The Wonders of Water

Why Water? 

1.) Water is an important molecular compound that supports life on Earth.

2.) Properties of Water explain hydrophobicity and boiling point.

                                polar molecule     water molecule     H2O Lewis dot

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Chemistry explains the properties of water. First, water is a polar molecule. The polar molecule has two partial positive Hydrogen molecules and one partial negative Oxygen molecule, creating a dipole moment cause by the differences in electronegativity among the molecules. Due to polarity, water molecules are a universal solvent with the ability to dissolve other polar molecules in solution by attracting and separating ions from other substances. Second, water has Hydrogen bonds. Hydrogen bonds are the strongest bonds formed between molecules. Water’s Hydrogen bonding contributes to its polarity. The Hydrogen bonding also allows water to have a solid form less dense than a liquid form, a high boiling point of 100.0 degrees Celsius, and a high heat capacity. Finally, water has amphoteric properties. Meaning, water molecules are able to create both an acid with H+ ions and a base with OH- ions when polar bonds are broken. We can extend these polar properties of water to explain hydrophobicity and boiling point.

Water Repelling Chemistry!

Raincoats, car windshields, and household paints are made to repel water molecules. In order to achieve this, the surface area of a substance must be hydrophobic, ‘afraid of water.’ The hydrophobic effect occurs when non polar substances aggregate in aqueous solution to exclude water; that is, the non polar molecules will repel the polar molecules. Hydrophobic surfaces are made up of polymers, such as, polysiloxanes or polyfluorinated compounds. Many consumer products are designed with theses polymers to create hydrophobic properties. For example, raincoats are designed with Gore-Tex, a compound substance with PTFE, polytetrafluoreothylene, creating a waterproof coating on clothing. In addition, car windshield treatments are coated with Rain-X, a substance containing polysiloxenes compounds to attain hydrophobicity. Finally, some walls are coated with hydrophobic paints to repel water molecules. water repelling chemistry

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What Temperature Does Water Boil At? Boiling Point and Elevation. 

The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid, and then the liquid changes into a vapor. Water, and other substances, change states once the chemical bonds are broken in the compound. Water, at sea level, has a high boiling point because it takes more energy to overcome the strong polar and strong Hydrogen bonds. At sea level, water has a boiling point of 100.0 degrees Celsius. Why does water’s boiling point change? It is true that at higher elevations water’s boiling point decreases. However, water’s boiling point varies not because of elevation, but because of atmospheric pressure and temperature. Atmospheric pressure decreases at higher elevations, and therefore the vapor pressure for water to transform into the gas phase decreases. In addition, vapor pressure will decrease at decreased temperatures as more molecules have the kinetic energy to overcome attraction with other molecules.  Lower pressures allow molecules to escape more easily as the vapor pressure required for a state change decreases. Bonds between molecules, temperature, and vapor pressure explain why water exhibits its lowest boiling point of 69.94 degrees Celsius on Mt. Everest, where the elevation is 8848m, pressure is o.33atm, and temperature is between -20 and -40 degrees Celsius. water boiling point .png

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In conclusion, understanding the chemistry, and more specifically, the polarity of water molecules develops our understanding of hydrophobicity and boiling point of H2O. We can further extend our knowledge of hydrogen bonds to explain properties of the ocean. Did you know that hydrogen bonding among water molecules creates a high heat capacity for water? Water’s high heat capacity allows the ocean to thermoregulate coastal climates. For example, the coastal city, Charleston, South Carolina has an annual high average temperature of 76.1 degrees Fahrenheit and an annual low average temperature of 55.6 degrees Fahrenheit as compared to the upstate city Columbia, South Carolina with an annual high average temperature of  75.3 degrees Fahrenheit and an annual low average temperature of 52.3 degrees Fahrenheit. The ocean will absorb heat emitted, hydrogen bonds are broken, which in turn cools the atmosphere in the summer. Furthermore, the Ocean will release heat, hydrogen bonds are formed, which in turn warms the atmosphere in the winter.

Sources: 

http://cen.acs.org/articles/94/i15/Periodic-graphics-Water-repelling-chemistry.html

What Temperature Does Water Boil At? Boiling Point & Elevation

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