Acid Base - Basic 10

Question 1

What does pKa represent?
a) The concentration of protons in solution
b) The strength of a base
c) The pH at which an acid is half dissociated
d) The number of hydrogen bonds

Answer 1

Answer: c) The pH at which an acid is half dissociated

Explanation: pKa is the pH at which the concentration of protonated and deprotonated forms of an acid are equal.

Question 2

Which of the following indicates a strong acid?
a) High pKa
b) Low pKa
c) High Ka
d) Both b and c

Answer 2

Answer: d) Both b and c

Explanation: Strong acids have a high Ka (more dissociation) and a low pKa (stronger proton donation).

Question 3

How are Ka and pKa related?
a) pKa = –log(Ka)
b) pKa = 1/Ka
c) pKa = Ka × pH
d) pKa and Ka are unrelated

Answer 3

Answer: a) pKa = –log(Ka)

Explanation: pKa is the negative logarithm of the acid dissociation constant, Ka, which is a measure of acid strength.

Question 4

At pH = pKa, what is the percent ionization of a weak acid?
a) 0%
b) 25%
c) 50%
d) 100%

Answer 4

Answer: c) 50%

Explanation: When pH = pKa, half of the acid is dissociated, meaning the ionized and unionized forms are at equal concentrations.

Question 5

If pH > pKa, which form of the acid predominates?
a) Protonated (HA)
b) Deprotonated (A^–)
c) Both equally
d) Cannot determine

Answer 5

Answer: b) Deprotonated (A^–)

Explanation: At pH values above the pKa, the environment is more basic, so the acid loses a proton and exists mostly in its deprotonated form.

Question 6

Which of the following groups is typically acidic?
a) –CH₃
b) –OH
c) –NH₂
d) –C=O

Answer 6

Answer: b) –OH

Explanation: Hydroxyl groups (–OH), especially in carboxylic acids, can donate protons, making them acidic.

Question 7

What does a low pKa value tell you about an acid?
a) It is weak
b) It barely dissociates
c) It has a high affinity for protons
d) It is strong and donates protons easily

Answer 7

Answer: d) It is strong and donates protons easily

Explanation: A low pKa means the acid dissociates readily in water, releasing protons and acting as a strong acid.

Question 8

Which formula allows you to calculate percent ionization?
a) % = (A^–/HA) × 100
b) % = [HA]/[A^–] × 100
c) % = [A^–]/([A^–]+[HA]) × 100
d) % = Ka × pH

Answer 8

Answer: c) % = [A^–]/([A^–]+[HA]) × 100

Explanation: This formula calculates percent ionization based on the ratio of deprotonated acid to total acid.

Question 9

What happens to the protonation state of an acid as pH increases?
a) Becomes less protonated
b) Becomes more protonated
c) No change
d) Reaches full protonation

Answer 9

Answer: a) Becomes less protonated

Explanation: As pH increases, the solution becomes more basic, favoring deprotonation of acidic groups.

Question 10

Which statement is true about pKa and ionization?
a) High pKa acids are mostly ionized at low pH
b) pKa tells you the temperature of ionization
c) Ionization is independent of pKa
d) Low pKa acids are more ionized at high pH

Answer 10

Answer: d) Low pKa acids are more ionized at high pH

Explanation: A low pKa acid will be increasingly deprotonated (ionized) as the pH rises above its pKa.