Acids, Bases, and pH

1
Acids, Bases, and pH

• A water molecule can react to form ions.
• Water ? ? Hydrogen ion Hydroxide ion

2
The pH scale

• Indicates the concentration of hydrogen ions in
  solution.
• Ranges from 0-14
• 7 neutral or H OH
• Pure water has a pH of 7.
• Each step on scale represents a factor of 10.
  Solution with pH of 4 has 10 times as many H ions
  as a solution with pH of 5.

3
The pH scale

• Acids

• Bases

• Any compound that forms H ions in solution.
• pH will be lower than 7
• Hydrochloric acid produced by the stomach to
  digest food is a strong acid with pH around 1.5

• Any compound that forms OH- ions in solution.
• pH will be higher than 7
• Bleach has a pH of 12.5

4
Buffers

• Are weak acids or bases that can react with
  strong acids or bases to prevent sharp, sudden
  changes in pH.
• Our body needs buffers to control pH in order to
  maintain homeostasis. Our body cells generally
  like to be kept in a pH between 6.5 and 7.5.

5
Check

• Rainwater (pH 5.5), Tomato Juice (pH 4.0),
  Gastric juice (pH 2.0). Which has the highest
  concentration of OH- ?
• When pH in the stomach increases from 3 to 5, how
  does the hydrogen ion concentration change?