1. Water

2. Understanding Your Watershed
Nancy Mesner and John Geiger June 2005 (pr)
What is pH?
Understanding Your Watershed pH
pH is a measurement of how acidic or how basic (alkaline) a solution is. When substances dissolve in
water they produce charged molecules called ions. Acidic water contains extra hydrogen ions (H+) and
basic water contains extra hydroxyl (OH-) ions.
pH is measured on a scale of 0 to 14. Water that is neutral has a pH of 7. Acidic water has pH values
less than 7, with 0 being the most acidic. Likewise, basic water has values greater than 7, with 14 being
the most basic. A change of 1 unit on a pH scale represents a 10 fold change in the pH, so that water
with pH of 6 is 10 times more acidic than water with a pH of 7, and water with a pH of 5 is 100 times
more acidic than water with a pH of
What is pH?
pH is a measurement of how acidic or how basic (alkaline) a solution is.
When substances dissolve in water they produce ions. Ions are charged atoms.
A change of 1 unit on a pH scale represents a 10 fold change in the pH.

3. The most common biology formula
H20 H+ + OH –
When the concentration of Hydrogen ions is great it has a LOW pH and is considered acidic.
When the concentration of Hydrogen ions is low it has a High pH and is considered basic.

4. pH Scale

5. Ionic Bonds
When a Sodium (Na) atom forms an IONIC bond with a Chlorine (Cl) atom you get the ionic compound Sodium Choride (NaCl).
NaCl-Sodium Chloride

6. COVALENT BONDS
Here is an example of a covalent compound. Carbon (C) shares it’s electrons with 4 Hydrogen atoms (H) to make the compound methane CH4.

7. Water molecules form a special type of covalent compound called:
POLAR COVALENT BONDS
Thus water is considered POLAR

8. What are polar covalent Bonds?
In POLAR molecules, the electrons shared by the atoms spend a greater amount of time, on the average, closer to the Oxygen nucleus than the Hydrogen nucleus.
These kinds of bonds can lead to the formation of a weak bond called a hydrogen bond.

9. Hydrogen Bonds

10. WHY DOES THIS MAKE WATER SO SPECIAL?
Because water is POLAR it can form hydrogen bonds with other water molecules.

11. What do water molecules look like?
Recent pictures from Richard SayKally’s Lab.
Enhanced computer image