Chapter 3: Water and Life

Essential Knowledge

2.a.3 – Organisms must exchange matter with the environment to grow, reproduce, and maintain organization (3.1-3.3).

7 Properties of Water

1) Cohesive 2) Adhesive 3) High surface tension 4) Stabilizes temperatures 5) High heat of vaporization 6) Expands when frozen 7) Versatile solvent

1) Liquid Water Is Cohesive

Water sticks to water. Why?

• Because the polarity of water results in hydrogen bonding.

Contributes to transport of nutrients (plants)

2) Liquid Water is Adhesive

Water sticks to other molecules. Why?

• Hydrogen bonding. Plants:

• Water adheres to cell walls (helps pull water and nutrients through plant)

Water transport in trees uses Cohesion and Adhesion

3) Water Has A High Surface Tension

The surface of water is difficult to stretch or break.

Why? Hydrogen bonding. Greater surf tension than most

liquids

4) Water Stabilizes Temperature

Water can absorb and store a huge amount of heat from the sun.

Result - climate moderation Result - organisms are able to

survive temperature changes.

5) Water Has A High Heat Of Vaporization

Heat of Vaporization: • The quantity of heat a liquid must

absorb for 1g of it to convert to a gaseous state.

Results:• Water cools organisms from excessive

heat buildup.• Why?

Hydrogen bonding

6) Water Expands When It Freezes

The distance between water molecules INCREASES from the liquid to the solid form.

Result:• Aquatic life can live under ice.

Why?• Hydrogen bonding

Solids and Liquids

Water Benzene

Floats Sinks

Solid Liquid Gas

States of Matter

7) Water Is A Versatile Solvent

Water will form a solution with many materials.

Considered the best solvent Why?

• Hydrogen bonding

Solvent

The dissolving agent. The material in the greater quantity. Ex:

• Water• Alcohols• Buffers

Water is the best solvent • Why? Versatile (can dissolve MOST

solutes)

Solute

The substance that is dissolved. The material in the lesser quantity. Ex:

• Salt• Sugar• Kool-aid powder

Hydrophilic Materials

Materials that dissolve in water.• Hydro - water• philic - to like or love

Have ionic or polar regions (polar covalent bonds) on their molecules for H+ bonds.

Hydrophobic

Materials that repel water. Hydro - water phobic - to fear Have non-polar covalent bonds.

• Remember: In npc bonds, e- are shared evenly.

Ex:• Lipids• Cell membrane components

Quick Review

What is cohesion? What is adhesion? Name the main reason that water

possesses the properties that it does. Give an example of each of the

following:• Solute• Solvent

Solution Concentration

Usually based on Molarity. Molarity - the number of moles of

solute per liter of solution. Use mass to calculate # of molecules

Moles

The molecular weight of a substance in grams.

One Avogadro’s number of molecules. • 6.02 X 1023 = 1 mole

One Mole of each

Sulfur

Sugar

Copper Sulfate

Mercury Oxide

Copper

Sodium Chloride

Dissociation of Water Water can sometimes split into two

ions.

In pure water the concentration of

each ion is 10-7 M

Dissociation of Water, Continued

Adding certain solutes disrupts the balance between the two ions.

The two ions are very reactive and can drastically affect a cell.

Acids

Materials that can release H+ (when dissolved in water)

pH = 0-7 (6.9) Example: HCl HCl H+ + Cl-

Bases

Materials that can absorb H+

Often reduce H+ (by producing OH- ) pH = 7.1-14 Example: NaOH, blood (7.4-7.8),

bleach

Neutrals

Materials that are neither acids nor bases.

pH = 7 (ish) • Usually 6.5-7.4

Ex:• Urine

pH Scale

A logarithmic scale for showing H+ concentration

pH = - log [H+]

pH Scale

Example:

For a neutral solution:[H+] is 10-7

or - log 10-7 or - (-7)or 7

pH, cont.

Acids: pH <7 etc. Bases: pH >7 etc. Each pH unit is a 10x change in H+

[H+] + [OH-] = 14 Therefore, if you know the

concentration of one ion, you can easily calculate the other.

Buffers

Materials that have both acid and base properties.

Resist pH shifts. Cells and other biological solutions

often contain buffers

Buffers, cont.

Advantage:• Prevents damage to cell/DNA• pH changes can denature proteins

Ex:• Buffers in blood keep pH around a

slightly basic pH Most are acid-base pairs

Summary

Recognize the chemical structure of water. Relate the structure of water to its properties. Identify and discuss the unique properties of

water. Calculate specific concentrations of solutions

(moles). Recognize pH and the pH scale. Recognize acids, bases, and buffers.