Water and the Chemistry of Life

Water Facts There is the same amount of water on Earth today as there was 3 billion years ago. Three percent of the water on Earth is freshwater and only 1 % is avaiIable for human consumption. Sixty-six percent of a human being is water. Seventy-five percent of the human brain is water. Seventy-five percent of a living tree is water. You could survive about a month without food, but only 5 to 7 days without water.

The Water Molecule The water molecule contains one oxygen atom and two hydrogen atoms.

Properties of Water

Water is Polar Water is polar because oxygen is a “bully” and does not share the electrons.

Water is Polar Oxygen is negative with more electrons and Hydrogen is positive with less electrons.

Water forms Hydrogen Bonds Water molecules attract each other because of Oxygen’s (-) charge and Hydrogen’s (+) charge. Hydrogen bonds hold water molecules together. How many water molecules are shown?

Hydrogen Bonds and the Titanic Hydrogen bonds sank the Titanic. The reason ice floats is because of hydrogen bonding. In other words, ice is less dense than liquid water and will float on the surface of the liquid. Throw in one really big chunk of ice and a cruise ship, and you begin to see the problems that can arise.

Cohesion Cohesion is the attraction of the same type of molecules to each other. Water molecules stick together and “hold hands” with hydrogen bonds

Cohesion Cohesion explains “wetness”. Water molecules stick together and form drops. Cohesion explains why insects can walk on a lake’s surface.

Adhesion Adhesion is the attraction of molecules between two different substances. Example: The attraction of water molecules to a glass.

Adhesion Adhesion causes “this”. ( Name the line and the equipment.) Adhesion causes water to rise in a straw

Adhesion or Cohesion?? Water rising in plants from roots to leaves. Animals walking on surface water tension. Colored celery leaves.

Water is the Universal Solvent Water is polar and can dissolve both salts, sugars, and other molecules.

Water Molecules Can Split A water molecule can split and form ions. H 2 0 H + + OH - An ion is a charged atom. (+ or -)

Water and Acids Acids form H + ions in a water solution. Acid solutions have high concentrations of H + ions and have a pH value less than 7.

Water and Bases Bases form OH - ions in a water solution. Basic solutions have high concentrations of OH - ions and have a pH value greater than 7.

The Water Cycle

Earth's water is always in movement, and the water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth. Since the water cycle is truly a "cycle," there is no beginning or end. Water can change states among liquid, vapor, and ice at various places in the water cycle, with these processes happening in the blink of an eye and over millions of years

The Water Cycle Although the balance of water on Earth remains fairly constant over time, individual water molecules can come and go in a hurry. The water in the apple you ate yesterday may have fallen as rain half- way around the world last year or could have been used 100 million years ago by Mama Dinosaur to give her baby a bath