AP Chemistry
Practice for the Acid/Base and Aqueous Equilibrium
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.
3). 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(NO3)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?
Answers:
1). a) 26.7 b) 0.0599
2). a) 0.0106 b) 11.15
3). a) 8.7E-4 b) 5.8E-4
c) 8.76
c) 2.73×10–3 d) no change
c) SrF2;; 2E-6