Water

Lecture 13 Water (fig. 1.8)

1. Cells contain 70-95% water

2. Unique properties of water result from Hydrogen bonds

Property	Importance
Very Cohesive	Water transport in plants
High Surface tension	Bugs walk on water
High Specific heat	Blood stays warm
High heat of vaporization	Sweat cools us off
Ice less dense than water	Fish survive winter
Universal solvent	Many molecules dissolve in water

3. Hydrogen bonds and the structure of water.

a. What atoms make up a water molecule?

H₂O

Electrons are pulled slightly towards oxygen atom

causing a partial + and partial - charge.

1) Water dissolves ions and other charged molecules well

"The universal solvent". Water is the medium where chemical reaction happen in organisms

2) Oil molecules are uncharged and do not dissolve in water

3) Like dissolves like

4. pH, acid, base

Exercise: list a few acids, bases and where you have used (or heard of pH) in real life

Encounters with pH:

pool, fish tank, shampoo, heartburn & TUMS, deodorant "SECRET is pH balance for women", perms, soil, ammonia for cleaning,

a. Use red cabbage juice as a pH indicator

b. Human blood is pH 7.4 We die below 7.0 and above 7.8 Why?

c. Water molecules H₂O break apart-->H+ and OH- (about 1/554 million molecules of pure or distilled water). Charged particles are called ions

Acids increase H⁺

Bases decrease H⁺

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Acids Neutral Bases

pH Substance Acid or Base?

2 lemon juice acid

4 tomatoes

7 distilled water

9 baking soda

11 ammonia

Which number represents more H⁺ pH 5 or pH 10?

Besides affecting cellular function, pH also affects nutrient uptake from soils.

Acid soils (pH <5) leads to excess aluminum uptake and aluminum toxicity.
Basic soils (pH > 8) reduces the availability of Fe (iron) and other nutrients. Therefore, most plants will grow better in a slightly acid soil, pH=6. The soils in Phoenix tend to be basic so it is common to add soil sulfur + water to produce sulfuric acid and increase soil acidity.