Problem Set 5
Due Wed. Nov. 24 (before Thanksgiving break)
Part A. Quantitative Problems (3-4 hr, 25 pts)
1. The table below lists the number of bacteria present in a dish of room-temperature potato salad at different times after the dish was prepared.
|
Time (hours) |
Bacteria count (thousands) |
|
0.0000 |
0.035000 |
|
2.0000 |
0.094000 |
|
4.0000 |
0.24100 |
|
6.0000 |
0.60000 |
|
8.0000 |
1.5000 |
|
10.000 |
4.0000 |
|
12.000 |
11.000 |
|
14.000 |
21.000 |
|
16.000 |
32.000 |
|
18.000 |
35.000 |
|
20.000 |
33.000 |
|
22.000 |
34.000 |
|
24.000 |
32.000 |
a) Plot the bacterial population vs. time. Attach the graph.
b) Why does the curve have this particular shape?
2. Spiro's Figure 4.5 (located on p 258 in the back of your text) shows the global fluxes and pools of nitrogen, both in pre-industrial times and for a recent year (1994).
a) Given the fluxes of nitrogen shown, was there any net accumulation of nitrogen in land or ocean during pre-industrial times?
b) Given the fluxes of nitrogen shown, is there any net accumulation of nitrogen in land or ocean today?
c) The Issues in Ecology reading (Human Alteration of the Global Nitrogen Cycle) also lists global nitrogen fluxes. Compare the estimates for the total amount of anthropogenic fixed nitrogen from this reading with those given in Spiro. Why are the two estimates different?
3. a) What is the difference between a molar mass and a formula weight?
b) A student is trying to balance the equation for the reaction of nitrous oxide (N2O) with molecular oxygen to give nitrogen dioxide (NO2). Her answer is given below:
2NO + O2 -----> 2 NO2
Is this answer correct? Explain why or why not.
c) Why does the atomic weight of helium, 4.00260 a.m.u., exactly equal the weight of one mole of helium atoms, 4.00260 g?
d) Some common nitrogen-containing fertilizers include ammonia and ammonium nitrate. For these two compounds, calculate both their formula weight and the % nitrogen by weight.
4. The Haber process is the main industrial method for "fixing" nitrogen. Molecular nitrogen is reacted with hydrogen gas (H2) to form ammonia. The hydrogen can come from many sources, but the most common source is methane, CH4. The methane is first reacted with water to form carbon monoxide (CO) and hydrogen; this process is called steam reforming. Next, the CO is reacted with water and forms carbon dioxide and more hydrogen; this reaction is called the water-gas shift.
a) What is the overall chemical equation for the generation of hydrogen from natural gas?
b) Assuming the hydrogen for the Haber process came from natural gas (methane), how many moles of methane would be required in order to make 100 kg of ammonium nitrate?
5. Suppose DDT is applied to a field each year to eradicate Fuzzy Burrowing Beetles (FBBs). Assume that one out of a million FBBs possesses an enzyme which allows it to break down the insecticide into harmless products. Assume further that a group of FBBs can double its population in 24 days.
a) For how many years will DDT provide useful pest control of FBBs?
b) Why are pesticides that are persistent and fat-soluble more harmful than ones which are quickly degraded and/or water-soluble?
Part B. (6-8 hr, 50 pts) Dr. Pro and Dr. Anti are back for a return engagement. The issue which they are debating now is population growth, as described below:
Resolved: Attempts to curb global population growth should be discontinued because the resulting increase in global population will not cause scarcity of food or other resources in the foreseeable future (to the year 2100).
You will find ample evidence propounded by the Pro side of this resolution at Simon's web site,which hosts the complete text of Julian Simon's book, The Ultimate Resource 2.
The Anti side is ably represented by Lester Brown in an article in Technology Review and by articles in New Scientist, September 3, 1994, Features, Pg. 24, and U.S. News & World Report, September 12, 1994, WORLD REPORT; Vol. 117, No. 10; Pg. 63 (both of these articles are available in full text version on Lexis/Nexis).
The Anti side (represented by Paul and Anne Erlich) gets in some good shots at Simon in an article in Technology Review
Simon fires back at his critics
Your task is to write the dialog for both sides of the debate. This will require at least 3 pages (typewritten, please) of text + figures, in which
b) Each debater must also rebut the two main arguments presented by his or her opponent.
For this assignment, please do not include arguments relating to the morality of methods used to curb population growth. The focus should be on population growth, food, and/or other resources.