Chapter 3

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Questions and Answers

Which statement correctly describes the relationship between acids and their conjugate bases?

Stronger acids have stronger conjugate bases.

Weaker acids have stronger conjugate bases.

Stronger acids have weaker conjugate bases. (correct)

Conjugate bases have no relation to acid strength.

What is the implication of a higher pKa value in a conjugate acid?

The acid is neutral.

The acid is stronger.

The conjugate base is weaker.

The conjugate base is stronger. (correct)

In acid-base reactions, which species is favored at equilibrium?

The weaker acid and the weaker base. (correct)

The stronger acid and the stronger base.

The weaker acid and the stronger base.

The stronger acid and the weaker base.

Based on pKa values, which of the following pairs correctly identifies the stronger base?

H2O vs CH3OH (A) Signup and view all the answers

What can be inferred about the water solubility of carboxylic acids with more than five carbon atoms?

Their solubility decreases with carbon count. (B) Signup and view all the answers

Which of the following bases is classified as a strong base based on its comparative pKa value?

HO (B) Signup and view all the answers

Which statement about the solubility of NaOH and amines is correct?

NaOH is soluble in water, but amines with high molecular weights are insoluble. (A) Signup and view all the answers

What trend is observed in the acidity of hydrogen halides as their bond strength changes?

Acidity decreases with increasing bond strength. (A) Signup and view all the answers

Which hydrogen halide has the strongest bond and thus the weakest acid?

HF (A) Signup and view all the answers

Which of the following correctly states the relationship between acidity and molecular structure as we move down a group in the Periodic Table?

Acidity increases, while bond strength decreases. (D) Signup and view all the answers

Which statement about the solubility of amines in aqueous acids is true?

Amines are soluble in aqueous acids because they form salts. (D) Signup and view all the answers

Which of the following represents the correct relationship between electronegativity and charge acquisition of an atom?

Higher electronegativity facilitates the acquisition of a negative charge. (B) Signup and view all the answers

Considering the provided bond lengths and pKa values, which hydrogen halide exhibits the highest pKa, indicating the lowest acidity?

HF (A) Signup and view all the answers

What happens to the acidity of hydrogen halides as their bond lengths increase?

Acidity decreases as bond lengths increase. (C) Signup and view all the answers

Which of the following correctly ranks the hydrogen halides by increasing acidity?

HF < HCl < HBr < HI (A) Signup and view all the answers

What best describes the inductive effect of fluorine on the carbon atom it is bonded to?

It weakens as the distance from the carbon increases. (B), It imparts a greater positive charge to the carbon it is closest to. (C) Signup and view all the answers

When comparing the acidity of acetic acid and ethanol, what is the primary factor for their difference in acidity?

Stability of their conjugate bases. (D) Signup and view all the answers

Which factor contributes to the resonance stabilization of acetate compared to ethoxide?

Delocalization of negative charge across multiple atoms. (A) Signup and view all the answers

Which of the following statements about inductive effects is incorrect?

Inductive effects only occur in polar bonds. (A) Signup and view all the answers

What is a key characteristic of carbocations?

They are electron deficient. (A) Signup and view all the answers

Why is acetic acid a stronger acid than ethanol based on their respective pKa values?

Acetic acid has a lower energy change associated with its dissociation. (A) Signup and view all the answers

An electrophile is defined as a reagent that:

Seeks electrons to achieve electron stability. (D) Signup and view all the answers

Which statement correctly describes carbanions?

They are classified as Lewis bases. (D) Signup and view all the answers

Which statement about the distance and inductive effects is accurate?

Inductive effects are negligible at long distances. (B) Signup and view all the answers

How does the structure of acetic acid contribute to its acidity compared to ethanol?

The carboxylic group in acetic acid stabilizes the conjugate base. (B) Signup and view all the answers

What is the relationship between Lewis acids and electrophiles?

All Lewis acids are electrophiles. (C) Signup and view all the answers

What role does electron delocalization play in the stability of conjugate bases?

It allows for equal sharing of charge among atoms. (D) Signup and view all the answers

What is true regarding the dissociation of bonds in heterolysis?

It requires polarized bonds. (A) Signup and view all the answers

What role do carbocations play in chemical reactions?

They are electron-seeking reagents. (D) Signup and view all the answers

What is the relationship between pKa and acid strength?

Lower pKa values indicate stronger acids. (C) Signup and view all the answers

Which of the following is a true statement regarding the acidity of acetic acid and ethanol?

Acetic acid is a stronger acid than ethanol. (D) Signup and view all the answers

How do carbon atoms, which are electron poor due to bond polarity but are not carbocations, behave?

They behave as electrophiles. (C) Signup and view all the answers

What is the distinguishing feature of a nucleophile?

It seeks a positive center. (C) Signup and view all the answers

What happens during the heterolytic cleavage of a bond?

Only one atom retains both electrons. (B) Signup and view all the answers

What defines a Lewis acid in the context of carbocations?

It accepts an electron pair. (C) Signup and view all the answers

What is the relationship between Ka and the strength of an acid?

A higher Ka indicates a stronger acid. (B) Signup and view all the answers

At 25°C, the acidity constant for acetic acid is given as 1.76 x 10−5. What can be inferred about acetic acid based on this value?

Acetic acid is a weak acid. (B) Signup and view all the answers

What is the equilibrium expression for the dissociation of a generic weak acid HA in water?

Ka = [H3O+][A-]/[HA] (A) Signup and view all the answers

In a 0.1 M solution of acetic acid, approximately what percentage of molecules ionize at 25°C?

1% (D) Signup and view all the answers

What happens to the value of Ka if the concentration of a weak acid in solution is increased?

The value of Ka remains the same. (A) Signup and view all the answers

For which of the following acids would you expect the largest value of Ka?

Hydrochloric acid (HCl) (B) Signup and view all the answers

Which of the following best describes a weak acid?

An acid that partially dissociates in solution. (C) Signup and view all the answers

What is the equivalent expression for the acidity constant (Ka) derived from Keq for a weak acid?

Ka = Keq * [H2O] (B) Signup and view all the answers

Why is acetic acid considered a weak acid compared to strong acids like HCl?

Because it ionizes only slightly in solution. (A) Signup and view all the answers

What characterizes the equilibrium constant (Keq) in the context of weak acid dissociation?

It describes the ratio of products to reactants at equilibrium. (B) Signup and view all the answers

Study Notes

Acidity and Basicity

Carboxylic acids with more than 5 carbons are insoluble in water.
Carboxylic acids become soluble in water due to their polarity when they form salts in reaction with NaOH (sodium hydroxide).
Amines with high molecular weights are also insoluble in water.
Amines are basic and will form salts with aqueous acids.

Structure and Acidity

The strength of the H-X bond determines the strength of the acid. H-F, H-Cl, H-Br, and H-I.
Stronger bond = weaker acid.
Acidity increases going down a group in the periodic table.
Higher electronegativity of an atom makes it easier to acquire a negative charge.
Inductive effects are electronic effects transmitted through the bonds of molecules.
Inductive effects can be electron donating or electron withdrawing.
Strength of inductive effects decrease with distance.

Acidity: Carboxylic Acids vs. Alcohols

Carboxylic acids are more acidic than alcohols.
Acetic acid is more acidic than ethanol.
The pKa value of acetic acid is 4.75.
The pKa value of ethanol is 16.
The stronger the acid, the weaker the conjugate base.

The Effect of Delocalization

The conjugate base of acetate is more stable than the conjugate base of ethoxide due to resonance stabilization.
This resonance stabilization is what makes acetate a stronger acid than ethanol.

The Inductive Effect

The inductive effect is a stabilizing effect in which an electron-withdrawing group like fluorine increases the acidity of a compound.

Heterolysis of Bonds to Carbon: Carbocations and Carbanions

Heterolysis is a type of bond cleavage involving the breaking of a bond where both electrons go to a single atom.
Carbocations are electron-deficient as they have only 6 electrons in their valence shell.
Carbocations are Lewis acids.

Electrophiles and Nucleophiles

Carbocations are electrophiles because they are electron-seeking molecules.
Electrophiles are reagents that seek out electron pairs to achieve a stable octet.
Carbocations are Lewis acids and electrophiles.
Carbanions are Lewis bases.
A nucleophile is a Lewis base that seeks a positive center, such as a positively charged carbon atom.

The Strength of Brønsted-Lowry Acids and Bases

Strong acids such as HCl and H2SO4 fully dissociate in solution while weak acids such as acetic acid only partially dissociate.
Acetic acid is a weak acid with an acidity constant (Ka) of 1.76 x 10^-5.
Acids with large Ka values are strong acids.
Acids with small Ka values are weak acids.
pKa is used to predict the relative strength of bases.
Stronger acids have weaker conjugate bases.
The larger the pKa of a compound the stronger the base.

Predicting the Outcome of Acid-Base Reactions

Acid-base reactions favor the formation of the weaker acid and weaker base.
Acid-base reactions follow equilibrium control.
Reactions following equilibrium control favor the formation of the most stable species (lowest potential energy).
Water solubility is determined by the formation of salts.

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Description

Explore the principles of acidity and basicity with a focus on carboxylic acids and amines. This quiz covers solubility, bond strength, inductive effects, and compares the acidity of different functional groups. Test your understanding of these key chemical concepts.