Acid Base Chemistry and Buffers Concept Test

Problem 1

A comic book villain is holding you at gun point and is making you drink a sample of acid. She gives you a beaker with 100ml of a strong acid with pH=5. She also gives you a beaker of a strong base with a pH=10. You can add as much of the strong base to the strong acid as you want, and you must then drink the solution. You'd be best off trying to make the solution neutral before drinking it. How much of the base should you add?

  1. 1 ml
  2. 10 ml
  3. 100 ml
  4. 1000 ml

Problem 2

Consider an exceptionally weak acid, HA, with a Ka = 1x10 -20 . You make a 0.1M solution of the salt Na

  1. What is the pH?
  2. 1
  3. 2
  4. 12
  5. 13

Problem 3

You have a powder that dissolves in water to form a strong acid. You dissolve 2g of the powder in 100ml of water, and measure the pH to be 4. You would like to form 100ml of a solution with pH 5. How many grams of the powder do you dissolve in 100ml of water?

  1. 0.2 g
  2. 0.4 g
  3. 20 g
  4. 40 g

Problem 4

You have two solutions, both with a concentration of 0.1M. Solution A contains a weak acid with a pKa of 5. ThepH of solution A is 3. Solution B contains a weak acid with a pKa of 9. The pH of solution B is:

  1. 1
  2. 2
  3. 4
  4. 5

Problem 5

You have 50 ml of a complex mixture of weak acids that contains some HF (pKa = 3.18) and some HCN (pKa = 9.21). Which is larger, [F-]/[HF] or [CN-]/[HCN]?

  1. [F-]/[HF]
  2. [CN-]/[HCN]
  3. can.t tell from available information

Problem 6

A mixture of 50ml of 0.1M HCOOH and 50ml of 0.05M NaOH is equivalent to:

  1. a 0.05M solution of NaCOOH
  2. a 0.025M solution of NaCOOH
  3. a solution that is 0.05M in HCOOH and 0.05M in NaCOOH
  4. a solution that is 0.025M in HCOOH and 0.025M in NaCOOH

Problem 7

I want to make a solution that will have [HCOO - ] = 3[HCOOH]. I start with 100ml of a 0.1M HCOOH solution. How many ml of a 1M KOH solution should I add?

  1. 5ml
  2. 7.5ml
  3. 25ml
  4. 75ml

Problem 8

Which do you think is a better buffer (more resistant to addition of acid and base)?

  1. a solution that is 0.1M in HA and 0.01M in A
  2. a solution that is 0.01M in HA and 0.1M in A
  3. a solution that is 0.1M in HA and 0.1M in A
  4. a solution that is 0.05M in HA and 0.05M in A

Problem 9

Consider a protein with the acidic side chains,

Amino Acid side-chain Arginine pKa = 12.48
Aspartic Acid PKa = 3.90
Cysteine pKa = 8.33
Glutamic acid pKa = 4.07
Histidine pKa = 6.04
Lysine pKa =10.79
Tyrosine pKa =10.13
Given that the pH of blood is about 7.3, how many of the above side chains would be mostly in their ionic form (A-) in blood?

  1. 2
  2. 3
  3. 4
  4. 5

Problem 10

You are titrating an acid with a pKa of 7. You are given a choice of indicators with the following pKa's, which do you use?

  1. 3
  2. 5
  3. 7
  4. 9

Problem 11

CO2 dissolves in water to form carbonic acid: H2CO3 <---> H+ + HCO3-Ka1 = 4.3 x l0-7 HCO3 <---> H+ + CO3-2 Ka2 = 4.8 x l0-11 In an acid solution with pH =4.35 ([H+ ]=4.5x10-5), what is the ratio [CO3-2] /[H2CO3]?

  1. 10-2
  2. 10-4
  3. 10-6
  4. 10-8