1. ACID Properties, Definitions & Finding H+ for Strong and Weak Acids and Bases
Søren Sørensen

2. Properties of acids pH < 7
How do we recognize acids?
pH < 7
Turn blue litmus paper red (Blue to Red = A-CID!)
Taste sour
Corrosive (gradual destruction of a substance, usually metal, by chemical reaction)
React with active metals to form hydrogen gas
Conduct electricity
React with hydroxides (bases) to form water and a salt 2

3. Properties of bases pH > 7 Turn red litmus blue (Basic Blue)
How do we recognize bases?
pH > 7
Turn red litmus blue (Basic Blue)
Taste bitter, chalky
Feel slippery
Caustic (capable of burning/destroying living tissue)
Conduct electricity
React with acids to form water and a salt 3

4. Acid/Base Definitions
Arrhenius Model-
Acids produce hydrogen ions in aqueous solutions
Bases produce hydroxide ions in aqueous solutions
Bronsted-Lowery Model-
Acids are proton donors
Bases are proton acceptors
Lewis Acid Model-
Acids are electron pair acceptors
Bases are electron pair donors

5. The H atom loses an electron
Acid- Base Theory
1st-What does a H atom look like?
1 Proton and 1 electron
2nd- When a Hydrogen ion, H+,
forms, what happens?
The H atom loses an electron
So H+ = a proton
BUT
In an aqueous solution,
A H+ or proton rides piggy back on a water molecule as H3O+, a HYDRONIUM ion. .
Soo….
PROTONS, HYDROGEN IONS AND HYDRONIUM IONS
are ALL interchangeable.

6. Let’s play a game called: WATCH THE PROTON!!
Bronsted-Lowry Theory:
Acids donate protons, and
Bases accept protons.
Proton donor
HA B  HB
+ A-
acid
base
Conjugate
acid
Conjugate
base
Proton acceptor
Why is HB the conjugate acid?
Proton donor
HA B  HB
+ A-
Conjugate
acid
Conjugate
base
Consider the reverse reaction:
Proton acceptor

7. How about Bases? Ex. NaOH, LiOH, KOH
Strong Bases are Alkali metals combined with OH-
Ex. NaOH, LiOH, KOH
WEAK BASES have Carbon and Hydrogen combined with
N, NH, or NH2
Ex. C6H6NH2, CH3NH2

8. Again-WATCH THE PROTON between water and methyl amine (a WEAK base)
acid
Proton donor
Water donates a proton.
Conjugate
base
H2O + CH3NH2 
CH3NH3+ + OH-
base
Proton acceptor
METHYL AMINE accepts the proton
and therefore is a BASE!
Conjugate
acid

9. You try… 1. In the following reaction, identify the acid –base pairs!
HBr + NH3  NH Br –
2. What is the conjugate base of H2S?
3. What is the conjugate acid of NO3 -?
HS-
HNO3

10. KNOW: THE STRONGER THE ACID, THE WEAKER IT’S CONJUGATE BASE and vice versa!
Question What is the strongest base in this reaction? HNO3 + H2O  NO3- + H3O+
ANS: H2O is the strongest base. Strong acids, such as HNO3
have weak conjugate bases
So NO3- is a weak base. NO3- and H2O compete
for the H+ and water WINS
most of the time as this reaction goes to completion.

11. Of the following acids, determine
A) the strongest acid
B) the acid that produces the lowest concentration of hydronium ions per mole of acid
C) The acid with the strongest conjugate base
D) The strong acid
E) The acid with the weakest conjugate base
Iodic
H2O2
H2O2
ALL of these are WEAK!
Iodic

12. Amphoteric Compounds…
… behave either as an acid or a base.
Water is the most common amphoteric compound.

13. Thus- the Equilibrium constant for water = Kw
AUTOIONIZATION
H2O can function as both an ACID and a BASE.
Thus- the Equilibrium constant for water = Kw
Kw = [H3O+] [OH-] =
1.00 x at 25 oC

14. Thus, for ANY Aqueous Solution,
[H3O+][OH-]= 1 x 10-14
Use this relationship to find
[OH-]
in an acid solution
Use this relationship to find
[H+]
in a basic solution
Variation of Kw with Temperature

16. Acid is electron-pair acceptor. Base is an electron-pair donor.
Lewis Theory
Gilbert N. Lewis – U.S.
Acid is electron-pair acceptor.
Base is an electron-pair donor.
BF NH3  BF3NH3
To make bond
F H F H
F-B :N-H  F - B – N-H
Acid base
Electron pair

17. Two for You:
In the following reaction, which substance is the Lewis acid and which is the Lewis base? Cl- + BCl3BCl4 ?
Which of the following would make the best Lewis base?
HNO3
NH4+
PH3
LiOH

18. SUMMARY:- there are Three models of acids:
l. ARRHENIUS MODEL
Basis for the model--action in water
* acid definition: produces H+ in water solution
* base definition: produces OH1- in water solution
2. BRONSTED-LOWRY MODEL
Basis for the model-- proton transfer
* acid definition: donates a proton ( H+ )
* base definition: accepts a proton
* conjugate acid definition: the acid becomes the conjugate
base after it donates the proton because it can now accept it back.
conjugate base definition: the base becomes the conjugate
acid after it accepts the proton because it can now donate it back.
3. LEWIS MODEL
Basis for model--electron pair transfer
* acid definition: accepts a pair of electrons
* base definition: donates a pair of electrons

19. ALL OTHER ACIDS ARE WEAK!!!

20. ALL OTHER BASES ARE WEAK
ALL OTHER BASES ARE WEAK!!! Organic Weak Bases generally have -NH2, -NH, or -N

21. Acid Ionization

22. Dissociation of Strong Acids
Strong acids are strong electrolytes that, for practical purposes, are assumed to ionize completely in water
ANIMATION
Youtube
HCl(aq ) + H2O(l ) -> H3 O+ (aq ) + Cl-1 (aq )
HNO3 (aq ) + H2O(l ) -> H3 O+ (aq ) + NO3-1 (aq )
HClO4 (aq ) + H2O(l ) -> H3 O+ (aq ) + ClO4-1(aq )
H2SO4 (aq ) + H2O(l ) -> H3 O+ (aq ) + HSO4-1(aq )

23. Acid Dissociation Acid Proton Conjugate base For a STRONG acid
HA  H A-
Acid Proton Conjugate
base
For a STRONG acid
NO HA exists,
therefore
Ka is INFINITE!
Alternately, H+ may be written in its hydrated form, H3O+ (hydronium ion)

24. FINDING the [H+] Concentration of a STRONG ACID
Because a strong acid- 100% dissociates, the [H+] concentration is the SAME as the concentration of the ACID!! 0.05M HCl [H+] = 0.05 M .55 M HNO3 [H+] = 0.55 M 1.5 M H2SO4 [H+] = 3.0 M
Bottom line, for strong acids [acid] = [H+]

25. Dissociation of Weak Acids
Weak acids, only ionize to a limited extent in water. FORM AN EQUILIBRIUM.
Large Ka or small Ka?
ANIMATION
Video
HNO2(aq) + H2O(l) H3O+(aq) + NO2-1(aq)

26. Dissociation Constants for Weak Acids
Formula
Conjugate Base Ka
 Iodic 
 HIO3 
 IO3- 
 1.7 x 10-1 
 Oxalic 
 H2C2O4 
 HC2O4- 
 5.9 x 10-2 
 Sulfurous 
 H2SO3 
 HSO3- 
 1.5 x 10-2 
 Phosphoric 
 H3PO4 
 H2PO4- 
 7.5 x 10-3 
 Citric 
 H3C6H5O7 
 H2C6H5O7- 
 7.1 x 10-4 
 Nitrous 
 HNO2 
 NO2- 
 4.6 x 10-4 
 Hydrofluoric 
HF 
 F- 
 3.5 x 10-4 
 Formic 
 HCOOH 
 HCOO- 
 1.8 x 10-4 
 Benzoic 
 C6H5COOH 
 C6H5COO- 
 6.5 x 10-5 
 Acetic 
 CH3COOH 
 CH3COO- 
 1.8 x 10-5 
 Carbonic 
 H2CO3 
 HCO3- 
 4.3 x 10-7 
 Hypochlorous 
 HClO 
 ClO- 
 3.0 x 10-8 
 Hydrocyanic 
 HCN 
 CN- 
 4.9 x 10-10 
The larger
Ka, the
Stronger
WEAK acid
it is!
Also, the
larger Ka,
The
Weaker
It’s
Conjugate
base

27. Finding the [H+] of a WEAK Acid
What is the [H+] of a 0.50 M solution of acetic acid, HC2H3O2, Ka = 1.8 x 10-5 ?
Step #1: Write Equilibrium
Step #2: ICE it!
HC2H3O2  C2H3O H+ I C E
0.50
- x
+ x
+ x x x x

28. FINDING [H+] FOR WEAK ACID
SUBSTITUTE INTO Ka EXPRESSION
ASSUME X is small compared to 0.5
SOLVE FOR X
[H+] = 3.0 x 10-3 M

29. Percent Ionization Percent Ionization = 3 x 10-3M /.5M X 100% = 0.6%
What this means is-- if I had 100 molecules of this weak acid, .6 would ionize or exist as ions in aqueous solution. A VERY, VERY WEAK ACID!

30. What about BASES you ask? Base Ionization

31. Dissociation of Strong Bases
MOH(s)  M+(aq) + OH-(aq)
Strong bases are soluble metallic hydroxides
Group I hydroxides (NaOH, KOH) are very soluble
Group II hydroxides (Ca, Ba,Sr) are less soluble
All weak bases are generally INSOLUBLE! NH3 is most soluble Weak Base

32. The [OH-] of strong bases is calculated directly from the concentration of the base in solution (just like strong acids)
The [OH-] Concentration of a STRONG BASE Solution is EQUAL to the Concentration of the STRONG BASE.
ACID [OH-]
0.15 M NaOH M
1.43 M KOH M
.0017M Ca(OH) M

33. Reaction of Weak Bases with Water
The base reacts with water, producing its conjugate acid and hydroxide ion:
CH3NH2 + H2O  CH3NH3+ + OH- Kb = 4.38 x 10-4
NOTE: For a Basic disssociation,
you MUST have H2O as a reactant!!

34. Reaction of Weak Bases with Water
The generic reaction for a base reacting with water, producing its conjugate acid and hydroxide ion:
B + H2O  BH+ + OH-
(Yes, all weak bases do this – DO NOT
endeavor to make this complicated!)

35. Kb for Some Common Weak Bases
Many students struggle with identifying weak bases and their conjugate acids.
What patterns do you see that may help you?
Base
Formula
Conjugate Acid Kb
Ammonia 
 NH3
 NH4+
 1.8 x 10-5 
 Methylamine
 CH3NH2
 CH3NH3+
 4.38 x 10-4 
 Ethylamine
 C2H5NH2
 C2H5NH3+
 5.6 x 10-4 
 Diethylamine
 (C2H5)2NH
 (C2H5)2NH2+
 1.3 x 10-3 
 Triethylamine
  (C2H5)3N
  (C2H5)3NH+
 4.0 x 10-4 
 Hydroxylamine
 HONH2 
 HONH3+  
 1.1 x 10-8 
 Hydrazine
H2NNH2 
H2NNH3+  
 3.0 x 10-6 
 Aniline
 C6H5NH2 
 C6H5NH3+  
 3.8 x 10-10 
 Pyridine
 C5H5N 
 C5H5NH+  
 1.7 x 10-9 

36. A Weak Base Equilibrium Problem
What is the [H+] of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?
Step #1: Write the equation for the reaction
NH3 + H2O  NH4+ + OH-

37. A Weak Base Equilibrium Problem
What is the [H+] of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?
Step #2: RICE it!
NH3 + H2O  NH OH-
0.50 I C E
- x +x +x x x x

38. A Weak Base Equilibrium Problem
What is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?
Step #3: Set up Kb expression
NH3 + H2O  NH4+ + OH- E x x x
Step #3b: Make an assumption!
As2

39. A Weak Base Equilibrium Problem
What is the [H+] of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?
Step #4: Solve for x, which is also [OH-]
NH3 + H2O  NH4+ + OH- E x x x
[OH-] = 3.0 x 10-5 M
[OH-] [H+]= 1 x M
[3.0 x 10-5] [H+]= 1 x M
[H+] = 3.3 x M

40. pH + pOH = 14 pH = -log10(H3O+) pOH = -log10(OH-) [H3O+] = 10-pH
Calculating pH, pOH
pH = -log10(H3O+)
pOH = -log10(OH-)
Relationship between pH and pOH
pH + pOH = 14
Finding [H3O+], [OH-] from pH, pOH
[H3O+] = 10-pH
[OH-] = 10-pOH

41. pH and pOH Calculations

42. A Weak Base Equilibrium Problem
What is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?
Step #5: Convert [OH-] to pH
NH3 + H2O  NH4+ + OH- E x x x

43. Graphic: Wikimedia Commons user Slower

44. Let’s Practice!

45. Answers
Notice(comes in handy!!): pH is always 1 less than power of ten of [H+]
pOH is always 1 less than power of ten of [OH-]
Always check: [H+][OH-] should equal 1 x or 10 x 10-15!

46. NOW Another Typical Weak BASE Equilibrium Problem
What is the pH of a 0.50 M solution of aniline, C6H5NH2, Kb = 7.4 x ?
Step #1: Write the dissociation equation
C6H5NH2 + H2O  C6H5NH3+ + OH-
NOTE: For a Basic disssociation,
you MUST have H2O as a reactant!!

47. A Weak Acid Equilibrium Problem
What is the pH of a 0.50 M solution of aniline, C6H5NH2, Kb = 7.4 x ?
Step #2: ICE it!
C6H5NH C6H5NH OH- I C E
0.50
- X +X +X X X X

48. A Weak Acid Equilibrium Problem
What is the pH of a 0.50 M solution of aniline, C6H5NH2, Kb = 7.4 x ?
Step #3: Set up the law of mass action
C6H5NH2 + H2O  C6H5NH3+ + OH- E x x x

49. A Weak Acid Equilibrium Problem
What is the pH of a 0.50 M solution of aniline, C6H5NH2, Kb = 7.4 x ?
Step #4: Solve for x, which is also [OH-]
C6H5NH2 + H2O  C6H5NH3+ + OH- E x x x
[OH-] = 1.92 x 10-5 M

50. A Weak Acid Equilibrium Problem
What is the pH of a 0.50 M solution of aniline, C6H5NH2, Kb = 7.4 x ?
Step #5: Convert [OH-] to pOH
Convert pOH to pH!!
DONE!!!!