Biology:

“The Chemistry of Life”

The pH Scale

pH SCALE

Every living organism must maintain a certain

pH balance in order to survive.

pH scale indicates how acidic or basic a

substance can be.

pH scale ranges from 0 to 14.

Below 7 is acidic

7 is Neutral

Above 7 is basic

pH SCALE

Acids Compounds that form hydrogen ions (H+)

when dissolved in water.

Acids have a pH below 7

Acids turn blue litmus paper RED

The lower the pH number the more H+ and the

stronger the acid.

Examples: stomach acid, citric acid,

battery acid

Bases Compounds that form hydroxide ions (OH-)

when dissolved in water.

Bases have a pH above 7

Bases turn red litmus paper BLUE

The higher the pH number the more OH- and

the stronger the base.

Examples: soapy water, ammonia, bleach

pH – Human Body

The human body must maintain an internal pH

Most organisms must keep a pH close to 7.0

To prevent illness or death, organisms have a

built-in safety net to resist pH change called

buffers.