This is a practice exam for the midterm. The problems in the actual exam will be selected from, and be almost identical to, those shown here, except that the actual mineral will change (although a carbonate will be replaced with another carbonate), or the pH, or the Pco2, or the temperature. If you can work each of the problems on this practice exam without the book, you can work the actual exam problems just as easily. DO NOT MEMORIZE the answers to this exam - that is a waste of time. Learn the method of solution. The point totals shown here are for illustration - they will be slightly different for the actual exam.
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CHEMICAL HYDROGEOLOGY
Practice Midterm Exam
You have 2 hours to complete this exam. State all assumptions. Circle final answers - no circle?, no credit!!. Mark each page with your name, and each page with the problem # you are working on! Use a fresh scratch sheet with each problem - please do not use the back page of the exam. Turn in all work sheets stapled to your test. If you do not know a constant, you may obtain it from the T.A., but you will loose a point or two. Scan the exam and answer the easy ones first, then return for the tougher ones. Mark the skipped questions clearly so you can find them later. Check to be sure you did not accidentally skip a problem. Good luck. Partial credit will be given for incomplete answers that are even related to the correct approach.
a) Write out the reaction of rutherfordine (UO2CO3) dissolving in water, and calculate the solubility constant in water at 25°C. (20)
b) Is rutherfordine more or less soluble than calcite? (5)
c) If a water in contact with and equilibrated to gypsum is exposed to rutherfordine, what will happen? Be specific, i.e. D[Ca]; D[UO2], D[alk], DpH, Dphases (20)
d) What will happen to these constituents if you add NaCl to this system after it has equilibrated with gypsum and rutherfordine? (10)
pH = 7.5
[Ca2+] = 88 mg/l
[Alk] = 320 mg/l
[Mg2+] = 7.3 mg/l
[Silica] = 24.0 mg/l
[SO4=] = 6.7 mg/l
[Na+] = 19 mg/l
[Cl-] = 13 mg/l
a) Convert all analyses to milliequivalents/liter (millimoles for neutral species). Convert alkalinity to meq bicarbonate. Write down beside the mg/l concentration. (10)
b) What volume of 0.1 N HCl is required to titrate a 50 ml sample to the total alkalinity endpoint. (15)
c) What is the concentration of carbonate (CO3=)? (a real number is needed here, "insignificant" is not an acceptable answer) (15)
d) What is the equilibrium PCO2 of this water (10)
e) What is the value for CTCO3 (i.e., DIC) of this water? (10)
f) Is this water charge balanced? What is the %error? YOU MUST SHOW YOUR CALCULATION!! (10)