CHEM 120 FINAL EXAM 5
1. Hydronium (H3O+) has a pKa of -1.7, and is the strongest acid that can exist in
water. A carboxylic acid (RCOOH) can be protonated by hydronium.So, the pKa of
RCOOH:
A) must be greater than -1.7
B) cannot be determined
C) must be smaller than -1.7
Answer: A
2. What is the molecular formula of carbonic acid? Is it a strong acid?(Section
2.2)
A) H2CO3. It is a very weak acid.
B) H2CO3. It is a weak acid.
C) HCO3. It is a very weak acid.
D) CO2. It is a moderately strong acid.
Answer: A
3. Hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), and acetic
acid (CH3COOH) are the most commonly used acids. Find their pKavalues in
sections 2.2-2.6 (or online) and determine which of the followingsequences is in the
order of ascending acid strength.
A) CH3COOH < HNO3 < H2SO4 < HCl
B) CH3COOH < HNO3 < HCl < H2SO4
C) CH3COOH < HCl < H2SO4 < HNO3
D) HCl < H2SO4 < HNO3 < CH3COOH
Answer: A
4. If HB1 is a stronger BrØnsted-Lowry acid than HB2 (also a BrØnsted-Lowry
acid), which is more likely to be protonated when the two are mixed?
A) HB1
B) HB2
C) Cannot be determined
,Answer: B
5. Which of the above is the correct expression for equilibrium constant K ofthe
acid-base reaction of acetic acid (CH3OOH) and ammonia (NH3)?
A) a
B) b
C) c
D) d
Answer: B
6. Does the relationship between size of B (or B-) and acidity of HB (Section2.6)
apply to the elements of the same row (e.g., C, N, O, F)?
A) Yes B) No
Answer: B
7. To an aqueous solution of acetic acid (CH3COOH, PKa =4.8), NaOH is added
to change the pH to 6.8.What is the ratio of concentrations of CH3COO-and
CH3COOH in the resulting solution? (Hint: write the Ka expression for
CH3COOH, from which you can calculate the ratio using the ratio of Ka and [H])
A) -2.0 B) 2.0 C) 100 D) 0.01
Answer: C
8. A carbonic acid/bicarbonate (H2CO3/HCO3-1) buffer controls the pH of
blood. The pKa of carbonic acid is 6.1 at physiological temperature and thenormal
pH of human blood is 7.3 to 7.4. In human blood, which of the two isin higher
concentration?
A) H2CO3 B) HCO3-1 C) Cannot be determined
Answer: B
9. Which of the pairs below are conjugate acid and base?
a. H2SO4 and SO42-
b. H2CO3, CO2
c. HCl and Cl2
,d. H3O+ and HO-
e. HBr and Br-
A) a,b,c B) a,b,c,d C) a,b,e D) a,b,c,d,e E) e
Answer: E
10. The Ka of acid HB1 is 10 times as large as the Ka of acid HB2. What is
pKa,HB1 - pKa,HB2?
A) 10 B) 1 C) 0.1 D) -1
Answer: D
11. How many bonds can nitrogen have? Which rule or principle should beused?
A) Five bonds; octet rule.
B) Three bonds; octet rule.
C) Three bonds; the Hund's rule.
D) Five bonds; the Aufbau Principle.
Answer: B
12. When two hydrogen atoms meet, they will attract to each other and form
abond(and a H2 molecule). Why?
A) Because electrons like to stay together.
B) Because electrons like to be paired up.
C) Because there is attraction between the electron in one hydrogen atom andthe
nucleus of another hydrogen atom.
D) Gravitational attraction between two atoms binds two hydrogen atoms (orany
two atoms) together into a molecule.
Answer: C
13. How do you determine the number of electron domains on the central atom?
A) Draw Lewis structure of the compound, then add up the numbers of loneelectron
pair, single bond, double bond, and triple bond.
B) The # of electron domains = the # of valence electrons
C) The # of electron domains = the number of atoms the central atom is bondedto.
D) The # of electron domains = the # of valence electrons divided by 2
Answer: A
, 14. Indicate partial charges on each atom of the following two bonds: C-Br andO-N.
A) Carbon has partial negative charge and bromine has partial positivecharge; both
oxygen and nitrogen have no charge.
1. Hydronium (H3O+) has a pKa of -1.7, and is the strongest acid that can exist in
water. A carboxylic acid (RCOOH) can be protonated by hydronium.So, the pKa of
RCOOH:
A) must be greater than -1.7
B) cannot be determined
C) must be smaller than -1.7
Answer: A
2. What is the molecular formula of carbonic acid? Is it a strong acid?(Section
2.2)
A) H2CO3. It is a very weak acid.
B) H2CO3. It is a weak acid.
C) HCO3. It is a very weak acid.
D) CO2. It is a moderately strong acid.
Answer: A
3. Hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), and acetic
acid (CH3COOH) are the most commonly used acids. Find their pKavalues in
sections 2.2-2.6 (or online) and determine which of the followingsequences is in the
order of ascending acid strength.
A) CH3COOH < HNO3 < H2SO4 < HCl
B) CH3COOH < HNO3 < HCl < H2SO4
C) CH3COOH < HCl < H2SO4 < HNO3
D) HCl < H2SO4 < HNO3 < CH3COOH
Answer: A
4. If HB1 is a stronger BrØnsted-Lowry acid than HB2 (also a BrØnsted-Lowry
acid), which is more likely to be protonated when the two are mixed?
A) HB1
B) HB2
C) Cannot be determined
,Answer: B
5. Which of the above is the correct expression for equilibrium constant K ofthe
acid-base reaction of acetic acid (CH3OOH) and ammonia (NH3)?
A) a
B) b
C) c
D) d
Answer: B
6. Does the relationship between size of B (or B-) and acidity of HB (Section2.6)
apply to the elements of the same row (e.g., C, N, O, F)?
A) Yes B) No
Answer: B
7. To an aqueous solution of acetic acid (CH3COOH, PKa =4.8), NaOH is added
to change the pH to 6.8.What is the ratio of concentrations of CH3COO-and
CH3COOH in the resulting solution? (Hint: write the Ka expression for
CH3COOH, from which you can calculate the ratio using the ratio of Ka and [H])
A) -2.0 B) 2.0 C) 100 D) 0.01
Answer: C
8. A carbonic acid/bicarbonate (H2CO3/HCO3-1) buffer controls the pH of
blood. The pKa of carbonic acid is 6.1 at physiological temperature and thenormal
pH of human blood is 7.3 to 7.4. In human blood, which of the two isin higher
concentration?
A) H2CO3 B) HCO3-1 C) Cannot be determined
Answer: B
9. Which of the pairs below are conjugate acid and base?
a. H2SO4 and SO42-
b. H2CO3, CO2
c. HCl and Cl2
,d. H3O+ and HO-
e. HBr and Br-
A) a,b,c B) a,b,c,d C) a,b,e D) a,b,c,d,e E) e
Answer: E
10. The Ka of acid HB1 is 10 times as large as the Ka of acid HB2. What is
pKa,HB1 - pKa,HB2?
A) 10 B) 1 C) 0.1 D) -1
Answer: D
11. How many bonds can nitrogen have? Which rule or principle should beused?
A) Five bonds; octet rule.
B) Three bonds; octet rule.
C) Three bonds; the Hund's rule.
D) Five bonds; the Aufbau Principle.
Answer: B
12. When two hydrogen atoms meet, they will attract to each other and form
abond(and a H2 molecule). Why?
A) Because electrons like to stay together.
B) Because electrons like to be paired up.
C) Because there is attraction between the electron in one hydrogen atom andthe
nucleus of another hydrogen atom.
D) Gravitational attraction between two atoms binds two hydrogen atoms (orany
two atoms) together into a molecule.
Answer: C
13. How do you determine the number of electron domains on the central atom?
A) Draw Lewis structure of the compound, then add up the numbers of loneelectron
pair, single bond, double bond, and triple bond.
B) The # of electron domains = the # of valence electrons
C) The # of electron domains = the number of atoms the central atom is bondedto.
D) The # of electron domains = the # of valence electrons divided by 2
Answer: A
, 14. Indicate partial charges on each atom of the following two bonds: C-Br andO-N.
A) Carbon has partial negative charge and bromine has partial positivecharge; both
oxygen and nitrogen have no charge.
