Question 1

Which of the following statements best explains why the first dissociation constant ($$K_{a1}) of a $$polyprotic acid is much larger than its second dissociation constant ($$K_{a2}$$)?

Accepted Answer

The first proton is removed from a neutral molecule, while the second is removed from an anion, which holds the proton more tightly.

Question 2

A 0.20 M solution of ascorbic acid ($$H_2C_6H_6O_6) $$has $$K_{a1} = 8.5 	imes 10$$^{-5}$$ and K$$_{a2} = 1.6 	imes $$10^{-12}. $$What is the pH of the solution? (Assume only the first dissociation contributes significantly to $$[H^+].)$$

Accepted Answer

$$2.39$$

Question 3

Which of the following acids is expected to have the highest $$K_a$$ value based on its structure and the electronegativity of its central atom?

Accepted Answer

HOClO$$_3$$

Question 4

Given the following binary acids: $$HF$$, $$HCl$$, $$HBr$$, and $$HI$$, which trend is observed as you move down Group 7A in the periodic table?

Accepted Answer

Acid strength increases as bond strength decreases.

Question 5

A 2.2507 g sample of oxalic acid ($$H_2C_2O_4$$, molar mass = 90.03 g/mol) is dissolved in water to make 250.0 mL of solution. $$K_{a1} = 6.5 	imes 10$$^{-2}$$, K$$_{a2} = 6.1 	imes $$10^{-5}. $$What is the pH of the solution? (Use the quadratic formula for the first dissociation.)

Accepted Answer

$$1.27$$

Question 6

Which of the following best describes a polyprotic acid?

Accepted Answer

An acid capable of donating two or more protons in a stepwise manner.

Question 7

For the oxyacids $$HOCl$$, $$HOBr$$, and $$HOI$$, which factor primarily determines their relative acid strengths?

Accepted Answer

The electronegativity of the central atom.

Question 8

Which of the following statements about the acid strength of carboxylic acids is correct?

Accepted Answer

The presence of electronegative atoms in the R group increases acid strength by stabilizing the conjugate base.

Question 9

Which of the following is the correct expression for the second dissociation constant ($$K_{a2}) of $$phosphoric acid ($$H_3PO_4$$)?

Accepted Answer

$$K_{a2} = \frac{[H_3O^+][$$HPO_4$$^{2-}]}{[H_2PO_4^-]}$$

Question 10

Which of the following best explains why $$HCl is a $$stronger acid than $$HF in $$aqueous solution?

Accepted Answer

The H-Cl bond is weaker than the H-F bond, making it easier to ionize.

Question 11

Which of the following is the correct order of acid strength for the following oxyacids: $$HOCl$$, $$HOClO$$, $$HOClO_2$$, $$HOClO_3$$?

Accepted Answer

$$HOClO_3$$ \u003e $$HOClO_2$$ \u003e HOClO \u003e HOCl$$

Question 12

A solution contains 0.10 M oxalic acid ($$H_2C_2O_4) $$with $$K_{a1} = 6.5 	imes 10$$^{-2}$$ and K$$_{a2} = 6.1 	imes $$10^{-5}. $$What is the concentration of $$C_2O_4$$^{2-}$$ at equilibrium?

Accepted Answer

$$6.1 	imes 10$$^{-5}$$ M

Question 13

Which of the following is a correct statement about the calculation of pH for a polyprotic acid when $$K_{a1} \gg K_{a2}$$?

Accepted Answer

The pH can be calculated by considering only the first dissociation.

Question 14

Which of the following would increase the acid strength of a carboxylic acid?

Accepted Answer

Replacing a hydrogen atom in the R group with a chlorine atom.

Question 15

Which of the following is the correct formula for the percent ionization of a weak acid?

Accepted Answer

$$	ext{Percent ionization} = \frac{[H_3O^+]_{eq}}{[HA]_i} 	imes 100$$

Question 16

Which of the following best describes the effect of increasing the number of oxygen atoms in an oxyacid?

Accepted Answer

It increases the acid strength by making the H-O bond more polar and easier to ionize.

Acids and Bases: Polyfunctional Acids, Acid Strength, and Chemical Structure

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