Water Notes
-
H20 (2 hydrogen atoms, 1 oxygen atom)
the single most abundant compound in most living things
75% Earth’s Surface is covered in water
Expands as it freezes (Ice is less dense than liquid water)
Characteristics of Water
1. Polarity- oppositely charged regions which attract each
other
- Polar covalent bond between H and O
(Mickey Mouse)
2. Cohesion- an attraction between
molecules of the same substance
- Ex) 2 water molecules joined by a Hydrogen bond
- Surface Tension- causes water molecules to be drawn
inward toward one another causing water to form
beads on smooth surfaces and allowing
insects/spiders to walk on surface of water (and float the pin on the
water)
3. Adhesion- an attraction between molecules of different substances
- Ex) Glass + Water (water in glass dips in middle because water is
clinging to sides
- Ex) Capillary Action – Adhesion causes water to rise in narrow tube
against gravity such as water drawn out of roots of plans up to stems
and leaves
4. Universal Solvent
- Mixture- material composed of 2+ elements/compounds that are mixed
together but not chemically combined
Ex) Salt + Pepper
- Solution- Homogenous mixture where the solute + solvent are evenly
distributed
 Solute- substance that is dissolved. Ex) salt
 Solvent- substance in which the solute dissolved. Ex) water
- Suspension- Mixtures of water and nondissolved matter. Ex) blood
pH Scale
H+ + OH-  H20
pH Scale- indicates the concentration of H+ ions in solution (
- factor of 10
- Ranges from 0 -14
Acid
Neutral
Base
pH
<7
=7
>7
Concentration
More H+ than OHH+ = OHLess H+ than OH-
Examples
Hydrochloric Acid in stomach, pH 1.5
Pure water, pH 7
Bleach, pH 12.5
Buffer- weak acids/bases that react with strong acids/bases to prevent sharp
sudden changes in pH. Keep balance/ HOMEOSTASIS because most biological
processes take place between 6.5 and 7.5
Ex) antacid when upset stomach acts as a buffer
Ex) human blood is a pH 7.2 (buffers keep it between 7-7.4)