Acids, Bases

1
Acids, Bases pH
2
What are Acids?

• Acids taste SOUR
• Lemons, vinegar
• Compounds that have Hydrogen (H) as their
  cation.
• Examples
• HCl Hydrochloric Acid
• H2SO4 Sulfuric Acid

3
Acids Form Hydronium Ions

• When acids dissolve in water, their ions
  separate. The Hydrogen ion (H) combines with
  H2O to form a Hydronium ion (H3O)
• Acids are PROTON DONORS (they give their hydrogen
  ion away)

H
Cl

H2
O
?

H3O
Cl-
4
More Info About Acids

• Anything with high concentration of Hydronium ion
  is considered to be an acid.
• Acids turn blue litmus paper RED

5
What are Bases?

• Bases are bitter and slippery.
• Bases either have Hydroxide (OH-) as their anion
  OR they will form Hydroxide in solution
• Examples
• NaOH Sodium Hydroxide
• NH3 - Ammonia

6
Bases Form Hydroxide Ions

• If the Hydroxide Ion is not already present in
  the Base, the base will make the Hydroxide ion by
  taking a Hydrogen ion from water.
• Bases are PROTON ACCEPTORS (they take a hydrogen
  ion)

(Water)
NH4
OH-

NH3

H
OH
?
7
More Info About Bases

• Anything with a high concentration of hydroxide
  ion is considered to be a base.
• Bases turn Red litmus paper BLUE

8
Can you tell the difference between an acid and a
base?

• Lets do a Lab to find out!

9
What is pH?

• The pH of a solution indicates its concentration
  of Hydronium Ions (H3O) or its concentration of
  Hydroxide Ions (OH-)
• pH is short for the power of Hydrogen
• Something with more (OH-) will be a base
• Something with more (H3O) will be an acid
• The pH scale ranges from 0-14

10
The Scale
Neutral
Lots of H3O
Lots of OH-

• 1 2 3 4 5 6 7 8 9 10 11 12 13 14

• In a neutral solution, the pH is 7
• The amount of H3O OH-
• Acids have a pH of less than 7
• The amount of H3O gt OH-
• Bases have a pH of greater than 7
• The amount of OH- gt H3O

11
Calculating pH

• Concentration is written as Molarity, or the
  number of moles per liter of solution
• Example the Hydronium concentration of pure
  water is 0.0000001 mol/L or 10-7 M
• This means that in one liter of water, we have
  0.0000001 mol of Hydronium ions

12
Calculating pH

• pH is the negative of the power of 10 used to
  describe the concentration of Hydronium ions
• Example
• hydronium concentration of
• pure water 10-7
• -(-7) pH of 7

13
Small Differences in pH Mean LARGE Differences in
Acidity

• Each number on the pH scale is a difference of a
  factor of 10
• pH of 2 is 10 times stronger than a pH of 3
• pH of 1 is 100 times stronger than a pH of 3
• Example problem the pH of apple juice is 3.
  the pH of coffee is 5. What is the acidity
  difference?
• There are 2 spaces between 3 and 5.
• 102 100 - Apple juice is 100 times more
  acidic than coffee

14
Review Questions

• Which ions do acids form in solution?
• H3O
• Which ions do bases form in solution?
• OH-
• Classify the following as acidic, basic, or
  neutral.
• Soap (pH 9)
• basic
• Sour liquid (pH 5)
• acidic
• Solution with 4x as many hydronium as hydroxide
  ions
• acidic
• Pure water
• neutral
• Arrange the following substances in order of
  increasing acidity vinegar (pH 2.8), gastric
  juices from your stomach (pH 2.0), soft drink
  (pH 3.4)
• Soft drink, vinegar, gastric juice

15

• Determine the pH of a 0.0001 M solution of HCl
• 0.0001 10-4 -(-4) pH of 4
• What is the pH of 0.01 M solution of HClO4,
  perchloric acid?
• 0.01 10-2 -(-2) pH of 2
• The concentration of hydronium ions in a certain
  acid is 10000 times the concentration of
  hydronium ions in a second acid solution. If the
  second solution has a pH of 6, what is the pH of
  the first solution?
• 10000 104 4 steps down pH scale 6-4 pH of 2
• Hand soap has a pH of 10. Drain cleaner has a pH
  of 14. How much more acidic is the hand soap
  than the drain cleaner?
• 4 steps 104 10,000 times more acidic

16
Can you find the pH of the solutions you just
tested?

• Lets do a lab to find out!