Chapter 2 Acids and Bases - Quiz 1 PDF

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1/10 Chapter 2 Acids and Bases - Homework Assignment 1 1. Rank the following compounds in order of increasing acidity using the periodic table. Place the least acidic compound at the top of the list and the most acidic compound at the bottom of the list. H 2O

HBr

HF

1 H2O 2 HF F is more electronegative than O and HF is therefore a stronger acid than H2O. 3 HBr HBr is more acidic than HF because Br is larger than F and can more readily stabilize a negative charge. 2. A general Bronsted-Lowry acid is often represented by _____, whereas a general Bronsted-Lowry base is represented by _____. a. B: ; H-A b. H-A ; B: c. H- ; H+ d. H+ ; H-

3. According to the Bronsted-Lowry definition, an acid must contain which of the following?

2/10 a. A carbon-hydrogen bond b. A hydrogen atom c. A lone pair of electrons d. A positive charge 4. A Bronsted-Lowry base must have an “available” electron pair to form a bond to H+. Which of the following structural features allow an electron pair to be used in this way? (Select all that apply.) a. An unpaired electron in the structure b. Atoms with filled octets of electrons c. One or more electron pairs in π bonds d. One or more lone pairs in the structure 5. Which of the following Bronsted-Lowry acid/base classifications are correct? (Select all that apply.) a. CH3COOH is an acid. b. (CH3)3N is a base. c. HCl is a base. d. BF3 is an acid.

6. Which of the following options correctly describe Ka? (Select all that apply.)

3/10 a. [H2O] is not included in the Ka expression for a particular acid. The concentration of water is essentially constant, there it is left out of the Ka expression. b. The magnitude of Ka is inversely related to acid strength. c.

K a=

[ starting materials ] [ products ]

d. Ka is called the acidity constant. 7. Match the appropriate values of Ka and pKa. 

large Ka – small pKa pKa = -log Ka



small Ka – large pKa pKa = -log Ka

8. True or false: A compound with a high pKa value is a strong base. False. A compound with a high pKa value is a weak acid. This means its conjugate base will be a relatively strong base, but it does not necessarily mean anything about the compound’s OWN ability to act as a base. 9. Rank the following compounds in order of increasing acid strength. Place the weakest acid at the top of the list and the strongest acid at the bottom of the list. CH3CH2OH, pKa = 16

Phenol, pKa = 10

CH3CH2CH3, pKa = 50

1 CH3CH2CH3, pKa = 50 2 CH3CH2OH, pKa = 16 3 Phenol, pKa = 10

10. Formic acid has a pKa value of 3.8, while pivalic acid has a pKa value of 5.0. which acid is stronger, and by what degree?

4/10 a. Formic acid is 1.2 times more acidic. b. Formic acid is approximately 10 times more acidic. The pKa scale is a logarithmic scale. A difference of 1 pKa unit translates to a factor of 10 difference in acidity. c. Pivalic acid is approximately 10 times more acidic. d. Pivalic acid is 1.2 times more acidic. 11. When comparing the relative acidity of two acids (H-A) always compare the relative stability of their conjugate bases (B-). The more stable the conjugate base, the more acidic is H-A. 12. Which of the following is the MOST important factor that determines the acidity of an H-A bond? a. The location of element A is the periodic table b. Resonance effects due to element A or groups attached to element A c. The hybridization of element A d. Inductive effects due to groups bonded to element A

13. Which of the following statements correctly explains how the conjugate base of an acid may be resonance stabilized? a. The negative charge is stabilized by delocalization though the π framework.

5/10 b. Increasing the electron density through the π bonds stabilizes the negative charge. c. Resonance allows the negative charge to be concentrated on a single atom, stabilizing it. d. Spreading out the negative charge by electron withdrawal through σ bonds stabilizes it. 14. Which of the following conjugate bases are stabilized by resonance? (Select all that apply.)

a. A b. B c. C 15. Which type of stabilization has a greater effect on the pKa value of an acid: induction or resonance? a. resonance Resonance delocalization usually has a much greater effect on stability than induction. b. Induction

16. Inductive effects refer to the pull of electrons through _____ bonds, while resonance effects operate by delocalization of electrons through _____ bonds. a. π, σ

6/10 b. σ, π 17. Consider a conjugate base of the general formula A-. Rank the conjugate base in order of decreasing stability in terms of the hybrid orbital in which the lone pair of A- is located. Place the most stable situation at the top of the list and the least stable situation at the bottom of the list. sp2

sp

sp3

1 sp The higher the % s-character of the orbital the more stable the conjugate base. 2 sp2 3 sp3

18. An electron pair in an sp hybridized orbital is at a _____ energy than an electron pair in an sp2 hybridized orbital. A conjugate base A- that has its lone pair located in an sp2 hybridized orbital is therefore _____ stable than a base that has its lone pair located in an sp hybridized orbital.

7/10 a. higher, less b. lower, more c. higher, more d. lower, less The greater the s character of the orbital containing the lone pair, the closer the electrons are held to the nucleus, the lower their energy, and the more stable the base. 19. Rank the following compounds based on decreasing acid strength. Place the strongest acid at the top of the list and the weakest acid at the bottom of the list.

1 A A is the strongest acid because the resulting conjugate base will have a lone pair in an sp hybrid orbital. As the % s-character of an orbital increases, the stability of the conjugate base increases, 2C 3 B B is the weakest acid because the resulting conjugate base will have a lone pair in an sp3 hybrid orbital. As the % s-character of an orbital decreases, the stability of the conjugate base decreases. 20. Without using a Ka or pKa table, rank the three compounds shown based on increasing acidity. Place the least acidic molecule at the top of the list.

8/10

1 A Based on periodic trends, hydrogens attached to S are more acidic than hydrogens attached to O. The inductive effect of the Cl atom makes compound B more acidic than compound C. 2C 3 B Based on periodic trends, hydrogens attached to S are more acidic than hydrogens attached to O. The inductive effect of the Cl atom makes compound B more acidic than compound C. 21. The name of the compound shown is p-toluenesulfonic acid, which is often abbreviated as TsOH.

22. Which of the following species are common negatively charged strong bases? Select all that apply. a.

–

NH2

b. –H

9/10 c.

–

OH

d. -Cl 23. Match each substance to its correct description according to each system of defining acids and bases. 

Bronsted-Lowry acid – proton donor



Bronsted-Lowry base – proton acceptor



Lewis acid – electron pair acceptor The Lewis acid-base definition views acid-

base behavior in terms of electrons, not protons. A Lewis acid accepts electrons. 

Lewis base – electron pair donor The Lewis acid-base definition views acid-base

behavior in terms of electrons, not protons. A Lewis base donates electrons. 24. In a Lewis acid-base reaction, the base _____ an electron pair to/from the acid. This is an example of a general reaction trend, i.e., that electron-rich species react with electron_____ species. a. donates, rich b. accepts, deficient c. accepts, rich d. donates, deficient

25. Select the structure of the product formed by the Lewis-acid base reaction between

chloride anion (Cl-) and the carbocation a. CH3CH2CH2Cl

.

10/10 b. CH3CH(Cl)CH3 c. CH3Cl...