Tuesday, May 11th:

1
(No Transcript)
2
(No Transcript)
3
Friday, April 26th A DayMonday, April 29th
B DayAgenda

• Section 15.1 Quiz What are Acids and Bases?
• Begin Section 15.2 Acidity, Basicity, and pH
• Self-ionization constant of H2O, Kw, neutral, pH,
  indicator
• Homework
• Practice pg. 541 1,2,4,5
• Practice pg. 544 1-4
• Concept Review Acidity, Basicity, and pH
• Next time
• Finish section 15.2/work day!

4
Section 15.1 QuizWhat are Acids and Bases

• This will be a stack behind the back quiz.
• Get in groups of 2-4.
• Working together, everyone in the group
• will complete their quiz.
• Once youre done, Ill shuffle them behind my
  back and sing a song until you tell me to stop.
• The quiz on top is the only one Ill grade and
  everyone in that group will get that grade.

5
Self-Ionization of Water

• Water can act as either an acid or a base.
• This means that a water molecule can
• either give or receive a proton.

• Base Acid
  Conjugate Acid Conjugate Base
• A pair of water molecules are in equilibrium with
  two ionsa hydronium ion and a hydroxide ionin a
  reaction known as the self-ionization of water.

6
Self-Ionization of Water
Base Acid
Conjugate Acid Conjugate Base

• The equilibrium expression for this reaction is
• Keq H3OOH-
• This equilibrium constant, called the
• self-ionization constant, is so important
• that it has a special symbol, Kw.
• The self-ionization of water reaction is an
  additional reaction that runs in the background.

7
Self-Ionization of Water
Base Acid Conjugate Acid Conjugate Base

• In pure water, the two ions have the same
  concentration.
• Experiments show that this concentration is1.00
  10-7 M at 25C.
• H3O OH- 1.00 10-7 M
• Since Kw H3O OH-, then
• Kw 1.00 X 10-14

8
Self-Ionization of Water

• The product of these two ion concentrations is
  always a constant.
• Anything that increases one of the ion
  concentrations will decrease the other.
• If you know one of the ion concentrations, you
  can calculate the other using the constant Kw.

9
Sample Problem A, pg. 541Determining OH- or
H30 using Kw

• What is the OH- in a 3.00 X 10-5 M solution of
  HCl?
• HCl is a strong acid and ionizes completely
• HCl (g) H2O (l) H3O (aq) Cl- (aq)
• 3.00 X 10-5 M 3.00 X 10-5 M
• Because 11 ratio, HCl H3O 3.00 X 10-5 M
• Kw OH- H3O 1.00 X 10-14
• 1.00 X 10-14 OH- (3.00 X 10-5 M)
• OH- 3.33 X 10-10 M

10
Additional Practice

• What is the H3O in a solution of NaOH whose
  concentration is 3.75 X 10-2 M?
• NaOH is a strong base and ionizes completely
• NaOH (s) Na (aq) OH- (aq)
• 3.75 X 10-2 M 3.75 X 10-2 M
• Because 11 ratio, NaOH OH- 3.75 X 10-2 M
• Kw OH- H3O 1.00 X 10-14
• 1.00 X 10-14 3.75 X 10-2 M H3O
• H3O 2.67 X 10-13 M

11
pH and Acidity

• When acidity and basicity are exactly balanced
  such that the numbers of H3O and OH- ions are
  equal, we say that the solution is neutral.
• Pure water is neutral because it contains equal
  amounts of the two ions.

12
Acidity/Basicity

• The concentration of hydronium ions (H3O) in a
  solution expresses its acidity.
• The concentration of hydroxide ions (OH-) in a
  solution expresses its basicity.

13
Measuring pH

• The letters p and H stand for power of
  hydrogen.
• pH can be calculated by the following
  mathematical equation
• pH -log H3O

14
Calculating pH Example 1

• What is the pH if H3O 3.5 X 10-4 M?
• pH - log H3O
• pH - log (3.5 X 10-4 )
• pH 3.5 (2 sig figs)

15
Calculating pH Example 2

• What is the pH if OH- 5.0 X 10-5 M?
• pH - log H3O
• Kw OH- H30 1.00 X 10-14
• 1.00 X 10-14 (5.0 X 10-5 M) H3O
• H3O 2.0 X 10-10 M
• pH - log (2.0 X 10-10 )
• pH 9.7 (2 sig figs)

16
Sample Problem B, pg. 544Calculating pH for an
Acidic or Basic Solution

• What is the pH of (a) a 0.00010 M solution of
  HNO3, a strong acid, and (b) a 0.0136 M solution
  of KOH, a strong base?
• (a) HNO3 is a strong acid and ionizes
  completely
• HNO3 (g) H2O (l) ? H3O (aq) NO3- (aq)
• 0.00010 M 0.00010 M
• Because 11 ratio, HNO3 H3O 0.00010 M
• pH -log H3O
• pH -log (0.00010)
• pH 4.0 (2 sig figs)

17
Sample Problem B, continued

• What is the pH of (a) a 0.00010 M solution of
  HNO3, a strong acid, and (b) a 0.0136 M solution
  of KOH, a strong base?
• (b) KOH is a strong base and ionizes completely
• KOH (s) ? K (aq) OH- (aq)
• 0.0136 M 0.0136 M
• Because 11 ratio, KOH OH- 0.0136 M
• Kw OH- H30 1.00 X 10-14
• 1.00 X 10 -14 (0.0136 M) H30
• H30 7.35 X 10-13
• pH - log H30 pH - log (7.35 X 10 -13)
• pH 12.1 (3 sig figs)

18
Measuring pH

• Because of the negative sign, as the hydronium
  ion concentration increases, the pH will
  decrease.
• A solution of pH 0 is very acidic.
• A solution of pH 14 is very basic (alkaline).
• A solution of pH 7 is neutral.

19
pH values of some common materials
20
Indicators

• Certain dyes, known as indicators, turn different
  colors in solutions of different pH.
• An indicator is a compound that can reversibly
  change color depending on the pH of the solution
  or other chemical change.

21
pH Meters

• A pH meter is an electronic instrument equipped
  with a probe that can be dipped into a solution.
• The probe has two electrodes, one of which is
  sensitive to the hydronium ion.
• An electrical voltage develops between
• the two electrodes, and the circuitry
• measures this voltage.
• The instrument converts the measurement into a pH
  reading, which is displayed on the meters
  screen.

22
Indicators vs. pH Meters

• Indicators
• Quick and convenient
• Do not give very precise results
• pH Meters
• Very precise
• More complicated and expensive
• or

23
Homework

• Practice pg. 541 1,2,4,5
• Practice pg. 544 1-4
• Concept Review Acidity, Basicity, and pH
• Next time
• Finish section 15.2 and work day!