Earth Science II (Session 13) Fresh Water Earth Science II (Session 13)

Introduction There are close to 1.5 million km3 of water on Earth. Less then 1% of it is available to the living organisms. Fresh water is constantly replaced by the means of the water cycle.

Water Cycle

Fresh water vs salt water DiSpezio, Michael , et al. (1999)

Available water vs unavailable University of Tannessee at Martin (2002)

Structure of the Water molecule Water the is the only compound that can be found in 3 different material states at normal Earth temperatures. The water molecule: Has 2 hydrogen atoms (H) and one oxygen (O), united by covalent polar bonds. It is not a linear molecule but an angular one, it forms a 104.52° angle between the hydrogen atoms. It is a polar molecule, in other words, it H atoms have a positive charge and its O atoms has a negative charge. DiSpezio, Michael , et al. (1999)

Structure of the water molecule The water polarity makes water a dipolar compound, which can form intermolecular bonds dipolar-dipolar know as hydrogen bridges with other water molecules and any polar compound. DiSpezio, Michael , et al. (1999)

Water Properties Physical properties Data Physical Properties Data Boiling point 100 °C Fusion Point 0 °C Density ( 4 °C ) 1 g/cm³ Ice density ( 0 °C ) 0.92 g/cm³ Specific heat 1 cal/g °C Physical Properties Data Surface tension 72.75 dinas/cm Viscosity ( 20 °C ) 1.01 X 10-3 N-s /m2 Universal Solvent Polar Color Colorless Taste No taste Bloomfield, M. (1997)

Water properties Chemical properties Reacts with metals forming hydroxides or metal oxides and hydrogen gas. Reacts with the metallic oxides forming bases. Reacts with non metallic oxides forming acids. It unites with salts to for hydrates. It takes part in double decomposition reactions of many substances ( Hydrolysis reactions) Bloomfield, M. (1997)

Water is life Water is the most important of all compounds. It is essential for all life forms: plants, animals, microorganism, etc., all these need water in abundance in order to complete their metabolism functions. Approximately 70% of a adult’s weight is water. Fruits and vegetables have even higher percentages; potatoes have 78% of water and apples have approximately 85%.

Importance of water conservation Rains, are the main resource of fresh water on the planet. 75% of rain falls on oceans while only 25% remains on the Earth’s surface. Because of this we need to conserve the water that we have.

Water resources on the surface Rivers Lakes Ponds Dams (Reservoirs) Frozen water

Underground water-bearing resources Water bearing (Wells) Caverns Natural wells Geysers

Class reading Textbook… Science and You: Your water use. Page 323 Science and Society: Protecting groundwater. Page 333

Support material Webpage of the International Year of Fresh Water Webpage of Protection of Underground Water

Bibliography Bloomfield, M. (1997) Chemistry of living organisms. 1st ed. Mexico: LIMUSA. DiSpezio, M. et al. (1999) Science Insights: Exploring Earth and Space. 1st ed. United States of America: Prentice Hall. University of Tannessee at Martin (2002). Structure of the Earth [Data]. University of Tannessee at Martin. Extracted May 5th 2003 from the World Wide Web : http://www.utm.edu/departments/ed/cece/seventh/7I3.shtml