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Why are we spending so much money going to Mars? Gusev Crater on Mars (taken by the Mars Exploration Rover Spirit on Jan. 10, 2004
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Solid Liquid Gas The Amazing Water Molecule Water covers 75% of the Earth’s Surface and makes up 45%-95% of living organisms
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Water is polar. Hydrogen bonds form between water molecules. -- ++ ++ ++ -- H H O Water is both cohesive (sticks to itself) and adhesive (sticks to other types of molecules)
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Figure 3.3 Walking on water
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In ice, water molecules form a crystal lattice. In liquid water, no lattice forms, so liquid water is denser than ice.
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As a result, ice floats.
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Figure 3.5 The structure of ice (Layer 2)
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Ice floats and frozen benzene sinks
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Liquid Gas Molecules have thermal energy n Thermal energy = the kinetic energy of molecular motion Temperature = a measure of how much thermal energy the average molecule of an object possesses Heat = the total amount of thermal energy that an object has: can be transferred from warmer to cooler objects
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Heat vs. Temperature The Pacific Ocean has a low temperature, but a lot of heat
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Ice watersteam Water has high specific heat = the amount of energy required to raise the temperature of 1 gram of substance 1° Celsius
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Areas near large bodies of water have a fairly stable temperature
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Evaporative cooling Water has a high Heat of Vaporization: the amount of heat that must be transferred to a liquid to change it from liquid to gas
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Water as a solvent Since water is polar, the positive and negative ends of a water molecule will be attracted to charged ions or other polar molecules Solvent Solute Solution
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Like dissolves Like Hydrophilic: ionic or polar substances that have an affinity for water Hydrophobic: non-ionic or nonpolar substances that do not have an affinity for water
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Chemical reaction: hydrogen bond shift OR
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Acids, Bases, and the pH scale n Acids = substances that release H+ ions (increasing H + concentration) HCl H + + Cl - n Bases = substances that release OH - ions or accept H + ions (decreasing H + concentration) NaOH Na + + OH - NH 3 + H + NH 4
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Figure 3.9 The pH of some aqueous solutions pH = -log[H + ] Example: Water [H + ] = 10 -7 M So the pH is -log(10 -7 ) = -(-7) = 7
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Buffers are substances that help maintain a constant pH in a solution Example: Carbonic acid
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