H 5 NH +1 ?<br />
b. What would the ratio of acid to base be if you want to buffer exactly at a pH of 9?<br />
7. Which of the following buffer systems would you choose if you want to buffer at a pH of 2?<br />
-1<br />
a. HC 3 H 5 O 2 / C 3 H 5 O 2 K a = 1.35x10 -5<br />
-1<br />
b. HNO 2 / NO 2 K a = 7.2x10 -4<br />
c. HIO / IO -1 K a = 2.3x10 -11<br />
-1<br />
d. H 3 PO 4 / H 2 PO 4 K a = 7.6x10 -3<br />
Describe how to make the buffer so it is exactly at a pH of 2.<br />
8. Lactic acid has a K a of 8.3x10 -4 . A buffer is made so that it is 0.50 M in HC 3 H 5 O 3 <strong>and</strong> 0.50<br />
M in C 3 H 5 O 3 -1 .<br />
a. What is the pH of the buffer?<br />
b. What will the pH of the buffer be if 0.15 M of HCl are added?<br />
9. Arsenous acid has a K a of 6.6x10 -10 . A solution is made so that it is 50 mL of 1.2 M in<br />
HAsO 2 .<br />
a. What is the pH of the solution?<br />
b. How many grams of NaAsO 2 must be added so the solution is a buffer at a pH of 10?<br />
Assume no change in volume.<br />
10. Methylamine has a K b of 4.2x10 -4 . A buffer is made so that it is 0.75 M in CH 3 NH 2 <strong>and</strong><br />
0.75 M in CH 3 NH 3 +1 .<br />
a. What is the pH of the buffer?<br />
b. What will the pH of the buffer be if 0.25 M of HNO 3 are added?<br />
11. Quinoline has a K b of 6.3x10 -10 . A solution is made so that it is 250 mL of 1.75 M C 9 H 7 N.<br />
a. What is the pH of the solution?<br />
b. How many grams of C 9 H 7 NHCl must be added so that the solution is a buffer exactly<br />
at a pH of 5? Assume no change in volume.
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