Facts about WATER

  • Water is the most common liquid on Earth.

  • Water covers 3/4 of the Earth’s surface.

  • Makes up 70% - 95% of the weight of living things.

  • Water is an excellent solvent. This means it is good at dissolving solutes.
    The Properties of Water

    1) WATER HAS A HIGH SURFACE TENSION.
    Water is polar (it weakly bonds with other water molecules).
    There appears to be a film on the surface of water.
    This is caused by very weak hydrogen bonds.
    Examples:
    Some insects can walk on surface tension of water.
    Skipping stones across the surface of a pond deflects off of the surface tension.

2) CAPILLARY ACTION
Water creeps up in the thin tubes of plant roots and stems. These water carrying
tubes in a plant are called xylem.


3) ADHESION - Water molecules stick to (adhere to) other substances.
Example: Water sticking to a wall.

4) COHESION - Water molecules sticking to other water molecules.
Example: Water molecules weakly hydrogen bonding to other water molecules are
what creates surface tension (described in Property #1)


5) EVAPORATIVE COOLING
Temperature = a measurement of the movement of molecules.
Hotter = Faster moving molecules
Colder = Slower moving molecules
Examples:
Sweat cools the body.
When water evaporates from a large body of water such as a lake or the ocean, the
hottest (fastest moving) molecules go first. This leaves the molecules remaining
behind with a lower average temperature.


6) HIGH SPECIFIC HEAT
It takes a lot of energy to heat up water. This means that water resists temperature
change. The larger the volume of water, the longer it takes to heat up or cool down.
Calorie - The amount of heat needed to raise 1g of water by 1°C.
Small puddle = freezes quickly/evaporates quickly
Large lake = freezes very slowly/evaporates very slowly
Example: Water helps stabilize/maintain body temperature (Homeostasis)

7) WATER EXPANDS WHEN IT FREEZES
Most things contract or get smaller when they freeze (metals), but water expands
when it freezes. This lets ice float on the surface of water.
Examples:
Water can split rocks when it freezes causing erosion or landslides.
Ponds freeze on top insulating the water (and life) below the surface. This is why
ice fishing is possible.

8) WATER IS A POLAR MOLECULE

Polarity results from the unequal distribution of charge in a molecule.