unique properties of water overview

The Water Planet

• 97% of all water on our planet is in the oceans.

• Fresh water represents the remaining 3% (2/3 is snow and ice in glaciers / polar ice caps).

• Liquid and solid water cover roughly 3/4 of Earth's surface area.

• 29% of the earth’s surface is above sea level (71% is below )

• 97% of all water on our planet is in the oceans.

• Fresh water represents the remaining 3% (2/3 is snow and ice in glaciers / polar ice caps).

• Liquid and solid water cover roughly 3/4 of Earth's surface area.

• 29% of the earth’s surface is above sea level (71% is below )

Unique properties of water

• Absorbs or releases more heat than most other substances for every temperature degree of change

• Water is a good solvent and can dissolve more substances than other fluids, even rocks

• Water exists in 3 physical states that can power thunderstorms/hurricanes and help transport the sun's energy, nutrients, and organisms

More than half the world's population live within 60km of a coastline

South Florida, USA

Overview

• Chemical properties of water– H bonds– Ice– Salinity and Sources

• Physical properties of water– Biomechanics– Density– Temperature

Chemical properties of water

A. Hydrogen Bonds

B. Crystalline Structure

C. Surface Tension

D. Tensile Strength

E. Specific Heat F. EvaporationG. Molecular InteractionsH. Movement and Transport

Chemical properties of water

A. Hydrogen Bonds

B. Crystalline Structure

C. Surface Tension

D. Tensile Strength

E. Specific Heat F. EvaporationG. Molecular InteractionsH. Movement and Transport

Hydrogen Bonds

O

H H

d-

d+ d+

Hydrogen Bonds

Hydrogen Bonds

WATER VAPORWATER VAPOR

3 physical states of water:

Crystalline Structure

Crystalline Structure

Ice

Surface tensionWater has high surface tension due to lateral and downward attraction between individual molecules, which stretches the water's surface, creating a thin skin

O

H H

d-

d+ d+

Surface tensionWater has high surface tension due to lateral and downward attraction between individual molecules, which stretches the water's surface, creating a thin skin

Surface tension

• Water striders can walk upon the water's surface.

• Members of the neuston depend upon the surface film of water for transport and food.

• Liquid water on surfaces to which it does not adhere well "beads-up."

• Surface tension of the water allows wind to push against it, generating waves in large water bodies.

• [Detergents reduce the surface tension of water (by as much as 70%) and allows it to spread out on a surface.]

Tensile strength

Water is strong under tension.

The force needed to pull pure water apart can be as much as 3 x 107 Newtons/m2

120 lbs = 530 Newtons

Limpet attachment strength = 1 x 106 Newtons/m2

Specific heat

Water can absorb a great deal of energy which goes to breaking hydrogen bonds but does not lead to measurable temperature increases.

Because of the massive number of hydrogen bonds in water, it requires a lot of energy to see even a small change in water temperature.

Evaporation

A water molecule makes the transition from a liquid phase into a gas phase.

Because the escaping molecule had a higher than average energy level, it leaves the liquid cooler (lower in energy) upon evaporation.

Hydrogen Bonds - Summary

• High heat capacity (1 cal/g/°C);• Heat of vaporization (540 cal/g);• Heat of fusion (-80 cal/g);• Solid less dense than liquid phase;• High surface tension

Molecular interactions

Solutes

Dissociation of Water Molecules

KD = [H+][OH-]/[H2O] = 1.8 x 10-16 M

where KD is the dissociation constant

(equilibrium constant) for the dissociation of a proton from a water molecule (the smaller the KD, the stronger the binding)

pH of solutions

pH - an index of the relative concentration of H+ ions in solution

[H+] = [OH-] = 10-7 M in pure water ([H2O] = 55 M)

pH º -log10[H+]

In pure water, pH = 7

pH of solutions

• The pH scale ranges from 0 to 14• The higher the pH, the lower the [H+]

(alkaline, basic solutions have a high pH)• The lower the pH, the higher the [H+]

(acidic solutions have a lower pH)

pH of solutions

Examples:

Gastric juice = 1.0 Seawater 8.0

Orange juice = 4.3 Urine = 6-8.0

Blood plasma = 7.4 Ammonia = 12.0

pH and the sea

• A difference in pH from 8 to 7.8 can significantly decrease coral growth rates

• Increased CO2 in the atmosphere lowers pH

• Active photosynthesis and nitrogenous waste excretion can increase local pH

Water as a polar solvent and Salinity

Strong Electrolytes (substances that dissociate completely when dissolved in water - ions)

Salts consist of ions:

      NaCl ® Na+ + Cl- salt

                    HCl ® H+ + Cl- strong acid

                      NaOH ® Na+ + OH- strong base

For strong electrolytes, KD » ¥

Water as a polar solvent

Weak Electrolytes (substances that dissociate in water only to a small extent (KD » 10-3 M to 10-

11 M)

H2CO3 H+ + HCO3- KD = 1.7 x 10-4 M

KD » 10-3 M to 10-11 M

Carbon dioxide-carbonate equilibrium

CO2(aq) + H2O(l)            H2CO3(aq) (Carbonic acid)

CaCO3(s) + 2 H+(aq)            Ca2+(aq) + H2CO3(aq)

H2CO3            H+ + HCO3

- KD = 4.2 × 10-7

HCO3-     H+ + CO3

2- KD = 4.8 × 10-11

CO2(g)            CO2(aq) (CO2 from the atmosphere dissolves into seawater)

bicarbonate

carbonate

\ High CO2= low [CO32- ]

Ocean acidification

Water as a polar solvent

Because of its small size and polar nature, water dissolves many materials, more than any other liquid

Oceans of water act as sink for CO2 molecules – leads to acidification

Seawater contains almost every known naturally occurring element

Seawater constituents

Component Concentration Percentage of Salinity

chloride  18.98  55.03 

sodium  10.56  30.59 

sulfate  2.65  7.68 

magnesium  1.27  3.68 

calcium  0.40  1.18 

potassium  0.38  1.11 

bicarbonate  0.14  0 

Seawater constituents

• Average ocean water has a salinity of 35.0

• This means that 1000 g of average seawater contains 965 g of water and 35 g of salts.

Seawater constituents

Dissolvedchemicals

Sediments

Eroded rock particles

Volcanic ash and igneous rocks

on land

Wind, water, andice erosion

River and wind transport and deposition

Sedimentary rock on oceanic crust

Sedimentary rock on land

Biological uptake, or absorption of

particles, or precipitation

Wind, water, andice erosion

Fallout of volcanicash over oceans

Compaction andwater loss Subduction, melting,

and vulcanism

Scraped of and upliftedot subduction zone

Seawater constituents

Movement and Transport

Diffusion – high concentrations low concentration

Air vs. water

Mass transport – particles carried by fluid flow

Diffusion

high concentration low concentration

C = concentrationD = diffusion coefficientx = lengtht = time

Mass Transport

high concentration low concentration

Physical properties of water

•Viscosity•Reynolds number, Boundary Layers, and Mass transport

•Density •Temperature

Water as a fluidFluid (flu·id) French fluide, from Latin fluidus, from fluere to flow; akin to Greek phlyzein to boil over): having particles that easily move and change their relative position without a separation of the mass and that easily yield to pressure; capable of flowing.

What is a fluid?

Viscosity (m): the resistance of a fluid to motion or internal friction

Reynolds number (Re): the ratio of inertial forces to viscous forces in a fluid

Density (r): the mass of a substance per unit volume

ViscosityThe viscosity of liquids can vary drastically and decreases rapidly with an increase in temperature.

m = 1 x 10-3 N s/m2m = 50 N s/m2At 20º C

At 100º Cm = 0.07 N s/m2

Reynolds number

Reynolds number

Re = rUx/m

Reynolds number

Re = rUx/m

Re = 1

Re = 108

Copepod swimmingLow Re

Boundary Layers and Mass Transport

Re = 101

Laminar Turbulent

Boundary Layers

Boundary Layers and Mass Transport

Re = 103

Re = 108

Density

the mass of a substance per unit volume

Temperature

Temperature

Thermoclines