Post on 20-Jan-2016
Acid-BaseAcid-BaseEquilibriaEquilibria
Chapter 16Chapter 16
Acids
1. Have a sour taste. e.g., Vinegar, lemons, limes, sour milk
2. Cause litmus to change from blue to red.
4. Acid solutions conduct electricity.
3. Acids neutralize bases.
1. Have a bitter taste. e.g., caffeine, walnuts, soap
3. Feel slippery. Many soaps contain bases.
Bases
5. Basic solutions conduct electricity.
2. Cause litmus to change from red to blue.
4. Bases neutralize acids.
Arrhenius acid - a substance that produces H+ (H3O+) in water
Arrhenius base - a substance that produces OH- in water
Theory is restricted to aqueous solutions
Brønsted acid - a proton donorBrønsted base - a proton acceptor
acid acid base
acidconjugate
basebase conjugate
acid
base
Conjugate pairs differ by a proton
• Water acts as a Brønsted-Lowry base and abstracts a proton (H+) from the acid.
• As a result, the conjugate base of the acid and a hydronium ion are formed.
Fig 16.2
HCl + H2O → Cl− + H3O+
O
H
H + O
H
H O
H
H H OH-+[ ] +
Acid-Base Properties of Water
H2O (l) H+ (aq) + OH- (aq)
H2O + H2O H3O+ + OH-
acid conjugate
base
base conjugate
acid
autoionization of water
H2O (l) H+ (aq) + OH- (aq)
The Ion Product of Water
Kc =[H+][OH-]
[H2O][H2O] = constant
Kc[H2O] = Kw = [H+][OH-]
Ion-product constant (Kw) - the product of the molar concentrations of H+ and OH- ions at a particular temperature.
At 25°C:Kw = [H+][OH-] = 1.0 x 10-14
[H+] = [OH-]
[H+] > [OH-]
[H+] < [OH-]
Solution is:
neutral
acidic
basic
What is the concentration of OH- ions in a HCl solution whose hydrogen ion concentration is 1.3 M?
Kw = [H+][OH-] = 1.0 x 10-14
[H+] = 1.3 M
[OH-] =Kw
[H+]
1 x 10-14
1.3= = 7.7 x 10-15 M
pH – A Measure of Acidity
pH = −log [H+]
[H+] = [OH-]
[H+] > [OH-]
[H+] < [OH-]
Solution is:
neutral
acidic
basic
[H+] = 1 x 10-7
[H+] > 1 x 10-7
[H+] < 1 x 10-7
pH = 7
pH < 7
pH > 7
At 25°C
pH [H+]
pH = −log [H3O+]
pOH = -log [OH-]
[H+][OH-] = Kw = 1.0 x 10-14
-log [H+] – log [OH-] = 14.00
pH + pOH = 14.00
Fig 16.5 H+ concentrations and pH of common substances
The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H+ ion concentration of the rainwater?
pH = -log [H+]
[H+] = 10-pH = 10-4.82 = 1.5 x 10-5 M
The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood?
pH + pOH = 14.00
pOH = -log [OH-] = -log (2.5 x 10-7) = 6.60
pH = 14.00 – pOH = 14.00 – 6.60 = 7.40
AcidsandBases
Other “p” Functions
The “p” in pH tells us to take the negative base - 10 logarithm of the quantity (in this case, hydronium ions)
Some similar examples:
pOH = -log [OH−]
pKw = -log Kw
pCl = -log [Cl−]
AcidsandBases
For less accurate measurements:Litmus paper
“Red” paper turns blue above ~pH = 8 “Blue” paper turns red below ~pH = 5
Indicator:
AcidsandBases
For more accurate measurements: pH meter, which measures the voltage in the solution
Fig 16.6 Digital pH meter