Chapter 2 Flashcards
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-
Answer: E
What is the product formed from the following acid-base reaction when ammonia functions as a base? The equilibrium lies far to the reactants.
A) CH3O- + +NH4
B) CH2OH + +NH3
C) CH3OH2+ + -NH2
D) CH3NH2 + H2O
E) CH4 + NH2OH
Answer: A
The conjugate acid of H2O is
A) H3O-.
B) H3O.
C) H3O+.
D) HO-.
E) H2O+.
Answer: C
Which of the following ions is the strongest acid?
Which of the following ions is the strongest acid?
A) H-
B)HO- -
C) HSO4
D) H2O
E) H3O+
Answer: E
Which species act as bases in the following reaction?
A) 1 and 2
B) 3 and 4
C) 2 and 4
D) 1 and 3
E) 2 and 3
Answer: C
What is the conjugate acid of NH3?
A) +NH3
B) -NH
C) +NH4
D) -NH2
E) +NH2
Answer: C
What is the conjugate acid of CH3NH2?
A) CH3NH3+
B) CH3NH-
C) NH4+
D) NH2-
Answer: A
What is the conjugate base of CH3NH2?
A) CH3NH3+
B) CH3NH-
C) NH4+
D) NH2-
Answer: B
Give the conjugate acid and the conjugate base for HSO4-:
Answer: conjugate acid: H2SO4
conjugate base: SO42-
Write a completed equation for the acid-base pair shown below.
HCO2H + -NH2→
Answer: HCO2H + -NH2 → HCO2 + NH3
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
Answer: C
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.
Answer: 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.
2-Propanol is shown below. Draw the structure of its conjugate base. (CH3)2CHOH
Which of the following is the strongest acid?
A) CH3OH
B) CH3OH2+
C) H2N-
D) CH3NH2
E) CH3NH3+
Answer: B
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.
Answer: C
Which of the following is the strongest acid?
A) HF
B) H2O
C) : NH3
D) CH4
E) CH3OH
Answer: A
Which of the following is the strongest acid?
A) CH3CH2OH
B) CH3OCH3
C) CH3—NH—CH3
D) CH3—C ≡CH
E) CH3—CH =CH2
Answer: A
Consider the set of compounds, NH3, HF, and H2O. Rank these compounds in order of increasing acidity and discuss your rationale.
Answer: NH3 < H2O < HF
When determining relative acidity, it is often useful to look at the relative basicity of the conjugate bases. The stronger the acid, the weaker (more stable, less reactive) the conjugate base. In this case, one would look at the relative basicity of F-, OH-, and NH2-. The relative strengths of these species can be gauged based on the electronegativity of the charged atom in each base.
Since fluorine is the most electronegative, F- is the most stable, least reactive base in the group. This means that its conjugate acid, HF, is the strongest.
Identify the compound with the highest pKa.
A) CH3NH2
B) CH3OH
C) CH3COOH
D) H2O
E) CH3NH3+
Answer: A
Identify the compound with the highest pKa.
A) CH3CH3
B) HCCH
C) CH2CH2
D) CH3OH
E) CH3NH2
Answer: A
Identify the most acidic carboxylic acid.
A) ICH2COOH
B) BrCH2COOH
C) CH3COOH
D) FCH2COOH
E) ClCH2COOH
Answer: D
Which of the following is the strongest acid?
A) I
B) II
C) III
D) IV
E) V
Answer: E
Explain why : NF3 is a weaker base than : NH3.
Answer: 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.
Would you predict trifluoromethanesulfonic acid, CF3SO3H, to be a stronger or weaker acid than methanesulfonic acid, CH3SO3H? Explain your reasoning.
Answer: 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.