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 is pH regulated in our bodies?
• Through buffers-> compounds that can bind to H+
ions 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). Any small change could disrupt cells and
could potentially be fatal.
pH and our environment
• If pH is too high or low in our drinking water, it can
alter homeostatic levels, and 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.
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.
• Red cabbage indicator: contains a water soluble
pigment called anthocyanin that changes color when
it is mixed with an acid or base. The pigment turns
red in acidic environments and bluish-green in
alkaline (basic) environments
(www.stevespanglerscience.com).
Tasks to Complete
• 1. Review questions
• 2. pH scale assignment
• 3. Acid / base color, read, and answer packet.