The Importance of Water Mrs. Terwilliger Advanced Chem 7

PROPERTIES OF WATER We live on a planet that is dominated by water. More than 70% of the Earth’s surface is covered with it. Water is essential for life. It is the major constituent of almost all life forms. Most animals and plants contain more than 60% by volume. Humans depend on water for life processes such as digestion, absorption, circulation, growth and excretion. Without water, life would not have developed on Earth! There is the same amount of water on Earth as there was when the Earth was formed. 97% of earth’s water is salt water. 2% is located in ice caps and glaciers. Only 1% is available for human consumption.

Water has a very simple atomic structure – two hydrogen atoms bonded to one oxygen atom The hydrogen side of the water molecule has a slight positive charge (+) The oxygen side there is a negative charge (-) Water is known as a polar molecule due to the charges of the oxygen and 2 hydrogen atoms. There is a slight positive charge by the hydrogen atoms and a slight negative charge by the oxygen atom.

Water has several unique physical properties: Displays capillary action Drawing towards a substance High surface tension Neutral pH (7) High specific heat: amount of heat required to raise the temp 10C Water exists as a liquid over the range of temperature: 0 – 1000C Liquid water is a universal solvent (can dissolve substances) Ex.) Digested foods are soluble (must break down to be used) Contains hydrogen bonds (holds together the water molecule) Has cohesive and adhesive properties Cohesion: sticks to itself Adhesion: sticks to other substances

Water Frozen When water freezes, it expands. This causes icebergs to float. Water reaches a maximum density at about 4°C This causes bodies of water to freeze on the top first. The expansion upon freezing comes from the fact that water crystallizes into an open hexagonal form. This hexagonal lattice contains more space than the liquid state.

The hexagonal lattice of frozen ice