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

Given a 0.20 M solution of ascorbic acid ($$H_2C_6H_6O_6) $$with $$K_{a1} = 8.5 	imes 10$$^{-5}$$ and K$$_{a2} = 1.6 	imes $$10^{-12}$$, what is the approximate pH of the solution?

Accepted Answer

$$2.39$$

Question 3

Which of the following acids is the strongest based on bond energy and periodic trends?

Accepted Answer

HI

Question 4

What is the main factor that determines the strength of binary acids as you move down a group in the periodic table?

Accepted Answer

Decreasing bond strength between H and the other element

Question 5

Which of the following statements about oxyacids is correct?

Accepted Answer

The acid strength increases with the number of oxygen atoms attached to the central atom.

Question 6

A 2.2507 g sample of oxalic acid ($$H_2C_2O_4$$, mm = 90.03 g/mol) is dissolved in water to make 250.0 mL of solution. Given $$K_{a1} = 6.5 	imes 10$$^{-2}$$ and K$$_{a2} = 6.1 	imes $$10^{-5}$$, what is the pH of the solution?

Accepted Answer

$$1.27$$

Question 7

Which of the following carboxylic acids is stronger, and why?

Accepted Answer

Chloroacetic acid, because the Cl atom withdraws electron density, increasing acidity.

Question 8

For the acid series $$HOClO_3$$, $$HOClO_2$$, $$HOClO$$, and $$HOCl$$, which has the highest acid dissociation constant ($$K_a$$)?

Accepted Answer

$$HOClO_3$$

Question 9

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 10

If the concentration of $$[H_3O^+] in a $$solution is $$4.1 	imes 10$$^{-3}$$ M, what is the pH?

Accepted Answer

$$2.39$$

Question 11

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

Accepted Answer

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

Question 12

Which of the following factors increases the acid strength of an oxyacid?

Accepted Answer

Increasing the number of oxygen atoms attached to the central atom.

Question 13

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

Accepted Answer

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

Question 14

Which of the following is the correct order of acid strength for the hydrides of Group 7A elements?

Accepted Answer

HF \u003c HCl \u003c HBr \u003c HI

Question 15

What is the concentration of $$[C_2O_4$$^{2-}$$] in a 0.100 M $$oxalic acid solution, given $$K_{a2} = 6.1 	imes 10$$^{-5}$$ and $$[HC_2O_4^-] \approx 0.054$$ M after the first dissociation?

Accepted Answer

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

Question 16

Which of the following best describes the effect of an electronegative substituent (like Cl) on the acid strength of a carboxylic acid?

Accepted Answer

It increases acid strength by stabilizing the conjugate base.

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

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