Wednesday, September 10, 2008

Chapter 3 - Section 3 "Acidic and basic conditions affect living organisms"

1. The Dissociation of Water Molecules



When a hydrogen atom is transferred from one water molecule to another, it leaves its electron and is transferred as a HYDROGEN ION, which is a proton with a charge of 1+. This transfer makes the water molecule that lost its proton the HYDROXIDE ION
(OH ˉ) and the molecule that gains the proton becomes the HYDRONIUM ION (H3O+) This dissociation of water molecules happens such that the amount of hydronium and hydroxide ions is about even in pure water. **But if acids or bases are added to water, this equilibrium shifts.** Water has a pH of 7, which means it's neutral.




a. example problems:
  • In an acidic solution where the [ H+ ] = 10 ˉ5 M, the [OH ˉ] = 10 ˉ 9
  • In a basic solution where the [ H+ ] = 10 ˉ 9 M, the [OH ˉ] = 10 ˉ 5

2. Buffer : a substance that minimizes large sudden changes in pH
  • Buffers are combinations of H+ donors and H+ acceptors that form in solutions of weak acids / bases.
  • They work by accepting H+ ions from solution when they are in excess and by donating H+ ions to the solution when they have been depleted.
- EX: bicarbonate is a buffer

  • ACIDS release and so DONATE [H+] ions whereas BASES ACCEPT [H+] ions.
3. Threats to Water Quality on Earth

The burning of fossil feuls is a major source of sulfur oxides and nitrous oxides. These react with water in the air to form strong acids, which fall to Earth with rain or snow. Acid precipitation refers to rain, snow, or fog with a pH lower (more acidic) that pH 5.2. Acid precipitation can damage life in lakes and streams (and when it lands on land it can adversely affect the soil chemistry).


1 comment:

SMABiology said...

Bravo, excellent to include the quality of water on Earth as this contributes to the fitness of the environment.