Are all Bronsted-Lowry acids and bases Lewis acids and bases?
Please discuss.

Yes, they are. Bronsted-Lowry acids are proton donors that can be thought
of as electron pair
acceptors because the H^{+} is transferred to the electron pair on
a base. Bronsted-Lowry
bases are proton acceptors. In order to accept a proton, the base must
donate an electron pair to the
proton, so Bronsted-Lowry bases are also Lewis bases. It is important to
note that the converse is not
true--all Lewis acids and bases are not Bronsted-Lowry acids and bases.

Problem :

What is the [H^{+}] of a solution prepared by the dissolution of
26.0 g HF (g) in
1.00 L of water? The K_{a} of HF is 6.6 x 10^{-4}.

Note the use of the equilibrium constant to solve the problem and the
assumption that the amount of
dissociation for weak acids is quite small. That assumption is only
valid
for a weak acid in a solution
where the weak acid concentration is much larger than the value of x. If x is
greater than
5% of the initial
concentration of the acid, then you must solve the quadratic equation
because the assumption
becomes invalid.

Problem :

Given that the K_{b} of NH_{3} is 1.8 x 10^{-
5},
calculate the
K_{a} of the ammonium ion, NH_{4}.

Note the important relationships between K_{w},
K_{a}, and
K_{b}
necessary for solving this problem.