Table of contents

1. A Review of General Chemistry(0)
2. Molecular Representations(0)
3. Acids and Bases(0)
4. Alkanes and Cycloalkanes(0)
5. Chirality(0)
6. Thermodynamics and Kinetics(0)
7. Substitution Reactions(0)
8. Elimination Reactions(0)
9. Alkenes and Alkynes(0)
10. Addition Reactions(0)
11. Radical Reactions(0)
12. Alcohols, Ethers, Epoxides and Thiols(0)
13. Alcohols and Carbonyl Compounds(0)
14. Synthetic Techniques(0)
15. Analytical Techniques:IR, NMR, Mass Spect(0)
16. Conjugated Systems(0)
17. Ultraviolet Spectroscopy(0)
18. Aromaticity(0)
19. Reactions of Aromatics: EAS and Beyond(0)
20. Phenols(0)
21. Aldehydes and Ketones: Nucleophilic Addition(0)
22. Carboxylic Acid Derivatives: NAS(0)
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides(0)
24. Enolate Chemistry: Reactions at the Alpha-Carbon(0)
25. Condensation Chemistry(0)
26. Amines(0)
27. Heterocycles(0)
28. Carbohydrates(0)
29. Amino Acids(0)
30. Peptides and Proteins(0)
32. Lipids (0)
34. Nucleic Acids(0)
35. Transition Metals(0)

3. Acids and Bases

Ranking Acidity

3. Acids and Bases

Ranking Acidity - Online Tutor, Practice Problems & Exam Prep

Ranking Acidity Practice Problems

127 problems

1PRACTICE PROBLEM

Rank these compounds in order of increasing acidity.

A. CH₃CH₃

B. CH₃OH

C. CH₃NH₂

D. CH₃SH

2PRACTICE PROBLEM

Rank these compounds from the least acidic to the most acidic.

FCH₂COOH, BrCH₂COOH, ClCH₂COOH

3PRACTICE PROBLEM

Rank these compounds in order of increasing acidity.

A. CH₃CH₂CH₂CH₂OH

B. CH₃CH₂CH═CHCH₂OH

C. CH₃CH₂C≡CCH₂OH

4PRACTICE PROBLEM

Predict the most reactive protonation site in each of the following compounds.

5PRACTICE PROBLEM

Determine and rationalize which will have a higher pK_a value between the two hydroxyl groups in the following structure.

6PRACTICE PROBLEM

Identify the stronger acid in each of the following pairs.

7PRACTICE PROBLEM

Identify the anion that would more readily react with H⁺.

8PRACTICE PROBLEM

There are four compounds given in increasing order of acidity. The most acidic hydrogen in each of these structures is circled. Explain why each of these compounds is more acidic than the preceding one.

9PRACTICE PROBLEM

Explain the relative acidities of the following conjugate acids.

10PRACTICE PROBLEM

Arrange the indicated hydrogens in these molecules in decreasing order of acidity.

11PRACTICE PROBLEM

Consider the following acid-base reactions:
I) ClCH₂COOH + Cl₃CCOONa ⇌
II) CH₃CH₂OH + HNO₃ ⇌
III) CH₃OH + H⁻ ⇌
Indicate the conjugate acids and bases in your answers and determine the direction of equilibrium. Try to determine reaction direction without the use of the pKa values. You can find the pKa values on the internet if required.

12PRACTICE PROBLEM

Compare and arrange these compounds in increasing order of acidity. Provide a suitable reason for your answer.
CH₃CH₂OH, HCOOH, HCl, HBr, CH₄, and CH₃CH(Cl)COOH

13PRACTICE PROBLEM

Explain why FCH₂COOH is more acidic than ICH₂COOH if HF is less acidic than HI.

14PRACTICE PROBLEM

Which of the compounds shown below is more acidic?

15PRACTICE PROBLEM

Between H_a and H_b (boxed in the structure), which is expected to have a lower pK_a?

16PRACTICE PROBLEM

Consider the following acid-base reaction and answer these questions:

(a) Which is stronger, the acid or the conjugate acid?

(b) Would the K_eq be less than, equal to, or greater than one?

17PRACTICE PROBLEM

Rank these compounds from the least acidic to the most acidic.

18PRACTICE PROBLEM

What are the product(s) (if a reaction takes place) for the following reactions?

a) Acetic acid + sodium methoxide

b) Phenol + sodium formate

19PRACTICE PROBLEM

Identify the stronger base in each of the pairs given below.

20PRACTICE PROBLEM

(i) Pick out the most stable conjugate base among the following.

(ii) Which structural feature(s) did you analyze?

21PRACTICE PROBLEM

Which of the indicated oxygen atoms is the most basic in the following structures?

22PRACTICE PROBLEM

(i) Identify the stronger acid among the following pair.

(ii) Which structural feature(s) did you analyze?

(Hint: draw the conjugate base first)

23PRACTICE PROBLEM

Which of the following compounds is more acidic? Why?

(Note: The most acidic proton for each compound is encircled.)

24PRACTICE PROBLEM

Arrange the given compounds in increasing order of acidity.

25PRACTICE PROBLEM

Rank the following compounds in increasing order of acidity. Provide reasoning for your answer.

26PRACTICE PROBLEM

Rank these compounds from the least acidic to the most acidic.

27PRACTICE PROBLEM

Identify the substituents in each of the following compounds as inductively electron-withdrawing, electron-donating by hyperconjugation, electron-withdrawing by resonance, or electron-donating by resonance.

a. —Cl

b. —CH₃

c. —CHO

28PRACTICE PROBLEM

Explain the large difference in the p K_a values of acetic acid (pK_a= 4.8) and trifluoroacetic acid (pK_a= 0.2).

29PRACTICE PROBLEM

Why aniline is a stronger acid compared to cyclohexylamine?

30PRACTICE PROBLEM

(i) Identify the most stable conjugate base in the following pair.

(ii) Which structural feature(s) did you analyze?

31PRACTICE PROBLEM

Rank the following compounds in order of decreasing acidity.

32PRACTICE PROBLEM

Imidazole has two nitrogen atoms. Determine which nitrogen is more basic and which one is less basic in its structure.

33PRACTICE PROBLEM

Identify the stronger base in each pair.

34PRACTICE PROBLEM

Explain why the hydroxy proton of kojic acid at carbon-5 is more readily lost than the hydroxy proton at carbon-7.

35PRACTICE PROBLEM

Identify the more basic member among each pair of the compounds given below.

36PRACTICE PROBLEM

Observe the increasing order of acidity of the following compounds.

a. What effect does bromine, an electronegative atom, have on the acidity of a carboxylic acid?

b. How does the substituent position influence the acidity of a carboxylic acid?

37PRACTICE PROBLEM

(i) Pick out the stronger acid among the following.

(ii) Which structural feature(s) you analyzed?

(Hint: draw the conjugate base first)

38PRACTICE PROBLEM

Ammonia (NH₃), methanol (CH₃OH), and propanoic acid (CH₃CH₂COOH) can act as either acids or bases, depending on the conditions.

Arrange the three compounds from the least basic to the most basic. Additionally, write a reaction for each compound reacting with a generic acid (HA).

39PRACTICE PROBLEM

Identify which molecule loses the indicated proton more readily.

40PRACTICE PROBLEM

Rank the following anions in order of increasing basicity.

A. CH₃O⁻

B. Cl⁻

C. CH₃NH⁻

D. CH₃CH₂⁻

41PRACTICE PROBLEM

Identify the stronger acid in each pair.

a. (i) CH₃CH₂OH or (ii) CH₃CH₂NH₂

b. (i) CH₃CH₂OH or (ii) CH₃CH₂SH

42PRACTICE PROBLEM

Why is the conjugate acid of piperazine more acidic than the conjugate acid of piperidine?

43PRACTICE PROBLEM

Consider the following acid-base reaction and answer these questions:

(a) Which is stronger, the base or the conjugate base?

(b) Which side is favored, the reactants or the products?

44PRACTICE PROBLEM

Which one of the given molecules is expected to have a greater K_a? Which one is a stronger acid?

45PRACTICE PROBLEM

Why is the pK_a of the α-hydrogen of N,N-dimethylacetoacetamide higher than the pK_a of the α-hydrogen of ethyl acetoacetate?

46PRACTICE PROBLEM

Consider the following nitrogenous compounds. Rank these compounds in order of increasing basic strength. Use the concept of hybridization. Additionally, rank their conjugate acids in order of decreasing acidic strength.

47PRACTICE PROBLEM

The following molecule has two nitrogen atoms. Determine which of these nitrogens would be protonated preferentially.

48PRACTICE PROBLEM

Identify the stronger acid in each pair.

a. (i) CH₃CH₂CH₂OCH₂CH₂OH or (ii) CH₃CH₂OCH₂CH₂CH₂OH

49PRACTICE PROBLEM

Explain why 2,4-dinitrophenol (pK_a= 4.0) is a stronger acid than 3,5-dinitrophenol (pK_a= 6.7).

50PRACTICE PROBLEM

Identify the stronger acid in each of the following pairs.

51PRACTICE PROBLEM

Rank the following acids from the strongest to the weakest acid. Provide a brief explanation for your answer.

52PRACTICE PROBLEM

Consider the reaction of the given compound with a strong base:

Which labeled proton is expected to be removed first?

53PRACTICE PROBLEM

Identify the following substituents as inductively electron-withdrawing, electron-donating by resonance, electron-withdrawing by resonance, or electron-donating by hyperconjugation.

a. —CH(CH₃)₂

b. —CH₂COOCH₃

c. —OH

54PRACTICE PROBLEM

Rank the following anions in order of increasing basicity.

A. CH₃CH₂CH₂⁻

B. CH₃C≡C⁻

C. CH₃CH=CH⁻

55PRACTICE PROBLEM

Identify the acid that would more readily donate a proton to a base.

56PRACTICE PROBLEM

Ammonia (NH₃), methanol (CH₃OH), and propanoic acid (CH₃CH₂COOH) can act as either acids or bases, depending on the conditions.

Arrange the three compounds from the least acidic to the most acidic. Additionally, write a reaction for each compound reacting with a generic base (B⁻).

57PRACTICE PROBLEM

A negative charge on an adjacent carbon atom can be stabilized by a nitrile group (-CN) through resonance. Of the three hydroxybenzonitrile derivatives shown below, one is only slightly more acidic than phenol, while the other two are much more acidic than phenol. Use resonance structures of the appropriate phenoxide ions to explain why two of the ions are unusually stable.

58PRACTICE PROBLEM

The following diagram shows two pairs of organic bases. For each pair, determine which compound is a stronger base and draw their conjugate acids. Additionally, determine which conjugate acid in a pair is stronger.

59PRACTICE PROBLEM

Rank the following compounds in the order from strongest to weakest acid.

CH₃OH
CCl₃CH₂COOH
CCl₃COOH
CH₃CH₂COOH

60PRACTICE PROBLEM

Predict the most reactive protonation site in each of the following compounds.

61PRACTICE PROBLEM

Identify the stronger base in each pair.

62PRACTICE PROBLEM

Identify the stronger base in each pair.

63PRACTICE PROBLEM

Below are the pK_a values of 2-iodobenzoic acid, 3-iodobenzoic acid, and 4-iodobenzoic acid.

Explain why the ortho-substituted benzoic acid is the most acidic, while the para-substituted is the least acidic.

64PRACTICE PROBLEM

An ascorbic acid derivative is slightly more acidic than propanoic acid, even though the derivative lacks the carboxylic acid group. Compare the conjugate base of propanoic acid with the most stable conjugate base of the ascorbic acid derivative and suggest why these two compounds have similar acidities.

65PRACTICE PROBLEM

Rank the following compounds in order of decreasing acidity.

66PRACTICE PROBLEM

Determine the more acidic molecule in each of the given pairs of isomers. Provide a suitable reason for your answer.

(a)

(b)

67PRACTICE PROBLEM

Protonation can take place on any of the three nitrogen atoms of the following compound. However, one of the three nitrogen atoms is much more basic. Identify the most basic nitrogen atom in the compound.

68PRACTICE PROBLEM

Identify the stronger acid in the given pair.

69PRACTICE PROBLEM

Why is m-methoxyphenol (pK_a = 9.65) more acidic than p-methoxyphenol (pK_a = 10.2)?

70PRACTICE PROBLEM

Which one is the most basic compound in the following pair? Explain why.

71PRACTICE PROBLEM

Discuss the relative acidities of the following alcohols.

(Most acidic) a. CH₃C≡CCH₂OH > b. CH₃CH═CHCH₂OH > c. CH₃CH₂CH₂CH₂OH (Least acidic)

72PRACTICE PROBLEM

Which of the two compounds, HI and HBr, is more acidic?

73PRACTICE PROBLEM

Which of the following compounds is expected to have higher acidity?

74PRACTICE PROBLEM

True or False. The expected order of the pK_a values of the carboxyl groups of aspartic acid, valine, and glycine corresponds to the following.

75PRACTICE PROBLEM

Arrange the following amines in increasing order of their basicity.

76PRACTICE PROBLEM

Guanidine (HNC(NH₂)₂) is an organic base that is used to produce hair relaxers. Draw a conjugate acid for guanidine. Do you anticipate guanidine to be a weak base or a strong base?

77PRACTICE PROBLEM

What prevents the protonation of the encircled nitrogen at physiological pH?

78PRACTICE PROBLEM

Which of the encircled atoms is more basic?

79PRACTICE PROBLEM

Arrange the following alcohols in decreasing order based on their pK_a values. Explain.

80PRACTICE PROBLEM

For the given acid-base reaction:

(i) Is the reactant base or conjugate base stronger?

(ii) Identify the side of the reaction that is favored.

(iii) Is the K_eq less than or greater than 1?

81PRACTICE PROBLEM

Choose the more stable base between the given pair of ions.

82PRACTICE PROBLEM

Identify the stronger base in the pair below. Provide a brief explanation without the pK_a values.

83PRACTICE PROBLEM

The molecule shown below is a heteroatomic base. Which of the two nitrogens is more basic?

84PRACTICE PROBLEM

Consider the following pair:

Without referring to the pK_a values, choose the least reactive base. Explain your answer.

85PRACTICE PROBLEM

Consider the following acid-base reaction:

(i) Is the reactant acid stronger than the conjugate acid?

(ii) Determine which direction of the reaction (forward or reverse) is more favored.

(iii) Will the equilibrium constant (K_eq) be less than, equal to, or greater than 1?

86PRACTICE PROBLEM

Rank the following alkenes in order of decreasing rate of protonation.

Note: Only focus on basicity at the double bonds ignoring any other sites that may be more basic.

87PRACTICE PROBLEM

Which in the given pair of ions would react with H⁺ most quickly?

88PRACTICE PROBLEM

Determine the acid you would expect to donate a proton more readily to a basic compound.

89PRACTICE PROBLEM

Identify the more stable conjugate base in the pair of structures shown below. Which structural feature did you analyze to answer the question?

90PRACTICE PROBLEM

Which is a more stable conjugate base in the following pair of structures? Provide the basis for your answer.

91PRACTICE PROBLEM

(i) Which of the two molecules below has a more acidic proton?

(ii) Which structural feature did you analyze for your answer?

[Hint: Draw the structure of the conjugate bases.]

92PRACTICE PROBLEM

(i) Which has a more acidic proton in the pair of molecules shown below?

(ii) What structural feature did you analyze to answer the question?

[Hint: Start by drawing the conjugate bases.]

93PRACTICE PROBLEM

Choose the more stable base between the given compounds.

H₂O and H₂S

94PRACTICE PROBLEM

Shown below are the structures of drugs and the diseases they treat. Predict whether the activity of these drugs will increase, decrease, or not be affected when taken with medicine for acid reflux diseases.

95PRACTICE PROBLEM

Provide an explanation for the following: A base can deprotonate the α-carbon of methyl propionate but not the α-carbons of propionic acid and propionamide.

96PRACTICE PROBLEM

Arrange compounds X, Y, and Z in order of decreasing ease of proton removal from the methyl substituent.

97PRACTICE PROBLEM

Malic acid is a compound with two —COOH groups. Why is its first pK_a lower than the pK_a of acetic acid? (The first pK_a of malic acid is for the —COOH group adjacent to the —OH group.)

98PRACTICE PROBLEM

One of the given four amino acid side chains can deprotonate the ɑ-carbon of an aldehyde. Which one is it?

99PRACTICE PROBLEM

Explain why the pK_a of 2,2,2-trifluoroethanol (12.4) is lower than the pK_a of ethanol (16.0).

100PRACTICE PROBLEM

The structure shown below has four possible acidic groups. (Note that phosphorus is a period 3 element, hence it can expand its octet and have more than four bonds.)

(i) Which group is the strongest acid? Justify your answer.

(ii) Which group is the weakest acid?

101PRACTICE PROBLEM

Consider the following compounds:

Explain the relative acidities.

102PRACTICE PROBLEM

Are the pK_a values of alanylalanine expected to be higher or lower than the pK_a values of alanine (pK_a1 = 2.34 and pK_a2 = 9.69)?

103PRACTICE PROBLEM

Which of the following statements is true?

(i) The 4-methylbenzenaminium ion has a greater K_a than the 4-methylcyclohexan-1-aminium ion.

(ii) 4-methylcyclohexan-1-amine is a stronger base than p-toluidine.

104PRACTICE PROBLEM

True or False: When 1,3-dimethylguanidine is protonated, its double-bonded nitrogen is the nitrogen that accepts the proton because the lone pair electrons on the other nitrogens are delocalized.

105PRACTICE PROBLEM

Determine which among the given molecules is the strongest base.

106PRACTICE PROBLEM

The pK_a values of ortho-, meta-, and para-methoxybenzoic acids are shown below:

The relative pK_a values depend on the substituent. The ortho isomer is the most acidic, and the para isomer is the least acidic. Explain these relative acidities.

107PRACTICE PROBLEM

Examine the compounds below with their pK_a values. Show the conjugate base of each compound and rationalize why the acidity increases with increasing nitro substituents.

(i) CH₃CH₃, pK_a ≈ 50

(ii) CH₃CH₂NO₂, pK_a = 8.98

(iii) CH₃CH(NO₂)₂, pK_a = 5.50

108PRACTICE PROBLEM

Identify the more acidic isomer and illustrate why it is more acidic by removing a proton at the indicated atom and showing resonance forms (if applicable)

109PRACTICE PROBLEM

Identify the more acidic member of each pair and illustrate why it is more acidic by removing a proton at the indicated atom and showing resonance forms (if applicable).

110PRACTICE PROBLEM

Consider the molecule shown below:

(i) Draw the four different conjugate bases that can be formed assuming each OH group can be deprotonated.

(ii) Identify the most acidic OH group in the molecule.

111PRACTICE PROBLEM

Between each pair, which is more basic? Explain.

112PRACTICE PROBLEM

Choose the more basic of the two structures below. Why?

113PRACTICE PROBLEM

Rank the conjugate acids of the following bases from the most stable to the least stable.

(i) NH₃, (ii) CH₃CH₂CH₂OH, (iii) KOH, (iv) CH₃CH₂CONH₂

114PRACTICE PROBLEM

Consider the listed properties of ethanol and 2,2,2-trifluoroethanol below and answer the following questions.

(i) Compound 2 has a molecular weight that is more than twice that of compound 1, but compound 2 has a slightly lower boiling point. Why?

(ii) Despite three electronegative fluorine atoms, the dipole moment of compound 2 is lower than that of compound 1. Explain why.

(iii) Compound 2 is a stronger acid than compound 1. Why is this the case?

115PRACTICE PROBLEM

A pair of compounds is shown below. When treated with a base, compound (b) reacts more quickly than compound (a). Explain the enhanced acidity of compound (b) compared to compound (a).

116PRACTICE PROBLEM

Explain, using the resonance forms of the conjugate bases, why benzenesulfonic acid (C₆H₅SO₃H) exhibits a higher acidity than benzoic acid (C₆H₅COOH).

<IMAGE>

117PRACTICE PROBLEM

Predict the structure of the anion formed by the abstraction of a proton from the following compound using NaOH. Also, draw the important resonance forms involved in the stabilization of this anion.

118PRACTICE PROBLEM

Determine the stronger base between (i) and (ii). Rationalize your choice using the concept of element effect.

119PRACTICE PROBLEM

Choose the stronger base between 1 and 2. Justify your choice without the use of p K_a values.

120PRACTICE PROBLEM

Choose the stronger acid between cyclohexylmethanol and cyclomethanethiol. Explain your answer in terms of element effects.

121PRACTICE PROBLEM

Without knowing the pK_a values, identify the least basic structure among the given pair. Justify your choice.

122PRACTICE PROBLEM

Without knowing the pK_a values of the following structures, identify the least reactive base among them. Justify your choice.

123PRACTICE PROBLEM

Which of these anions is more basic?

F⁻or I⁻

124PRACTICE PROBLEM

Without knowing the pK_a values, identify the more acidic member among the following pair. Justify your choice.

125PRACTICE PROBLEM

Without knowing the pK_a values of the following structures, identify the more reactive base among them. Justify your choice.

126PRACTICE PROBLEM

4-(3-(cyclopentylamino)-2-hydroxypropoxy)benzamide is an analog of a beta-blocker that is used to treat high blood pressure. Which nitrogen atom in 4-(3-(cyclopentylamino)-2-hydroxypropoxy) is the most basic?