Chemistry of Soil & Water PSS 264 Homework

1.  Briefly describe the structural differences between hematite and goethite. Why does climate affect the relative amounts of these two minerals in soils? (5 pts)

2.  Describe how the surface charge characteristics of hydrous oxides and 2:1 layered phyllosilicates differ. (5 pts)

3.  Exactly why would kaolinite make a better sorbent for nonpolar organic molecules than smectite or vermiculite? (5 pts)

4.  Why is it difficult to accurately determine weathering rates in soils? (5 pts)

5.  Describe the general weathering scheme of muscovite to dioctahedral vermiculite. (5 pts)

6.  Calculate the activities coefficients for Al3+ and K+ in a soil solution in which they are each 1 mmolar (10-3 molar) and the balancing anion is SO4-2. Show your work. Why are they so different? (5 pts) 

7.  Phosphorus is not a macronutrient and there should be plenty of total P in most soils. Why is often necessary to add more P to obtain optimum plant growth? (5 pts)

8.  You’ve had a garden for a number of years and have added dairy manure compost to provide nitrogen. Now your soil test is ‘excessive’ in phosphorus. Is this a problem for your garden plants; for your local water body; for your self esteem? What should you do about it? What form of phosphorus is your soil test measuring? (10 pts)