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CHM 331 > Quiz 3 > Flashcards

Quiz 3 Flashcards

1
Q

Identify the compound with the highest pKa.

A) CH3CH3

B) HCCH

C) CH2CH2

D) CH3OH

E) CH3NH2

A

A) CH3CH3

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2
Q

Which of the following is the strongest acid?

A) CH3OH

B) CH3OH2+

C) H2N-

D) CH3NH2

E) CH3NH3+

A

B) CH3OH2+

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3
Q

The pKa of CH3COOH is 4.8. If the pH of an aqueous solution of CH3COOH and CH3COO- is 4.8, then one knows ________.

A) CH3COOH is completely ionized

B) [CH3COOH] > [CH3COO-]

C) [CH3COOH] = [CH3COO-]

D) [CH3COOH] < [CH3COO-]

E) CH3COOH is completely unionized

A

C) [CH3COOH] = [CH3COO-]

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4
Q

Write a completed equation for the acid-base pair shown below.

HCO2H + -NH2 →

A

HCO2H + -NH2 → HCO2- + NH3

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5
Q

At what pH will the concentration of a compound with a pKa of 5.7 be 100 times greater in its acidic form than in its basic form?

A

3.7

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6
Q

Explain why : NF3 is a weaker base than : NH3.

A

Fluorine has an electron withdrawing effect that reduces the availability of the pair of electrons on nitrogen. Thus the basicity of : NF3 is less than that of : NH3.

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7
Q

If H2O has a pKa value of 15.7 and HF has a pKa value of 3.2, which is a stronger base, HO- or F-? Explain.

A

HO- is a stronger base than F- because HF is a stronger acid than H2O, and the stronger the acid the weaker its conjugate base.

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8
Q

Which of the following is the strongest acid?

A) HF

B) H2O

C) : NH3

D) CH4

E) CH3OH

A

A) HF

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9
Q

When a small amount of hexanoic acid [CH3(CH2)4CO2H, pKa~4.8], is added to a separatory funnel which contains the organic solvent diethyl ether and water with a pH of 12.0, it is found mainly in the ________ phase as ________.

A) ether; CH3(CH2)4CO2-

B) water; CH3(CH2)4CO2-

C) ether; CH3(CH2)4CO2H

D) water; CH3(CH2)4CO2H

E) none of the above

A

B) water; CH3(CH2)4CO2-

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10
Q

The amino acid glycine (H3N+CH2CO2H) has two acidic Hs, one with pKa = 2.34 and the other with pKa=9.60. Draw the structure of the form of glycine that predominates at a pH of 12.

A
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11
Q

At what pH will 25% of a compound with a pKa of 5.3 be in its basic form?

A

4.8

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12
Q

Which of the following is not a conjugate acid-base pair?

A) H2O, HO-

B) H2O, H3O+

C) HSO4-, H2SO4

D) -OH, O2-

E) NO3-, NO2-

A

E) NO3-, NO2-

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13
Q

When a small amount of hexanoic acid [CH3(CH2)4CO2H, pKa~4.8], is added to a separatory funnel which contains the organic solvent diethyl ether and water with a pH of 2.0, it is found mainly in the ________ phase as ________.

A) ether; CH3(CH2)4CO2-

B) water; CH3(CH2)4CO2-

C) ether; CH3(CH2)4CO2H

D) water; CH3(CH2)4CO2H

E) none of the above

A

C) ether; CH3(CH2)4CO2H

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14
Q

HCN has a pKa = 9.1. What form of the compound, HCN or CN-, will predominate in a solution of pH = 7.0

A

HCN

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15
Q
A

A) CH3CH2OH

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16
Q

H-A is an acid with a pKa of 4.5. Which of the following statements about an aqueous solution of H-A is true?

A) At pH = 4.5, the solution contains much more H-A than A-

B) At pH = 4.5, the solution contains much more A- than H-A

C) At pH- 3.5, the solution contains about 90% A- and 10% H-A

D) At pH = 6.5, the soluton contains about 80% A- and 20% H-A

E) At pH = 5.5, the solution contains about 90% A- and 10% H-A

A

E) At pH = 5.5, the solution contains about 90% A- and 10% H-A

17
Q

2-Propanol is shown below. Draw the structure of its conjugate base.

(CH3)2CHOH

A
18
Q

Give the conjugate acid and the conjugate base for HSO4-.

A

Answer: conjugate acid: H2SO4

conjugate base: SO42-

19
Q

Explain why AlCl3 is a Lewis acid.

A

A Lewis acid is an electron pair acceptor. Aluminum in AlCl3 has an empty p orbital that can accommodate the pair of electrons provided by a Lewis base.

20
Q
A

E) V

21
Q

Identify the most acidic carboxylic acid.

A) ICH2COOH

B) BrCH2COOH

C) CH3COOH

D) FCH2COOH

E) ClCH2COOH

A

D) FCH2COOH

22
Q

What is the conjugate base of CH3NH2?

A) CH3NH3+

B) CH3NH-

C) NH4+

D) NH2-

A

B) CH3NH-

23
Q

What is the conjugate acid of NH3?

A) +NH3

B) -NH

C) +NH4

D) -NH2

E) +NH2

A

C) +NH4

24
Q

What is the conjugate acid of CH3NH2?

A) CH3NH3+

B) CH3NH-

C) NH4+

D) NH2-

A

A) CH3NH3+

25
Q

Draw a resonance contributor and the resonance hybrid for HOCO2

A
26
Q

Propanoic acid, CH3CH2COOH, has a pKa =4.9. Draw the structure of the conjugate base of propanoic acid and give the pH above which 90% of the compound will be in this conjugate base form.

A

CH3CH2COO-; 5.9

27
Q
A

A) CH3O- + +NH4

28
Q

The pKa of CH3COOH is 4.8 and the pKa of HCOOH is 3.8. Given this information, one knows that ________.

A) CH3COOH completely ionizes in water

B) HCOOH is a weaker acid than CH3COOH

C) HCOO- is a weaker base than CH3COO-

D) CH3COOH reacts with HO- while HCOOH does not

E) HCOOH reacts with HO- while CH3COOH does not

A

C) HCOO- is a weaker base than CH3COO-

29
Q

Identify the compound with the highest pKa.

A) CH3NH2

B) CH3OH

C) CH3COOH

D) H2O

E) CH3NH3+

A

A) CH3NH2

30
Q

Consider the set of compounds, NH3, HF, and H2O. Rank these compounds in order of increasing acidity and discuss your rationale.

A

NH3 < H2O < HF

31
Q

Which of the following anions, CH3CHBrCO2- or CH3CHFCO2- is the stronger base? Explain your choice

A

CH3CHBrCO2- is the stronger base. The more electronegative F atom can more effectively delocalize the negative charge via induction. This greater delocalization stabilizes CH3CHFCO2- relative to CH3CHBrCO2- and makes it a weaker base.

32
Q
A

C) 2 and 4

33
Q

Buffering is used to maintain the pH of human blood in the relatively narrow 7.3 - 7.4 range. What acid/base pair serves to buffer the blood?

A) H2O / HO-

B) H3O+ / H2O

C) H2CO3 / HCO3-

D) NH4+ / NH3

E) HCl / Cl-

A

C) H2CO3 / HCO3-

34
Q

Would you predict trifluoromethanesulfonic acid, CF3SO3H, to be a stronger or weaker acid than methanesulfonic acid, CH3SO3H? Explain your reasoning.

A

Trifluoromethanesulfonic acid is a stronger acid. Compare the strengths of the conjugate bases and remember that the weaker the base, the stronger the conjugate acid. In the case of the trifluoro derivative, the presence of the highly electronegative fluorine atoms serves to delocalize the negative charge to a greater extent. This additional delocalization makes trifluoromethanesulfonate a weaker base.

35
Q

What is the pH of a 0.1 M solution of HCl? (Note: pKa for HCl is -6.)

A) 6

B) -6

C) 1

D) -8

E) -1

A

C) 1

36
Q

3) The conjugate acid of H2O is ________.

A) H3O-

B) H3O

C) H3O+

D) HO-

E) H2O+

A

C) H3O+

37
Q

4) Which of the following ions is the strongest acid?

A) H-

B) HO-

C) HSO4-

D) H2O

E) H3O+

A

E) H3O+

CHM 331 (9 decks)

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