pH: Acids and Bases
Biology
• 1. Covalently bonded water molecules ionize; the atoms
dissociate (break apart) into ions.
2. When water ionizes or dissociates, it releases a small
but equal number of H+ and OH
ions; thus, its pH is neutral.
3. Water dissociates into hydrogen and hydroxide ions.
4. Acid molecules dissociate in water, releasing hydrogen
ions (H+) ions
• 5. Bases are molecules that take up hydrogen ions or
release hydroxide ions.
• As logarithmic scale, each lower unit has 10 times the
amount of hydrogen ions as next higher pH unit.
Acids
• Defined as: substance that
releases hydrogen ions in a
solution
• Properties:
–
–
–
–
pH below 7
Stings on skin
Tastes sour
Corrosive
• Common Acids:
–
–
–
–
–
–
HCl- hydrochloric acid
Citric acid
Sulfuric acid
Battery acid
Urine
Lemon juice
Bases
• Defined as: substance that releases
hydroxide (OH-) ions in a solution.
• Properties:
–
–
–
–
pH above 7
Strong bases can burn skin
Tastes bitter
Slippery
• Common Bases:
–
–
–
–
–
–
Oven cleaner
Toothpaste
Human Blood
Pepto Bismol
Windex
Baking Soda
• pH scale measures degrees of acidity and
alkalinity
• 1-14 Scale
• Measures hydrogen ion concentration (H+)
• Neutral is 7, example water
How do we test pH?
• pH Paper: Turns a color when placed in a
substance.
• Phenolphthalein: when a drop is placed in the
substance, the color of the substance will
change. Bases turn purple. Acids remain the
same.
• Litmus Test: Base turns blue / Acid turns red
pH and our environment
• If pH is too high or low in our drinking water, it can
alter homeostatic levels. It can potentially kill wildlife.
• Acidic water in your pipes can get corroded, leaving
contaminants in the water.
• Alter the function of enzymes.
• Controls cell processes such as metabolism. The
closer the pH is to 7.35-7.45, the higher your level of
health and ability to resist diseases.
• Ocean acidification. There has been evidence of
ocean acidification during each mass extinction.
How is pH regulated in our bodies?
• Through buffers-> compounds that can bind to H+
ion when the H+ concentration increases and can
release an H+ ion when the H+ ion decreases.
• Buffer “locks up or stops” the H+ ions in order for
our bodies to maintain homeostasis.
• Example-> normal pH of blood is 7.35-7.45 (slightly
basic), therefore a small change could disrupt cells
and potentially be fatal.
Draw the pH Scale
• A change of one pH unit changes the hydrogen ion
concentration by a factor of 10.
• Example: A solution with a pH of 1 has 10 times
more hydrogen ion concentration than a pH of 2;
100 x’s more hydrogen ion concentration than a pH
of 3, etc.
• pH of 1 has one million times more hydrogen ion
concentration than a pH of 7.
• To simplify, scientists converted the exponents -7,
0, and -14 to 7, 0, and 14