Properties of Water

Water is ESSENTIAL to life

.

Living organisms are composed mostly of water.

Humans – 65%Jellyfish – 90%Tomato – 90%Elephant – 70%

• H atoms are “attached” to one

side of the O atom• This results in water molecule having a

(+) charge on the side

where the H atoms are and

a (–) charge on the side where oxygen

is.

• This uneven distribution of charge is called polarity.

• Opposite electrical charges attract

• Water molecules tend to attract each other– Side with H atoms (+)

attracts O side (-) of a different water molecule

The +/- attraction between the H (+) of one water molecule and the O (-) of the adjacent water molecule.

Oxygen is slightly negative

Hydrogen is slightly positive

COHESION

• Force that holds molecules of a single substance together is cohesion.

• Cohesion is due to hydrogen bonding between water molecules.

• Contributes to upward movement of water from roots to leaves in plants.

SURFACE TENSION

• Related to cohesion because water molecules are attracted to other water molecules.

• Water molecules at the surface are pulled into body of water which causes it to bead up.

• Because of surface tension, water holds its shape and will not spread out

• For water to spread out, surface tension must be reduced – Chemicals such as

surfactants can reduce the surface tension

• Surface tension enables water-striders to run on water without breaking the surface

ADHESION• Attractive force

between two particles of different substances– Water molecules and

glass molecules

• Capillarity is the attraction between molecules that results in rise of liquid when it is in contact with solid

Temperature Moderation

• Water can absorb or release large amounts of energy in the form of heat with only a slight change in temperature.– known as Heat Capacity

• Another result of the multiple H bonds

• A large amount of heat energy is needed for movement of water molecules to increases the temperature

• Hot summer day – water can absorb large amount of energy from sun and can cool the air without large increase in water temp.

• At night –

gradual cooling water warms the air

• As liquid evaporates, surface of liquid left behind cools down

• Evaporative cooling prevents organisms from overheating – Evaporation of sweat

releases body heat and prevents overheating.

High Heat of High Heat of VaporizationVaporization

Water is Less Dense as Water is Less Dense as a Solida Solid

•Which is ice and which is Which is ice and which is

water?water?

Water is Less Dense as Water is Less Dense as a Solida Solid

• Ice is less dense Ice is less dense as a solid than as a liquid (ice floats)

• Liquid water has hydrogen bonds hydrogen bonds that are constantly being broken and constantly being broken and reformed.reformed.

• Frozen water Frozen water forms a crystal-like latticecrystal-like lattice whereby molecules are set at fixed distances.

Water is Less Dense as a Water is Less Dense as a SolidSolid

WaterWater IceIce

Mixtures

• Composed of two or more elements or compounds that are physically mixed together but not chemically combined

• Water can make 2 types of mixtures: solutions & suspensions

• Suspension: mixtures of water and nondissolved material

• Biological example: blood

SolutionA mixture of…

• Solute– A substance that is put INTO the solvent

to dissolve.

• Solvent– Substance that does dissolves the solute– Water = Universal Solvent

Acids & Bases• An important aspect of a living system is the

degree of acidity or alkalinity• pH scale ranges from 0 – 14• Acids – range from 0 – 6 (0 strongest)

• Neutral is 7• Bases - range from 8 – 14 (14 strongest)

Acids, Bases and Buffers

• H2O H+ + OH_

• Water dissociated into equal amounts of hydrogen ions and hydroxide ions

• The pH of pure water is 7 (neutral)• Acids have more hydrogen ions than hydroxide

ions• Bases have more hydroxide ions than hydrogen

ions