SI WS #4
1. A Bronsted-Lowry acid is a proton (donor).
A Bronsted-Lowry base is a proton (acceptor).
A Lewis acid is an electron-pair (acceptor).
A Lewis base is an electron-pair (donor).
2. Why are the terms proton and H+ used interchangeably?
The name proton is often used as a synonym for H+ because loss of the valence electron
from a neutral hydrogen atom leaves only the hydrogen nucleus – a proton.
3. Define the terms conjugate acid and conjugate base.
Conjugate acid – the species that results from accepting a proton
Conjugate base – the species that remains after a proton has been donated from the acid
4. What does the constant Ka measure?
Ka measures acid strength
Ka = [A-][H+]/[HA]
As Ka increases, acidity (acid strength) increases.
As pKa increases, acidity (acid strength) decreases.
What does this mean in terms of pH? Higher acidity = Lower pH
5. Formic acid has a pKa of 3.75 and picric acid has a pKa of 0.38.
a. What is the Ka of each?
Formic acid – (1.78*10^-4)
Picric acid – (0.417)
b. Which is the stronger acid, formic acid or picric acid?
Picric acid is stronger – lower pKa – lower pH
6. In the following reactions, identify the acid/base and the conjugate acid/base. Then write a Ka
expression for the reaction.
a. H2SO4 + H2O <=> H3O+ + HSO4acid
base
c. acid
c. base
Ka = [H3O+][HSO4-]/[H2SO4]
b. CH3COOH + H2O <=> H3O+ + CH2COOacid
base
c. acid
c. base
+
Ka = [H3O ][CH2COO ]/[CH3COOH]
SI WS #4
7. Acid HA dissociates in water to yield a concentration of H3O+ of 1.0x10-4 M. What is its pH?
pH = 4
(-log[1x10^-4])
8. The pKa of water is 15.74. Acetone,
What is the pKa of acetone?
9.9
or
, is a weaker acid than water.
19.3
9. Label the reactants in the following equation as a Lewis acid or Lewis base. Draw the product
that would be formed in this reaction. The product formed in this reaction is called a(n) adduct.
+
acid
<=>
base
AlCl3-N(CH3)3