PHYSICAL PROPERTIES OF SEAWATER

YOU NEED YOUR TEXT BOOKS TODAY

JQ: Jot a list of anything you know about water.

How Unique is Water?

• Water is one of only 3 naturally occurring liquids (mercury and ammonia) on Earth

• Only substance occurring naturally that exists in all 3 states – solid, liquid, and gas – on Earth’s surface

• Extremely large liquid range (0oC - 100oC)

• Expands, becomes less dense as a solid

The Nature of Pure Water

• Water made of 2 hydrogen atoms and 1 oxygen atom

• Water is a polar molecule (+ end & – end)

• Water’s unusual structure causes them to “stick together”

• Water molecules form hydrogen bonds

• Hydrogen bonds not very strong, but make water different from any other substance on Earth

What physical feature of water is ultimately responsible for

giving water its unique physical properties? Explain.

Water is a polar molecule – it has a positive and negative end

Figure 3.1

Hydrogen Bond – attraction between positive end of one water molecule and the negative end of another

Water has…

• Cohesion – sticks to itself

• Adhesion – sticks to others

• Surface Tension – a measure of how difficult it is to stretch or break the surface of water– No waves without

surface tension

Water has…

• Low Viscosity – little resistance to flow

• Good for Earth’s marine organisms – WHY?

The Three States of Water• Water is the only substance that naturally occurs

as a solid, liquid and gas on Earth• Evaporation absorbs heat• Condensation releases heat

Water is Weird

• Density – the mass of a certain volume of a substance

• Solid water is less dense than liquid water

• Water becomes more dense as it cools– Water is most dense @ 4º C– Becomes less dense as it nears 0º C

• Good for the planet – WHY?

Heat Capacity• The amount of heat required to raise the temperature of

1 gram of a substance 1º C– Water has one of the highest– 1 calorie raises 1 gram of water 1º C– It absorbs large amounts of energy before the

temperature changes• Good for earth’s climate – WHY?

Mohave DesertPoint Pleasant

Why is Water Important?

• Water is the universal solvent• Water can dissolve more than any

other natural substance• Water can dissolve many hydrophilic

substances – Ionic compounds– Other polar compounds

• http://programs.northlandcollege.edu/biology/Biology1111/animations/dissolve.html

Figure 3.5

Seawater has dissolved solids…

• Source –– Chemical weathering of crustal rocks– Hydrothermal vents– From volcanic eruptions

Exploring the Density of Water Lab

• Review your notes – What is unique about water’s density as solid/liquid?

• At what temperature is water densest?

JQ: What is a hydrometer? How does it work?

Density…• Pure Water less dense than salt water

• Warmer water less dense than colder water

• Denser near poles or equator?

YOU NEED YOUR OCEANOGRAPHY TEXT BOOK TODAY!

Density…• Density increases as you go deeper

• Ocean is layered, stratified

• Seen in profiles of salinity, temperature, and density

• The greater the difference in density between surface and deep water, the more stable the water column and the harder it is to mix vertically

Figure 3.31

Pressure…• Water is noncompressible – does not

change volume with increasing pressure

• Pressure increases with increasing depth– 1 atm (14.7 lbs/in2) for every 10 m (33 ft)– Pressure in deepest trench ~1100 atm– As pressure increases, gases are

compressed (remember “The Bends”?)

Figure 3.13

Buoyancy• The ability of an object to float by

displacing a volume of water equal to its own weight

Water…• Transmits energy

– Heat– Light– Sound

• Refraction – the bending of light and sound waves due to density differences that affect the speed of energy transmission– The denser the water, the greater the refraction

• Archer fish – evolved to account for refraction in order to hunt

Link

Water is …• Transparent –

transmits light energy readily– Important for

photosynthesis– Oceans are blue

because blue light penetrates the deepest

– Coastal waters sometimes green because blue absorbed

Water…• Transmits sound faster & farther than in air

– 1500 m/s in seawater (& 60 times farther)– 334 m/s in air

• At 1000 m combination of salinity, temp & pressure creates a zone of minimum velocity for sound – the Sofar Layer (sound fixing and ranging layer)– Sound waves produced here do not escape

& travel long distances

Sofar Channel