Ranking Acidity Practice Problems

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

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

CH₃OH
CCl₃CH₂COOH
CCl₃COOH
CH₃CH₂COOH

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.

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

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

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?

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.

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).

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⁻).

Arrange the given compounds in increasing order of acidity.

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

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

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

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

Arrange the following amines in increasing order of their basicity.

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

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

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?

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

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?

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

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

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

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

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

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

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

(Hint: draw the conjugate base first)

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

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

(Hint: draw the conjugate base first)

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

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

Identify the stronger acid in each pair.

a. (i) CH₃CH₂CH₂OCH₂CH₂OH or (ii) CH₃CH₂OCH₂CH₂CH₂OH 

b. 

Identify the stronger base in each pair.

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

Rank these compounds in order of increasing acidity.

A. CH₃CH₃

B. CH₃OH

C. CH₃NH₂

D. CH₃SH

Rank these compounds in order of increasing acidity.

A. CH₃CH₂CH₂CH₂OH

B. CH₃CH₂CH═CHCH₂OH

C. CH₃CH₂C≡CCH₂OH

Rank the following anions in order of increasing basicity.

A. CH₃O⁻ 

B. Cl⁻

C. CH₃NH⁻

D. CH₃CH₂⁻

Identify the stronger base in each pair.

Identify the stronger base in each pair.

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

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

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

Rank the following compounds in order of decreasing acidity.

Rank the following compounds in order of decreasing acidity.

Identify which molecule loses the indicated proton more readily.

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

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

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?

Why aniline is a stronger acid compared to cyclohexylamine?

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

Discuss the relative acidities of the following alcohols.

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

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

Identify the stronger acid in each of the following pairs.

Explain the relative acidities of the following conjugate acids.

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

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. 

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?

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

Rank the following anions in order of increasing basicity.

A. CH₃CH₂CH₂⁻

B. CH₃C≡C⁻

C. CH₃CH=CH⁻

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.

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

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

Identify the stronger acid in the given pair.

Identify the stronger acid in each pair.

a. (i) CH₃CH₂OH or (ii) CH₃CH₂NH₂

b. (i) CH₃CH₂OH or (ii) CH₃CH₂SH

Identify the stronger acid in each of the following pairs.

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.

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.

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

(a)      
                                                         

    (b)

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.

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

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.

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.

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

FCH₂COOH, BrCH₂COOH, ClCH₂COOH

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

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

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

a) Acetic acid + sodium methoxide

b) Phenol + sodium formate