CHAPTER 2: ACIDS AND BASES

Which of the following Bronsted-Lowry acid/base classifications are correct?

- (CH3)3N is a base. - CH3COOH is an acid.

Which of the following species are common negatively charged strong bases?

- -H - -NH2 - -OH

Which of the following are commonly used as bases in organic reactions?

- -OH and its organic derivatives - lithium diisopropylamide - butyllithium - triethylamine

Which of the following statements correctly describe Bronsted-Lowry acids?

- A Bronsted-Lowry acid must contain a H atom. - A Bronsted-Lowry acid is a proton donor.

Select all statements that accurately describe Bronsted-Lowry acid-base reactions.

- Acid-base reactions are also known as proton transfer reactions. - One bond is formed in an acid-base reaction.

Which of the following statements correctly describe periodic trends in the acidity of an acid with the general formula HA?

- Acidity of HA increases as atom A moves down a group. - Acidity of HA increases as atom A moves from left to right across a period.

Which of the following species commonly act as Lewis acids in organic reactions?

- AlCl3 - BF3

Which of the statements below correctly describe the curved arrows required to show the mechanism of the following acid-base reaction correctly?

- An arrow must begin on the lone pair of the acetylide and end on a hydrogen of H2O. - An arrow must begin on one of the bonds between H and O and end on O.

Select all species in the diagram that can function as Bronsted-Lowry bases.

- B - C - D *Reason: the base must contain an "available" electron pair that can be easily donated to form a new bond.

Which of the following acids have a conjugate base stabilized by resonance?

- CH3CH2CN - ClCH2COOH

Match the name and/or formula for each compound with its correct description as a common acid or base used in organic chemistry. - strong inorganic acid: - strong organic acid: - weak organic base: - strong organic base:

- HCl - p-toluenesulfonic acid (TsOH) - pyridine - CH3CH2CH2CH2-Li+ (butyllithium)

Which statement(s) correctly describe(s) aspirin, and the proton transfer reaction that converts aspirin to its conjugate base (shown)?

- If NaOH was used as the base, then the ionic form of aspirin would be favored at equilibrium. *Reason: Correct. The conjugate acid of NaOH is H2O, which has a pKa of 15.7 whereas the pKa of aspirin (i.e., a carboxylic acid) is around 5. The right side of the reaction would be favored. - Aspirin is a weak acid. *Reason: Correct. Aspirin is a carboxylic acid, which has an approximate pKa value of 5. Any acid with a pKa value greater than zero is defined as a weak acid.

Select all statements that correctly describe the acid-base chemistry of aspirin and its biological implications.

- In the basic environment of the small intestine, aspirin is deprotonated to form its conjugate base. - Aspirin contains a carboxylic acid functional group.

Which of the following statements correctly describe the inductive effect?

- Inductive effects operate through σ bonds. - This effect is the result of electronegativity differences between atoms.

Match the type of acid with the appropriate Ka value. - Strong acid: - Weak acid:

- Large value of Ka - Small value of Ka

Match each compound with the correct description of its behavior as an acid. - BF3: - H2O:

- Lewis acid - Lewis and Bronsted-Lowry acid

Select all statements that correctly describe Lewis and Bronsted-Lowry acids and bases.

- Not all Lewis acids are Bronsted-Lowry acids. - All Bronsted-Lowry acids are Lewis acids.

A Bronsted-Lowry base must have an "available" electron pair to form a bond to H+. Which of the following structural features allow an electron pair to be used in this way?

- One or more electron pairs in π bonds. - One or more lone pairs in the structure.

Which of the following statements correctly describe the steps involved in any general reaction between a Bronsted-Lowry acid and base (see the diagram)?

- The acid (H-A) loses a proton, leaving an electron pair on atom A. - The electron pair of the base (B:) forms a new bond to H.

Which of the following statements correctly describe the relationship between acids and bases and their conjugates?

- There exists an inverse relationship between acid strength and conjugate base strength. - A strong acid generally forms a weak conjugate base.

In an acid-base reaction, the equilibrium always favors the formation of what species?

- Weak bases - Weak acids *Reason: Equilibrium always favors the formation of the weaker acid and base.

The compound CH3CH2OH (ethanol) can act as either an acid or a base. Match each structure given according to its relationship to ethanol. - CH3CH2O- : - CH3CH2OH2+ :

- conjugate base - conjugate acid

Match each Lewis acid/base term with the correct definition. - Lewis base - Lewis acid

- electron pair donor - electron pair acceptor

Match each term with the correct definition. - electrophile: - nucleophile:

- electron-poor species - electron-rich species

Match the appropriate acid-base process with the correct result. - loss of a proton from an acid: - gain of a proton by a base:

- formation of its conjugate base - formation of its conjugate acid

Match the correct name with the appropriate negatively charged strong base. - OH- - NH2- - H-

- hydroxide - amide - hydride

The name of the compound shown is ______ acid, which is often abbreviated as ______.

- p-Toluenesulfonic acid - TsOH

Match each term with the correct Bronsted-Lowry definition. - Acid: - Base:

- proton (H+) donor - proton (H+) acceptor

Match each substance to its correct description according to each system of defining acids and bases. - Bronsted-Lowry acid: - Bronsted-Lowry base: - Lewis acid: - Lewis base:

- proton donor - proton acceptor - electron pair acceptor - electron pair donor

Match the appropriate values of Ka and pKa. - large Ka: - small Ka:

- small pKa - large pKa

The mathematical relationship between Ka and pKa is expressed as pKa = ______ Ka. When the Ka value is large, the pKa value will be ______.

-log; small

Without using a Ka or pKa table, rank the three compounds shown based on increasing acidity. Place the least acidic molecule at the top of the list.

1. A 2. C 3. B

Without using a Ka or pKa table, rank the three compounds shown based on decreasing acidity. Place the most acidic molecule at the top of the list.

1. C 2. B 3. A

Rank the following compounds in order of increasing acid strength. Place the weakest acid at the top of the list and the strongest acid at the bottom of the list.

1. CH3CH2CH3, pKa= 50 2. CH3CH2OH, pKa= 16 3. Phenol, pKa= 10 *Reason: the smaller the number, the stronger the acid.

Consider a conjugate base of the general formula A-. Rank the conjugate base in order of decreasing stability in terms of the hybrid orbital in which the lone pair of A- is located. Place the most stable situation at the top of the list and the least stable situation at the bottom of the list.

1. sp 2. sp2 3. sp3

According to the Bronsted-Lowry definition, an acid must contain which of the following?

A hydrogen atom

Which of the following conjugate bases are stabilized by resonance?

A; C

Which of the following structural characteristics is required for a compound to act as a Bronsted-Lowry base?

An available electron pair

Which of the following Bronsted-Lowry acid-base reactions is drawn correctly?

C

Which of the following is the correct formula for the conjugate acid of CH3NH2?

CH3NH3+ *Reason: The N atom should be positively charged when CH3NH2 gains an H+.

Which of the following statements correctly describes a general trend observed in organic reactions?

Electron-rich species react with electron-deficient species.

The structure of p-toluenesulfonic acid most closly resembles the structure of _____.

H2SO4 - Reason: Correct. Both sulfuric acid and p-toluenesulfonic acid possess a strongly acidic -SO3H group.

When comparing the acidity of two acids (for example, H-A and H-B), which of the following should be considered FIRST?

The acidity of H-A and H-B based on the location of A and B in the periodic table. *Reason: The most important factor determining the acidity of an acid H-A is the location of A in the periodic table.

Which of the following statements describes a Lewis acid-base reaction correctly?

The base donates an electron pair to the acid.

Which of the following statements correctly describes the process that occurs in a Lewis acid-base reaction?

The base uses its electron pair to form a new covalent bond to the acid.

Which of the following is the MOST important factor that determines the acidity of an H-A bond?

The location of element A in the periodic table

Which of the following correctly describes the term "acid strength"?

The tendency of an acid to donate a proton.

A Lewis acid is an electron pair _____, while a Lewis base is an electron pair _____.

acceptor; donor

According to the Bronsted-Lowry definition, a base is a proton _____, while an acid is a proton _____.

acceptor; donor

When identifying Bronsted-Lowry acids and bases in an organic reaction, if only one species has a lone pair or π bond it must be the _____, while if only one species contains an available hydrogen atom it must be the _____.

base, acid *Reason: A species with a lone pair can readily accept a proton and is therefore defined as a base.

A Bronsted-Lowry acid donates a proton to form its conjugate _____, whereas a Bronsted-Lowry base accepts a proton to form its conjugate _____.

base; acid

In a Lewis acid-base reaction, the base _____ an electron pair to/from the acid. This is an example of a general reaction trend, i.e., that electron-rich species react with electron-_____ species.

donates, deficient

In a Lewis acid-base reaction, the base donates a(n) ______ pair to form a new ______ bond between the base and the acid.

electron; covalent

Acid strength is ______ by any factor that makes the conjugate base more stable.

increased *Reason: If the conjugate base is more stable it will form more readily, making the acid stronger. The more stable the conjugate base, the stronger the acid.

The acidity of acid H-A ______ as atom A moves from left to right across a period and ______ down a group in the periodic table.

increases; increases

For a base of formula A:-, as the s character of the orbital containing the lone pair increases, the stability of the base _____ and the strength of its conjugate acid HA _____.

increases; increases *Reason: If the s character of the orbital increases, the lone pair will be closer to the nucleus and lower in energy. The base will be more stable.

The pull of electron density through σ bonds is called the ______ effect and is caused by a difference in the ______ of the atoms involved.

inductive; electronegativity

A species that is nucleus loving is known as a ______ whereas a compound that is electron loving is known as an ______.

nucleophile; electrophile

In many acid-base reactions a starting material with a net _____ charge is usually an acid while a starting material with a net _____ charge is often a base.

positive; negative

In a proton transfer reaction, equilibrium will favor the _____ if the reacting acid and base are strong. Since a strong acid and base form a _____ conjugate acid and base, the reaction will favor the formation of the _____ acid and base.

products, weak, weaker *Reason: Equilibrium always favors the formation of the weaker acid and base.

Acid strength is a measure of how readily a compound donates a(n) ______.

proton

Acid-base reactions exemplify a general trend of reactivity. The base is an electron-_____ species that reacts readily with the electron-_____ acid.

rich, deficient *Reason: The electron-rich base donates electrons to the acid, which is electron-deficient.

An acid ionizes in aqueous solution according to the equation HA + H2O ⇄ A- + H3O+. A large value for Ka indicates that the equilibrium lies far to the _____ and implies that the acid is ______.

right, strong *Reason: A large value for Ka indicates a strong acid. The equilibrium lies far to the right.

A _____ acid is one that readily donates a proton. Its conjugate base will be _____ ready to accept a proton and will therefore be a relatively _____ base.

strong; less; weak *Reason: The conjugate base will be less ready to accept a proton.

A strong acid has a relatively _____ conjugate base that forms readily and is therefore _____ stable than the conjugate base of a weak acid. Anything that _____ the stability of a conjugate base makes the starting acid more acidic.

weak, more, increases *Reason: A strong acid has a stable conjugate base, which is therefore a weak base. Any factor that increases the stability of the conjugate base makes the acid more acidic.

Acetic acid CH3COOH has a pKa value of 4.8, while fluoroacetic acid CH2FCOOH has a pKa value of 2.6. Acetic acid is a ______ acid than fluoroacetic acid.

weaker *Reason: The smaller the pKa, the stronger the acid.