Ka, Kb, and Kw
Problems
1. Ascorbic acid, HC6H7O6, also known as
vitamin C, is a weak acid. It is an
essential vitamin and an antioxidant, A
solution of ascorbic acid is prepared by
dissolving 2.00g in enough water to
make 100.0ml of solution. The resulting
solution ha a pH of 2.54. What is the Ka
for ascorbic acid?
2. Penicillin (MM=356g/mol) an antibiotic
often used to treat bacteria infections is
a weak acid. Its Ka is 1.7 x 10-3.
Calculate [H+] in solutions prepared by
adding enough water to the following to
make 725ml. a) 0.187mol b) 127 g
3. Phenol, once known as carbolic acid,
HC6H5O, is a weak acid. It was one of
the first antiseptics used by Lister. Its Ka
is 1.1 x 10-10. A solution of phenol is
prepared by dissolving 14.5g of phenol
in enough water to make 892ml of
solution. Calculate the pH and percent
ionization.
4. When aluminum chloride is dissolved in
water, Al(H2O)63+ and Cl-ions are
obtained. The Ka for the Al(H2O)63+
ion is 1.2 x 10-5. What is the pH of a
1.75M solution of AlCl3?
5. Phthalic acid, H2C8H4O4 is a diprotic
acid. It is used to make phenolphthalein
indicator. Ka1 = 0.0012 and Ka2 = 3.9 x
10-6. Calculate the pH of a 2.9 M
solution of phthalic acid. Estimate the
[HC8H4O4-].
6. Find the value of Kb for the conjugate
base of the following organic acids,
a. Picric acid – explosives Ka =
0.16
b. Trichloroacetic acid – warts Ka
= 0.20
7. Codeine (Cod), a powerful and
addictive painkiller is a weak base.
Write a reaction to show its basic nature
in water. Represent the Codeine
molecules as Cod.
a. The Ka for its conjugate acid is
1.2 x 10-8. What is Kb for the
reaction?
b. What is the pH of a 0.0020M
solution of codeine?
8. Consider sodium acrylate, NaC3H3O2.
Ka for acrylic acid (its conjugate acid) is
5.5 x 10-5. Write the balanced net ionic
equations for the reaction that makes
aqueous solutions of sodium acrylate
basic. (Hint: NaC3H3O2 is a salt)
a. Calculate the Kb for the reaction
b. Find the pH of a solution
prepared by dissolving 1.61g of
NaC3H3O2 in enough water to
make 835ml of solution.
9. The pH of a household ammonia
cleaning solution is 11.68, and the
Kb=1.8 x 10-5. How many grams of
ammonia are needed in a 1.25 L solution
to give the same pH.
10. A solution of sodium cyanide (NaCN)
has a pH of 12.10.Th Kb for CN- is 1.7 x
10-5. How many grams of NaCN are in
425ml solutions with the same pH?
11. Consider the following six beakers. All
have 100ml of aqueous 0.1M solutions
of the following compounds:
A) HI
B) HNO2 C) NaOH
D) Ba(OH)2 E) NH4Cl F) C2H5NH2
Answer the following with: less than,
greater than, equal to or more
information is needed.
a. The pH is beaker A _______ the
pH in beaker B
b. The pH is beaker C _____ the
pH in beaker D
c. The % ionization in beaker A
_____ the % ionization in
beaker C.
d. The pH in beaker B _____ the
pH in beaker E
e. The pH in beaker E _____ the
pH in beaker F
f. The pH in beaker C _____ the
pH in beaker F.