16.4 – 16.5 Student Notes

II. Acid and Base Strengths

A. Background

1. Stronger acids are those that lose

2. Stronger bases are those that hold

B. Relative Strengths of Acids and Bases

1. An acid-base reaction normally goes in the direction

How does this work in terms of equilibrium?

2. In water, the acid strengths of the strong acids appear to be the same; that is, they are “leveled out.”

3. The strongest acids have the __________conjugate bases, and the strongest bases have the _________ conjugate acids.

4. Deciding Whether Reactants or Products are Favored in an Acid-Base Reaction

For the following reaction, decide which species (reactants or products) are favored at the completion of the reaction.

SO₄^2- (aq) + HCN (aq) ¯ HSO₄^- (aq) + CN^- (aq)

C. Molecular Structure and Acid Strength

1. Polarity of the bond to which the H atom is attached

a. The H atom should have a

b. The more polarized in this direction,

2. Strength of the bond

a. How tightly the proton

b. This depends on the size of the atom

The larger the atom, _____________, ________________

In going down a column of elements of the periodic table, the size of atom X increases,

3. Trends in Acid Strength

a. Going across a row of elements of the periodic table, the electronegativity increases,

b. For a series of oxoacids of the same structure, differing only in the atom Y,

c. For a series of oxoacids, (HO)_mYO_n,

d. Acid strength of a polyprotic acid and its anions decreases

4. Concept Check

Which member of each of the following pairs is the stronger acid? a. NH₃, PH₃

b. HI, H₂Te

c. HSO₃^-, H₂SO₃

d. H₃AsO₄, H₃AsO₃

e. HSO₄^-, HSeO₄^-