Solutions for Gravimetric Analysis Questions
Check for Understanding 4.1
1.
Determine the solubility of AgCl using Ksp for AgCl and a table of initial and
equilibrium concentration terms.
AgCl(s)
X Ag+(aq) + Cl-(aq)
init
equil
0.0060
0
0.0060 + x
x
where x = increase in [Cl-]
= solubility of AgCl
at equil, Ksp = 1.8 x 10-10 = [Ag+][Cl-] = (0.0060 + x)(x) • 0.0060x
Y x = 3.00 x 10-8 M
2.
Check for Understanding 4.2
1.
Often the solubility of a slightly soluble salt is increased in acidic solution
because the anion combines with H+ to form a weak acid. Removal of the anion
shifts the equilibrium toward more dissolution of the salt. Since Cl- would form a
strong acid (HCl) that is ~100% ionized in solution, it is not removed from
solution. Therefore, AgCl is not more soluble in acidic solution and the presence
of HNO3 does not increase its solubility.
Check for Understanding 4.3
1.
First, determine the solubility of AgCl using Ksp for AgCl and a table of initial and
equilibrium concentration terms.
AgCl(s)
X Ag+(aq) + Cl-(aq)
init
0
0
equil
x
x Solutions for Gravimetric Analysis Questions
at equil,
Ksp = 1.8 x 10-10 = [Ag+][Cl-] = (x)(x)
Y x = 1.34 x 10-5 M
In order to estimate the error that this precipitate mass loss involves, one must
know the total mass of the AgCl precipitate. This can be calculated from the
original unknown sample mass and the mass percent chloride in the unknown.
Assuming a sample size of 0.25 g that is 50% Cl- by mass,
Solutions for Gravimetric Analysis Questions
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