Question 1

Which of the following statements best explains why the C–O bond in methanol ($$\mathrm{CH_3OH}) is $$considered polar covalent?

Accepted Answer

Oxygen is more electronegative than carbon, causing the bonding electrons to be attracted more strongly to oxygen.

Question 2

Given the following pK$$_a$$ values: acetic acid ($$\mathrm{pK_a = 4.76}) $$and methanol ($$\mathrm{pK_a = 15.56}$$), which compound is the stronger acid and why?

Accepted Answer

Acetic acid, because a lower pK$$_a$$ value indicates a stronger acid.

Question 3

Which of the following molecules will have a net dipole moment?

Accepted Answer

Water ($$\mathrm{H_2O})$$

Question 4

What is the formal charge on the oxygen atom in dimethyl sulfoxide ($$\mathrm{CH_3SOCH_3}) if it $$has 6 valence electrons, 4 nonbonding electrons, and is involved in 2 bonds?

Accepted Answer

$$6 - (4 + 2) = 0$$

Question 5

Which of the following best describes a Lewis acid?

Accepted Answer

A substance that accepts an electron pair.

Question 6

Consider the reaction: $$\mathrm{HA + H_2O \rightarrow A^- + H_3O^+}. If$$ $$\mathrm{HA}$$ has a pK$$_a of 5 $$and $$\mathrm{H_3O^+}$$ has a pK$$_a of -1.7$$, will the reaction proceed to the right or left?

Accepted Answer

To the right, because $$\mathrm{HA} is a $$weaker acid than $$\mathrm{H_3O^+}.$$

Question 7

Which of the following compounds can act as both a Brønsted-Lowry acid and a base?

Accepted Answer

Water ($$\mathrm{H_2O})$$

Question 8

Which of the following is a correct statement about resonance structures?

Accepted Answer

Resonance forms differ only in the placement of $$\pi or $$nonbonding electrons.

Question 9

Which of the following is the strongest base?

Accepted Answer

Ammonia ($$\mathrm{NH_3$}$$), pK$$_a of $$conjugate acid $$\sim 35$$

Question 10

Which of the following best describes the inductive effect in organic molecules?

Accepted Answer

The electron-withdrawing or electron-donating effect transmitted through sigma bonds due to electronegativity differences.

Question 11

A molecule of acetonitrile ($$\mathrm{CH_3CN}) $$has a formal charge of zero on all atoms except nitrogen. If nitrogen has 5 valence electrons, 2 nonbonding electrons, and is involved in 3 bonds, what is its formal charge?

Accepted Answer

$$5 - (2 + 3) = 0$$

Question 12

Which of the following is a Lewis base?

Accepted Answer

Dimethyl ether ($$\mathrm{CH_3OCH_3})$$

Question 13

Which of the following bonds is most likely to be ionic?

Accepted Answer

Na–Cl

Question 14

Which of the following molecules has resonance structures?

Accepted Answer

Acetate ion ($$\mathrm{CH_3CO_2^-})$$

Question 15

Which of the following is true about the relationship between acid strength and conjugate base strength?

Accepted Answer

A strong acid has a weak conjugate base.

Question 16

Which of the following compounds is most likely to act as a Lewis acid in a reaction?

Accepted Answer

Boron trifluoride ($$\mathrm{BF_3$})$$

Question 17

Which of the following best explains why benzene ($$\mathrm{C_6H_6}) is $$more stable than expected for a molecule with alternating double and single bonds?

Accepted Answer

Resonance leads to delocalization of electrons, stabilizing the molecule.

Question 18

Which of the following is the correct curved arrow formalism for the reaction of acetaldehyde ($$\mathrm{CH_3CHO}) $$acting as a Lewis base?

Accepted Answer

A curved arrow from the lone pair on oxygen to the Lewis acid.

Chapter 2: Polar Covalent Bonds; Acids and Bases – Study Notes

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