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Characteristics of Water
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Water a unique polar covalent molecule so necessary for life that it is found in all cells and around all cells chemical formula of water = H2O two hydrogen atoms and one oxygen atom
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What do these have in common?
They are polar. They have oppositely charged ends
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This is called polarity.
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This is called polarity.
Water also has oppositely charged ends.
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Polarity an uneven distribution of shared electrons within a molecule causing slight opposite charges on opposite ends of the molecule
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Hydrogen Bonds a WEAK chemical attraction between polar molecules
the attraction between the positively charged hydrogen of water and the negative charge that exists on other polar molecules including water itself due to water’s polarity
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Hydrogen Bonds
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How are hydrogen bonds different than ionic and covalent bonds?
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How are hydrogen bonds different than ionic and covalent bonds?
Ionic and covalent bonds hold together substances and are STRONG (shown with solid lines) Hydrogen bonds are attractions between separate molecules and are WEAK (shown with dotted lines)
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Universal Solvent water is able to dissolve many compounds – “like dissolves like” water is able to dissolve compounds with charges water is able to dissolve ionic compounds and other polar compounds, but not nonpolar compounds
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Why is it important that water can dissolve many substances?
wherever water goes (either through the ground or through our bodies), it carries valuable chemicals, minerals, and nutrients
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Universal Solvent Solution Solute Solvent
mixture of two or more substances in which the solute molecules are evenly distributed in the solvent Ex: salt water, sugar water, antifreeze Solute substance that is dissolved Ex: salt, sugar, food coloring Solvent substance that does the dissolving Ex: water, acetone
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Water & Ionic Substances
Why is water able to dissolve salt?
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Water & Ionic Substances
Salt is ionic (made of charged particles) and water is polar (has charged ends).
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Water & Ionic Substances
Click here Salts and Solubility Click “Download” Then click “Open” or “Run” Shake the salt shaker to add pieces of salt to the water. Continue to shake and add salt until you see salt build up on the bottom of the container.
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Water & Ionic Substances
Why are the ions moving in the water? The invisible water molecules are constantly moving. How could we get the molecules of water moving faster to dissolve more salt? Heat up the water.
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Water & Polar Substances
Why is water able to dissolve sugar?
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Water & Polar Substances
Sugar is polar (has charged ends) and water is polar (has charged ends).
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Water & Nonpolar Substances
Why does vegetable oil separate from water when they are mixed in the same container?
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Water & Nonpolar Substances
Why does vegetable oil separate from water when they are mixed in the same container? Vegetable oil is nonpolar (no charged ends), and water is polar (has charged ends).
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Water & Nonpolar Substances
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Cohesion and Adhesion Cohesion Adhesion
attraction between molecules of the same substance Adhesion attraction between molecules of different substances
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Water & Solutions Is this cohesion or adhesion?
Hydrogen Bonding in Water Figure 5, page 31 Holt Biology Is this cohesion or adhesion?
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Surface Tension property of the surface of a liquid to resist an external force the surface can stretch and will not break easily
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Surface Tension
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Surface Tension property of the surface of a liquid to resist an external force the surface can stretch and will not break easily caused by cohesion
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Water & Solutions Surface Tension
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Capillary Action process in which water molecules move up through a narrow tube the attraction of water to the walls of the tube and to the other water molecules around it pulls the water up more strongly than gravity pulls it down caused by adhesion and cohesion
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Water & Solutions Capillary Action
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Water & Solutions Capillary Action
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Water & Solutions Capillary Action
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Capillary Action
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Density of Water (H2O) liquid water has a density of 1 g/mL
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Density Anomaly water is rare in that its solid form (ice) is less dense than its liquid form water
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Density Anomaly
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Density Anomaly water is rare in that its solid form (ice) is less dense than its liquid form water ice floats in water
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Specific Heat the amount of heat required to raise 1 gram of a substance 1 degree Celsius
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WHY?!?!
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High Specific Heat water has a high specific heat (heat capacity)
it takes a lot of energy to heat up or cool down water
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Neutral pH Pure water will ionize (split into ions) to create hydrogen and hydroxide ions. H2O H+ + OH- water hydrogen ion hydroxide
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Neutral pH because of this, water has a neutral pH
pH – a system to measure the concentration of H+ ions in a solution acids and bases can damage living tissues
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Water & Solutions
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This may make you uncomfortable!!!
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Damage to Life Acid HF Hydrofluoric acid Base NaOH Sodium hydroxide
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More on pH later…
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