Chem 1721/1821
Name _________________________________
Quiz 7 (25 points)
April 10, 2014
pX = −log X
pKw = pH + pOH
!=
1.
Kw = 1 x 10—14 at 25ºC
pKw = pKa + pKb
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Benzoic acid is a weak acid (HC7H5O2, Ka = 6.3 x 10–5). 50.0 mL of 0.650 M HC7H5O2 is titrated with 0.882 M RbOH.
a.
Determine the volume (in mL) of RbOH (aq) that must be added to reach the stoichiometric point.
volume = ________________ mL
b.
Determine the pH of the solution after the addition of 12.0 mL RbOH (aq).
pH = ________________
c.
Determine the pH of the solution after the addition of 47.0 mL RbOH (aq).
pH = ________________
2.
3.
a.
Write the balanced net ionic equation for the equilibrium that controls the pH of the solution at the stoichiometric
point in the titration of HF (aq) with NaOH (aq). Include all charges on ions.
b.
Write the balanced net ionic equation that shows the neutralization reaction that occurs when a saturated solution of
strontium sulfate is acidified by the addition of HCl (aq). Include all charges on ions.
c.
Write the equation that describes the solubility equilibrium of iron (II) hydroxide. Include all charges on ions.
Strontium oxalate (SrC2O4) is a slightly soluble salt. What is the mathematical relationship between Ksp and molar
solubility (x) for this salt? Circle the one best answer below.
Ksp = 2x2
4.
Ksp = 108x5
Ksp = 3x
Ksp = x2
Ksp = 27x4
Ksp = 4x3
Different volumes of solutions of Pb(NO3)2 and KI (aq) are combined. After the solutions are mixed, the resulting ion
concentrations are determined. Circle the letter of the one scenario detailed below {A, B, or C} that will result in no
precipitation of PbI2 (s). The concentrations given are of the ions after the sol'ns are combined; for PbI2, Ksp = 6.5 x10–9.
A: [Pb2+] = 4.0 x 10–3 M
[I–] = 4.0 x 10–3 M
B:
[Pb2+] = 5.0 x 10–5 M
[I–] = 0.0025 M
C: [Pb2+] = 0.0048 M
[I–] = 0.0066 M
5.
a.
Consider thallium (I) chloride, TlCl (Ksp = 1.7 x 10–4). In which solution will TlCl be the least soluble?
Circle the one best answer below.
pure water
b.
0.25 M NaCl (aq)
0.25 M BaCl2 (aq)
Silver ions in solution can react with cyanide ion to form the complex ion [Ag(CN)2]– (aq) as shown below:
Ag+ (aq) + 2 CN– (aq)  [Ag(CN)2]– (aq); Kf = 5.6 x 1018.
In which solution will the solubility of AgI (s) be the greatest? Circle the one best answer below.
pure water
6.
0.25 M HCl (aq)
0.25 M HI (aq)
0.50 M KCN (aq)
0.50 M AgNO3 (aq)
A saturated solution of magnesium arsenate is prepared by putting solid Mg3(AsO4)2 in water and allowing the solution
to reach equilibrium. Once equilibrium is reached, the solution is found to have [Mg2+] = 1.4 x 10–4 M . Determine
[AsO43–] in this solution, and Ksp for magnesium arsenate.
[AsO43–] = ____________________ M
Ksp = ____________________
7.
For NiCO3, Ksp = 6.6 x 10–9. Nickel (II) ions in solution can react with ammonia to form the complex ion
[Ni(NH3)6]2+ (aq) given by the equation: Ni2+ (aq) + 6 NH3 (aq)  [Ni(NH3)6]2+ (aq); Kf = 5.6 x 108.
Determine the value of KC for the following reaction: NiCO3 (s) + 6 NH3 (aq)  [Ni(NH3)6]2+ (aq) + CO32– (aq).
KC = ____________________
8.
Consider the titration curve shown below. In this titration, 25.0 mL of a weak base, B, is titrated with 0.365 M HBr (aq).
a.
From the curve, determine the pH at the stoichiometric
point of this titration.
pH = _____________
b.
From the curve, determine the volume of acid that must be
added to reach the stoichiometric point.
vol = _____________ mL
c.
Determine the molar concentration of the base, B, used in
this titration.
[B] = ______________ M
d.
Determine the value of Kb for the base.
Kb = _______________