MINEQL Questionnaire

Turn in all appropriate MINEQL input, assumptions and output. Make surethat each question is answered and that the final answer(s) is highlighted
on the MINEQL output.
Section 1: Acid/base/alkalinity
1. Use MINEQL to:
a) Generate a log C vs pH diagram for a 10-3 M phosphate (PO4) system
b) Determine the pH of the following solution at
equilibrium: Recipe: [Na2HPO4) = 10-3 M, [HCI] = 10-3
M
Note: Turn in a pc-pH diagram and output showing the pH of solution at
equilibrium
2. Find the pH of the following solution at equilibrium.
10-6
Recipe: [NH4Cl]1 = 10-3 [NaOH] = 10-3, P NH3 =
atm Species: H20, H*, OH, Na+, CI, NH4+, NH3(aq),
NH3(g)
Reactions: NH4* = NH3(aq) + H+ pka = 9.2
NH3(g) = NH3(aq) PKH = -1.8
3. Calculate the alkalinity of a carbonate solution in equilibrium with the
atmosphere (Pco2 = 10-3.5) and a having a pH = 7.3. Assume only
carbonate system is important.
1
Section 2: Precipitation and dissolution problem
a) Generate a solubility diagram (p[Fe] dissolved vs. pH) from pH 0 to 14
for a system in equilibrium with solid goethite (FeOOH (s)) using
MINEQL. Show only dissolved Fe+3 species and Fe+3 total dissolved.
b) In the closed, model freshwater system described below, having Cat =
10-4 M and Ct = 10-2 M, at what pH, if any, will calcite (CaCO3)
precipitate? Ignore all other solids. Show appropriate MINEQL output to
support your answer.
pH = ?
TOTCa = 1 E-4
TOTK = 6.0E-5
TOTSO4 = 1.0E-4
TOT Na = 2.8E-4 M
TOTMg = 1.6E-4
TOTCI = 2.0E-4
TOTCO3= 1 E-2
c) At what [Ca*?] concentration, if any, would calcite precipitate in a
closed freshwater with the following composition? Ignore all other
solids. Show appropriate MINEQL output to support your answer.
Freshwater model:
pH = 8.1
TOTCa = ?
TOTK = 6.0E-5
TOTSO4 = 1.0E-4
TOT Na = 2.8E-4M
TOTMg = 1.6E-4
TOTCI = 2.0E-4
TOTCO3= 1 E-3
2
Section 3: Complexation chemistry problem
4. Using the models specified below, determine the total solubility of Cd(OH)2(s)
expressed as [Cd+2+ (aq)] in seawater and freshwater (total refers to the sum of
all dissolved Cd+2 forms). Ignore all other solids. Which type of water yields the
highest total dissolved concentration of cadmium (Cd+2+ (aq)]? Show appropriate
MINEQL output to support your answer.
Seawater model:
pH = 8.1
TOTCa = 1.02E-2
TOTK = 1.02E-2
TOTSO4 = 2.82E-2
TOTNa = 4.68E-1 M
TOTMg = 5.32E-2
TOTCI = 5.45E-1
TOTCO3= 2.38E-3
Freshwater model:
pH = 8.1
TOTCa = 1 E-4
TOTK = 6.0E-5
TOTSO4 = 1.0E-4
TOTNa = 2.8E-4 M
TOTMg = 1.6E-4
TOTCI = 2.0E-4
TOTCO3= 1 E-3
5. Using the seawater model specified in the previous problem, determine the
inorganic speciation of mercury (II) (i.e. calculate the % distribution of all
dissolved Hg+2 species). Assume no solids and a Hg+2 concentration of 1E-10 M.
6. A freshwater lake with the simple composition
Nat = Cat = Mgt = KT = Clt = [SO4]1 = [CO3]1 = 10-3 M
Contains an organic complexing agent X characterized by
+
HX = H+ + X- log Ka = -7.0
CuX+ = Cu 2+ + X log K = -10.0
CaX+ = Ca2+ + X- log K = -2.0
MgX+ = Mg2+ + X log K = -2.0
Calculate the dissolved copper speciation at pH 9 when Cut = 10-8 M, XT = 10-6
M. Do not consider solid phases or ionic strength effects.
3
Section 4. Redox
7. Assume the equilibrium pe in an aquatic system is controlled by the
concentrations of S042 and HS. Calculate the pe of the system, [Fe2, and
[Fe+ ] if [SO ] = 10 Mand [HS] = 10 M, pH = 8, and [Fer] is 2E-6. Ignore all
solids.
8. Determine which form of total dissolved iron (Fe+2, or Fe+3T) would dominate
if the pH = 8 and pe = 4.0 and Fet = 2E-6. Ignore all solids.
9. Assume a normal earth atmosphere (pO2 = 10-0.7 atm), pH =8, and that the
copper species are in equilibrium with the O2/H20 couple. What are the
predicted equilibrium concentrations of Cu+1 and Cut2 under these conditions for
a solution containing 10-4 M total copper? Ignore all solids.
10. Assume a normal earth atmosphere (pO2 = 10-0.7 atm), pH =8, and that the
aqueous sulfur species (SO42 and HS-) are in equilibrium with the Oz/H20
couple. Calculate the equilibrium concentrations of the three sulfur species under
these conditions for a solution containing 10-6 M total sulfur?
4