Question 1

Which of the following best describes a Brønsted-Lowry acid?

Accepted Answer

A species that donates a proton

Question 2

Given the reaction $$\mathrm{HA} + \mathrm{H_2O} \rightleftharpoons \mathrm{A^-} + \mathrm{H_3O^+}$$, which expression correctly represents the acid dissociation constant $$K_a$$?

Accepted Answer

$$K_a = \dfrac{[\mathrm{A^-}][\mathrm{H_3O^+}]}{[\mathrm{HA}]}$$

Question 3

Why do organic chemists use $$pK_a$$ instead of $$pH to $$describe acid strength?

Accepted Answer

Because $$pK_a is $$independent of concentration, while $$pH$$ depends on solution concentration

Question 4

Which of the following bonds is generally the weakest and most likely to be the acidic proton in a molecule?

Accepted Answer

A bond between hydrogen and a highly electronegative atom

Question 5

Given the following acids: HI ($$pK_a = -10$$), HCl ($$pK_a = -7$$), HF ($$pK_a = 3.2$$), which has the most stable conjugate base?

Accepted Answer

HI

Question 6

Which factor increases acidity as it increases?

Accepted Answer

Electronegativity

Question 7

Which of the following is a stronger acid: H$$_2S or H$_2O$$?

Accepted Answer

H$$_2S$$, because sulfur is larger and stabilizes the conjugate base better

Question 8

How does resonance affect the acidity of a molecule?

Accepted Answer

It stabilizes the conjugate base, increasing acidity

Question 9

Which of the following statements about the inductive effect is correct?

Accepted Answer

It refers to electron-withdrawing effects that are transmitted through sigma bonds down the molecule

Question 10

At a pH of 7, what is the major species of valine (carboxylic acid $$pK_a = 2.2$$, amine $$pK_a = 9.5$$)?

Accepted Answer

Carboxylate is deprotonated, amine is protonated

Question 11

Which of the following is the correct Lewis acid in the reaction: $$\mathrm{Cl_3Al} + \mathrm{H_3C-O-CH_3$} \rightarrow$$ ?

Accepted Answer

$$\mathrm{Cl_3Al}$$

Question 12

Which of the following acids has the highest $$pK_a$$ value?

Accepted Answer

CH$$_3CH$_2CH$_3$$

Question 13

If the pH of a solution is greater than the $$pK_a of an $$acid, what is the predominant form of the acid?

Accepted Answer

The acid is mostly deprotonated

Question 14

Which of the following molecules will have the most acidic proton?

Accepted Answer

A molecule with a hydrogen bonded to a fluorine atom

Question 15

Which of the following statements is true regarding the relationship between acid strength and conjugate base stability?

Accepted Answer

A stronger acid has a more stable conjugate base

Question 16

Which of the following factors does NOT increase the acidity of a compound?

Accepted Answer

Decreasing size of the atom bonded to hydrogen

Question 17

Which of the following is the correct $$pK_a$$ for water?

Accepted Answer

$$15.7$$

Question 18

Which of the following acids is most stabilized by resonance in its conjugate base?

Accepted Answer

Nitric acid ($$\mathrm{$$HNO_3$$})$$

Question 19

Which of the following is the correct $$pK_a$$ for acetic acid ($$\mathrm{CH_3COOH}$$)?

Accepted Answer

$$4.75$$

Question 20

At pH = 10, what is the major species of valine (carboxylic acid $$pK_a = 2.2$$, amine $$pK_a = 9.5$$)?

Accepted Answer

Carboxylate is deprotonated, amine is deprotonated

Acids and Bases in Organic Chemistry: Definitions, Strength, and Applications

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