Properties of Water

Water is ESSENTIAL to life . Living organisms are composed mostly of water. Humans – 65% Jellyfish – 90% Tomato – 90% Elephant – 70%

Structure of the Water Molecule 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

What creates the HYDROGEN BOND? Oxygen is slightly negative Hydrogen is slightly positive What creates the HYDROGEN BOND? The +/- attraction between the H (+) of one water molecule and the O (-) of the adjacent water molecule.

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.

For water to spread out, surface tension must be reduced 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

High Heat of Vaporization 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.

Water is Less Dense as a Solid Which is ice and which is water? 1

Water is Less Dense as a Solid Ice is less dense as a solid than as a liquid (ice floats) Liquid water has hydrogen bonds that are constantly being broken and reformed. Frozen water forms a crystal-like lattice whereby molecules are set at fixed distances. 1

Water is Less Dense as a Solid Ice 1

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

Solution A mixture of… Solute Solvent 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