Department of Geosciences
North Dakota State University
GEOLOGY 428/628:
Geochemistry
Homework 3
Geology 428/628
Homework 3 - 2008
1. Consider a beaker of pure H2O that is in equilibrium with CO2 gas at different pressures. What is the pH in equilibrium with CO2 gas at a pressure of
2. Assume we measured the pH of two waters in class. The measured values are:
Distilled, deionized water: ____6.0____; Tap water: ____7.7____
(a) In order to make a better reading of pH we add NaCl to the waters. Why doesn't the addition of NaCl alter the pH reading?
(b) What is the concentration of dissolved salts (in equivalents) in each of the waters? (assuming equilibrium with air and no other dissolved anions)
3. Assume Lauren Sager used a straw to blow bubbles into our distilled, deionized water. The pH we measured in distilled water for exhaled breath is _____5.0____.
What is the p(CO2) of Lauren's breath?
4. Use a spreadsheet such as Excel to calculate the SI of gypsum, amorphous SiO2, and quartz for the Mississippi River water analysis given in Faure, table 10.2. Hand in a printout of your spreadsheet.