Water

Water

Earth the Water Planet

Earth the Water Planet

Special Properties of Water Universal Solvent Transparency Three Physical Phases Density and Temperature High Specific Heat High Heat of Vaporization Low Compressibility “Stickiness” of Water Molecules Viscosity

Polarity of Water Molecules

Hydrogen Bonding Between Water Molecules

Hydrogen Bonding Between Different Molecules

Universal Solvent

Solution = A liquid in which two or more substances are homogeneously mixed.

Solvent = Fluid portion of a solution into which other substances are dissolved.

Solute = A substance that is dissolved into a solvent to produce a solution.

Universal Solvent

NaCl (sodium chloride)Dissolving Into Water

Universal Solvent

Universal SolventNaCl Dissolving Into Water

Universal SolventNaCl Dissolving Into Water

Protein Dissolving Into Water

Universal Solvent

Solubility of Solids In general, the solubility of solids increases

with increases in temperature.

Solubility of Gases In general, the solubility of gases decrease

with increases in temperature.

Importance to Living Things

Water is the solvent in which most of the chemistry of life takes place.

Transparency

Electromagnetic Radiation

Electromagnetic Radiation

Light Intensity and Depth in the Ocean

Spectral Characteristics of Light with Depth

Aquatic plants are able to live and photosynthesize beneath the surface of the water.

Animals are able to see below the surface of the water.

Changing spectral distribution of light with depth influences physiology and behavior of living things.

Importance to Living Things

Three Phases of Water

liquid gas

solid

Three Phases of Water

liquid gassolid

Ice vs Liquid Water

liquidicehydrogen bonds

Melting and Boiling Temperatures of Water

Colligative Properties Dissolved solids increase the boiling point

and decrease the freezing point.

Water exists in all three phases at temperatures found on Earth.

If water behaved like substances with similar molecular weight, water would exist only as a gas and it’s likely that the Earth’s gravity wouldn’t retain water.

Importance to Living Things

Density and Temperature Above 4°C the density of liquid water

decreases as the temperature increases.

As the temperature is decreased from 4°C to 0°C, the density decreases.

Water exhibits a density maximum of 1.0 grams/milliliter (g/mL) at 4°C.

Ice is less dense than water.

Density Behavior of Water

Specific Gravity

Ice floats on top of liquid water. If ice were more dense than liquid

water, then ice would sink, leading to a freezing-over of many lakes and streams.

Importance to Living Things

Ice Floats!

High Specific Heat

1.0 calories of absorbed heat energy will raise the temperature of 1.0 gram of water by 1.0°C.

Water can buffer the environment and living things against extreme changes in temperature.

Importance to Living Things

High Heat of Vaporization At 25°C, 1.0 gram of water must

absorb 580 calories of heat energy in order to be converted from a liquid to a gas.

Water vapor in the atmosphere moderates the Earth’s climate.

Living things may moderate their body temperatures via evaporation of water from their surfaces (evaporative cooling).

Importance to Living Things

Low Compressibility

Liquid water does not compress significantly into a smaller volume.

Water can provide shape and form to a living thing (hydrostatic skeleton). For some organisms a hydrostatic skeleton may facilitate movement.

Aquatic organisms may swim.

Importance to Living Things

Low Compressibility

“Stickiness” of Water Molecules

Cohesion

Adhesion

Surface Tension

Cohesion The binding together of like

molecules; the binding together of water molecules to each other via hydrogen bonds.

Adhesion The binding together of different

molecules; the binding of water molecules to other substances via hydrogen bonds.

Cohesion + Adhesion

Capillarity

Cohesion and Adhesion in Water Transport in a Plant

Importance to Living Things

Surface Tension

Importance to Living Things

Resistance of a Fluid to Flow

Viscosity

Colloids and Suspensions

The viscosity of water may be a significant force resisting movement in very tiny aquatic organisms.

The viscosity of water retards the rate at which small suspended particles may settle through it.

The viscosity of water may influence transport of fluids throughout an organism.

Importance to Living Things

Decomposition of WaterH2O H+ + OH-

1 in 107 water molecules will decompose this way in a container of pure water ( [H+] = 10-7 M).

Note that the concentration of H+ is equal to the concentration of OH-)

Definition of pH

pH = -log[H+]

pH of pure water = -log[10-7] = 7

Acids

HCl H+ + Cl-

Add excess H+ to the solution such that [H+] > [OH-].

Bases

NaOH Na+ + OH-

Remove H+ from the solution such that [H+] < [OH-].

pH Scale

Neutral 7Acidic <7Basic (alkaline) >7

Type of Solution pH Value

pH Scale

Buffers

Chemicals that minimize changes in the pH of a solution.

Enzymes (enzymes regulate chemical pathways in cells and tissues) and other proteins of living things are pH-sensitive.

The pH of physiological solutions may influence chemical equilibria.

Importance to Living Things

Water