chemistry 100

some comments

three questions-- answer only one.

1. IN WHAT CIRCUMSTANCE WOULD HYDROGEN FUELED CARS FILL TO REDUCE CO2 EMISSIONS?

• A car running on Hydrogen would produce only H2O -- would directly contribute no CO2.
• However, we need to look at the source of H2 since none is available as a natural resource.
• Hydrogen produced from nuclear power, hydroelectric projects, solar energy would provide fuel without any CO2 production.
• If the H2 is produced from reactions of C or methane with steam or comes from electricity from a coal or oil fired power plant, we still produce lots of CO2 to move the car. (We just don't produce the CO2 in the car itself)

• In the context of the chapter oxidation is a chemical process that produces or releases electrons and reduction is a process that consumes electrons.
  • oxygen is not required.
  • reactions with oxygen (like the rusting of iron) are examples of oxidation

• The text focuses specifically on the problem of mercury containing batteries-- mercury is toxic.
  • Incineration would spread mercury as vapor
  • Improper disposal can lead to mercury ending up in soil or water also.
• (The remarks below go well beyond what I was looking for, but this seems like a good place to include the discussion.)
• Many papers worried about acids
  • The lead acid (car battery) is the only battery with significant acid content.
  • Anyone exposed directly to this acid could be injured and it could damage plants in the region. Acids mix freely with water and are diluted quickly; they also are often neutralized by limestone in the soil (at least around here.) In the overall picture, this isn't a major concern, since we don't dispose of car batteries that frequently.
  • most flashlight batteries are alkaline cells (contain a base.) The standard NiCad rechargeable battery is also alkaline. Similar concerns exist, but that's not really the major concern.
• Disposable batteries mostly contribute Zn and Mn salts along with an iron shell. These are not particularly toxic materials and pose relatively little problem in landfills.
  • more concern exists if this is good management of resources-- could we use old batteries as sources for Zn and Mn instead of simply as garbage. Would shifting to rechargeable cells be a better use of energy and material resources?
  • one should automatically assume that batteries, once trashed, will corrode and materials will leak out of the case. It may take a few years, but you can't assume that a battery will contain its contents indefinitely.
  • Some trash (old batteries) goes into rivers, fields, etc. and it's hard to prevent that material from reaching drinking water and soil used to grow foods.
• We are typically more concerned with landfills-- carefully controlled areas that collect our trash, put it into a relatively water free hole and cover it up. Eventually what goes into a landfill will end up returning for future generations.
  • in principle, much of our trash may decay (paper, old vegetables, etc.) In practice, modern landfills virtually prevent such normal biological processes.
  • chemistry tells us we won't change elements there-- if you have toxic elements (lead, mercury, cadmium) they will remain there and will remain toxic. All you hope is that they don't get released from the landfill.
• Those three (along with Nickel) are the major concerns now-- they can be very toxic and there is enough used in batteries to be an overall concern. All are associated with rechargeable batteries that have moderately long life, but eventually they fail and will be discarded.
  • Federal and state law now require that lead storage batteries (like those in cars) be kept out of the trash and either handled at hazardous waste sites or shipped to reprocessing plants. (If you can recycle the lead, it stays out of the environment.) Car batteries are big enough and easily recognized and generally don't end up in the trash. Buying a new car battery includes a "disposal tax" to fund such activity.
    • One great disgrace has been the companies that ship US batteries to "reprocessing plants" in Mexico or Latin American countries with lax environmental regulations. These plant often produce terrible local environmental disasters, but they meet our immediate needs and they provide money for fly by night businessmen.
  • Similar regulations apply to rechargeable NiCad batteries, mainly because of concerns over cadmium metal. Most hardware stores will accept batteries for recycle or hazardous disposal.
    • Of course, smaller batteries often slip into the normal trash collection and recycling is well below 50%.
    • You could encourage recycling with a deposit fee, refunded when you return a spent battery. This is not a popular approach, especially if the fee is high enough to make it effective. (Many of the recycling programs around now were created by battery manufacturers and they exist mainly to head off such regulations.)