2.1

Molecules that have at least one hydrogen can be a Bronsted-Lowry acid. Thus HI and H2O are Bronsted-Lowry acids.

Lewis acids are molecules that can accept a lone pair of electrons. Thus, only AlCl3 is a Lewis acid.

2.2

pKa is the negative log of Ka

Ka = 1.3 E-5, pKa = 4.9

Ka = 1.3 E5, pKa = -5.1

Ka = 1.3 E-10, pKa = 9.9

Ka = 2.3 E25, pKa = -25.4

Ka = 7.9 E-12, pKa = 11.1

2.3

CH3COOH is the stronger acid because its pKa is more negative than that of CH3OH. Remember that the more negative pKa suggests a larger Ka values, which implies that the equilibrium constant lies to the right for the dissociation of an acid.

2.4

pKb is the negative log of Kb

Kb = 1.3 E-5, pKb = 4.9

Kb = 1.3 E5, pKb = -5.1

Kb = 1.3 E-10, pKb = 9.9

Kb = 2.3 E25, pKb = -25.4

Kb = 7.9 E-12, pKb = 11.1

2.5

To determine the conjugate base of a molecule, determine the structure after the removal of a proton (H+). Don’t forget to include the formal charge on the conjugate base, typically, it is negatively charged. Note that it is possible to have a double negative. Thus, if the acid has a hydrogen and a negative charge, then the conjugate base will have a double negative.

NH2-; OH-; CH2(-2); CN is not an acid; HS- and S(2-).

2.6

There are more resonance structures of the conjugate base that can be drawn for the first structure. Remember that a stable conjugate base results from a strong conjugate acid.

2.8

HBr should be a stronger acid than HCl, owing to the larger size of the Br atom compared to the Cl atom. If you were to consider electronegativity, then HCl is a stronger acid than HBr.

2.9

F-CH2-CH2-OH is the stronger acid because its conjugate base is stabilized through inductive effect from the more electronegative fluorine atom.

2.10

Since the chlorine of the conjugate base of the second acid is closer to the negative charge, it (the conjugate base) is more stable than the first, where the chlorine atom is much further from the negative charge.

2.1

The conjugate base which has a conjugate acid that has a very positive pKa value is a weak conjugate base. Thus, from the bases shown, the order of base strenghts are:

CH3O- > CN- > F- > Cl-

2.2

a) HCl > CH3COOH > HCN > CH3NO2 > CH3-CH2-OH

b) CN-; CH3CH2O-; Cl-; CH3COO-; CH2NO2-

c) CH3-CH2-O- > CH2NO2- > -CN > CH3COO- > Cl-

2.3

The weakest conjugate base results from the dissociation of a strong acid. Thus, the acid with the more negative pKa value will result in the weakest conjugate base. Thus, the answer is HI.

2.4

F-CH2COOH is the stronger acid. This molecule has the very electronegative fluorine atom in the molecule, which can inductively stabilize the negative charge of the conjugate base.

2.5

Cl3CCOO- This conjugate base has three electronegative chlorine atoms to assist in the stabilization of the negative charge.

b) Cl- The negative charge is on a very electronegative atom, chlorine.

c) Br- The negative charge is on a very large atom, bromine.

2.6

NH3 ----> NH2- + H+

CH3OH -----> CH3O- + H+

H3O+ -------> H2O + H+

HCl -------> Cl- + H+

2.7

HCl; CH3OH; H2; CH3COOH

2.8

Base Acid

Acid Base

2.9

a)

b)

c) There are more resonance structures that can be drawn for the conjugate base of the first moelcule.

2.10