Copyright Pearson Prentice Hall Biology Copyright Pearson Prentice Hall

Covers ¾ of Earth’s Surface

Copyright Pearson Prentice Hall 2-2 Properties of Water Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Water Molecule Why are water molecules polar? A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Water Molecule Polarity An oxygen atom, with 8 protons in its nucleus, has a much stronger attraction for electrons than does the hydrogen atom with a single proton. Therefore, oxygen is an electron hog which slightly pulls the electrons closer to itself. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Water Molecule As a result, the oxygen end of the molecule has a slight negative charge and the hydrogen end has a slight positive charge. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Water Molecule Hydrogen Bonds Because of their partial positive and negative charges, polar molecules can attract each other. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Water Molecule Hydrogen bonds form between water molecules. Hydrogen bonds form between water molecules. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Water Molecule Cohesion is an attraction between molecules of the same substance. Because of hydrogen bonding, water is extremely cohesive. Cohesion explains why some insects and spiders can walk on a pond's surface. Copyright Pearson Prentice Hall

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Copyright Pearson Prentice Hall The Water Molecule Adhesion is an attraction between molecules of different substances. The surface of water in a graduated cylinder dips in the center because adhesion between water molecules and glass molecules is stronger than cohesion between water molecules. Copyright Pearson Prentice Hall

Adhesion

Copyright Pearson Prentice Hall Capillarity Copyright Pearson Prentice Hall

Water expands as it freezes Because of this property, ice is less dense than liquid water. This property can be seen when ice forms and floats on the surface of a pond.

Water exists as all 3 states of matter naturally! Evaporation Condensation Freezing Sublimation Precipitation

Copyright Pearson Prentice Hall http://www.youtube.com/watch?v=DAilC0sjvy0&feature=fvwrel Copyright Pearson Prentice Hall

ACIDS Contain hydrogen ions, H+ also called hydronium ions, H3O+ Taste sour (remember not to taste chemicals as a rule) Dangerous to skin Formed from hydrogen and a non metal

Hydrochloric acid HCl – cleans metals; stomach acid Acids - Examples Hydrochloric acid HCl – cleans metals; stomach acid Nitric acid HNO3 – component of fertilizer Sulfuric acid H2SO4 – car batteries; plastics. This is the single most produced chemical.

Acids - Examples Lactic acid HC3H5O3 – milk, muscle cramps Citric or Ascorbic acid HC6H7O7 – fruit juice, flavored candy Carbonic acid H2CO3 – soda pop Acetic acid HC2H3O2 – vinegar, photographic chemicals

Bases, Alkalines, Antacids Taste bitter Contain hydroxide ions OH- Feel slippery because they dissolve the fats in skin Good grease cleaners Contain a metal and a hydroxide group

Ammonium hydroxide NH4OH – ammonia, found in many cleaners Bases - Examples Ammonium hydroxide NH4OH – ammonia, found in many cleaners Sodium hydroxide NaOH – lye, most common base, found in soap and drain cleaner Magnesium hydroxide Mg(OH)2 – milk of magnesia Calcium hydroxide Ca(OH)2 – lime water, found in cement Sodium bicarbonate NaHCO3 – baking soda, component of antacids

Copyright Pearson Prentice Hall Acids, Bases, and pH Acids, Bases, and pH The pH scale  Chemists devised a measurement system called the pH scale to indicate the concentration of H+ ions in solution. The pH scale ranges from 0 to 14. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Acids, Bases, and pH Strong acids tend to have pH values that range from 1 to 3. Strong bases tend to have pH values that range from 10 to 14. Copyright Pearson Prentice Hall

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Copyright Pearson Prentice Hall Acids, Bases, and pH The pH Scale At a pH of 7, the concentration of H+ ions and OH- ions is equal. Pure water has a pH of 7. Sea water Human blood Pure water Milk Normal rainfall The concentration of H+ ions determines whether solutions are acidic or basic. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Acids, Bases, and pH The pH Scale Solutions with a pH below 7 are called acidic because they have more H+ ions than OH- ions. The lower the pH, the greater the acidity. The concentration of H+ ions determines whether solutions are acidic or basic. Acid rain Tomato juice Lemon juice Stomach acids Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Acids, Bases, and pH The pH Scale Oven cleaner Solutions with a pH above 7 are called basic because they have more OH- ions than H+ ions. The higher the pH, the more basic the solution. Bleach Ammonia solution Soap Copyright Pearson Prentice Hall

Examples of Indicators Litmus Red in an Acid Blue in a Base Phenolphthalein Clear in an Acid Pink in a Base There are many, many others.

Litmus Paper On the left in KOH and on the right in HCl.

Phenolphthalein On the left in an acid and on the right in a base.

Bromthymol Blue On the left in an acid and on the right in a base.

Copyright Pearson Prentice Hall Acids, Bases, and pH Buffers  The pH of the fluids within most cells in the human body must generally be kept between 6.5 and 7.5. Controlling pH is important for maintaining homeostasis. One of the ways that the body controls pH is through dissolved compounds called buffers. Buffers are weak acids or bases that prevent sharp, sudden changes in pH. Copyright Pearson Prentice Hall