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Biology
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2. Covers ¾ of Earth’s Surface

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2-2 Properties of Water
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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.
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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.
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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.
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The Water Molecule
Hydrogen Bonds
Because of their partial positive and negative charges, polar molecules can attract each other.
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The Water Molecule
Hydrogen bonds form between water molecules.
Hydrogen bonds form between water molecules.
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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.
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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.
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12. Adhesion

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Capillarity
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14. 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.

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

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18. 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

19. 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.

20. 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

21. 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

22. 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

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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.
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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.
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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.
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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
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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
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29. 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.

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

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

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

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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.
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