AP Chemistry
Practice for the Acid/Base and Aqueous Equilibrium
Name: _________________
1.) A sample of 40.0 milliliters of a 0.100 molar HC2H3O2 solution is titrated with a 0.150 molar NaOH
solution. Ka for acetic acid = 1.810–5
(a) What volume of NaOH is used in the titration in order to reach the equivalence point?
(b) What is the molar concentration of C2H3O2– at the equivalence point?
(c) What is the pH of the solution at the equivalence point?
2.)
CH3NH2 + H2O ↔ CH3NH3+ + OH–
Methylamine, CH3NH2, is a weak base that reacts according to the equation above. The value of the
ionization constant, Kb, is 5.2510–4. Methylamine forms salts such as methylammonium nitrate,
(CH3NH3+)(NO3–).
(a) Calculate the hydroxide ion concentration, [OH–], of a 0.225–molar aqueous solution of methylamine.
(b) Calculate the pH of a solution made by adding 0.0100 mole of solid methylammonium nitrate to
120.0 milliliters of a 0.225–molar solution of methylamine. Assume no volume change occurs.
(c) How many moles of either NaOH or HCl (state clearly which you choose) should be added to the
solution in (b) to produce a solution that has a pH of 11.00? Assume that no volume change occurs.
(d) A volume of 100. milliliters of distilled water is added to the solution in (c). How is the pH of the
solution affected? Explain.
----- fold here ---- Answers: No looking until you have worked through the problems !!! ----- fold here --1). a) 26.7
2). a) 0.0106
b) 0.0599
c) 8.76
b) 11.15 c) 2.73×10–3
d) no change
APC Ksp
Name: __________________
Below is a recent AP question on Ksp . Avoid “simply” searching for the solutions on the internet as you
need to know how to solve this type of problem on your own.
1. At 25ºC the solubility product constant, Ksp, for strontium sulfate, SrSO4, is 7.6×10-7. The solubility
product constant for strontium fluoride, SrF2, is 7.9x10-10.
(a) What is the molar solubility of SrSO4 in pure water at 25ºC?
(b) What is the molar solubility of SrF2 in pure water at 25ºC?
(c) An aqueous solution of Sr(NO3)2 is added slowly to 1.0 litre of a well-stirred solution containing
0.020 mole F- and 0.10 mole SO42- at 25ºC. (You may assume that the added Sr(NO 3)2 solution does
not materially affect the total volume of the system.)
1. Which salt precipitates first?
2. What is the concentration of strontium ion, Sr2+, in the solution when the first precipitate begins
to form?
(d) As more Sr(NO3)2 is added to the mixture in (c) a second precipitate begins to form. At that stage,
what percent of the anion of the first precipitate remains in solution?
APC Are you ready for an acid/base test?
Name: ____________
TRIS is a weak base (with a pKb equal to 5.7) with the following structure.
Its chemical structural formula is given by (HOCH2)3CNH2
TRIS is used in biochemistry and molecular biology all of the time (especially in
buffers).
1) Where is the basic site on the molecule? The –OH or –NH2 group(s)? Explain.
2) A TRIS buffer is made by adding 12 M HCl to a TRIS solutions until the desired
pH is obtained. Write the chemical reaction showing this reaction.
3) Write the net ionic equation showing how a base reacts with a TRIS buffer.
4) What is the pH of a TRIS buffer prepared by adding 10 ml of 12 M HCl to 1.00 L
of 0.5 M TRIS.