strong and weak acids and bases -...
TRANSCRIPT
Strong and Weak
Acids and Bases
Strength of Acids
CH3COOH CH3COO- + H+ Acetic acid
HF F- + H+ Weak Acids H2CO3 HCO3
- + H+
HCN CN- + H+
H2SO4 HSO4- + H+
HNO3 NO3
- + H+ Strong Acids HCl Cl- + H+
H3PO4 H2PO4- + H+
Moderate Acid Phosphoric acid
HCl is a Strong Acid
HF is a Weak Acid
Strong Bases
NaOH Na+ + OH-
KOH K+ + OH-
LiOH Li+ + OH-
Ba(OH)2 Ba2+ + 2 OH -
sparingly soluble in water
Weak Bases:
NH3 + H2O NH4+ + OH -
CH3COO- + H2O CH3COOH + OH -
CO32- + H2O HCO3
- + OH -
ammonia
acetate
carbonate
Acidity and Basicity of
Aqueous Solutions
HCl + H2O ----------> Cl- + [H3O]+
- +
Water is Amphoteric
NH3 + H2O ----------> NH4+ + [HO]-
+ -
Water can act as an acid or base. (It’s “amphoteric”)
H2O (l) + H2O (l) [H3O]+ (aq) + [HO]- (aq)
++
proton donor
proton acceptor
[ ]+ [ ]-
In pure water this “reaction” takes place to a very small extent. Concentration of hydronium ions = Concentration of hydroxide ions
[ H3O + ] = 1 x 10-7 = [ OH - ] = 1 x 10-7 M
A neutral solution is defined as a solution in which
[ H3O + ] = 1 x 10-7 M & [ OH - ] = 1 x 10-7 M
2. What is the hydronium ion concentration in a 1.0 M sulfuric acid solution?
A) 0.5 M B) 1.0 M
C) 1.5 M D) 2.0 M E) 4.0 M
1. What is the hydrogen ion concentration in a 1.0 M hydrochloric acid solution?
A) 0.5 M B) 1.0 M
C) 1.5 M D) 2.0 M E) 4.0 M
HCl ➜ H+(aq) + Cl-(aq)
H2SO4 ➜ 2 H+(aq) + SO4-(aq)
4. What is the hydroxide ion concentration in a 1.0 M calcium hydroxide solution?
A) 0.5 M B) 1.0 M
C) 1.5 M D) 2.0 M E) 4.0 M
3. What is the hydroxide ion concentration in a 1.0 M potassium hydroxide solution?
A) 0.5 M B) 1.0 M
C) 1.5 M D) 2.0 M E) 4.0 M
KOH ➜ K+(aq) + OH-(aq)
Ca(OH)2 ➜ Ca2+(aq) + 2 OH-(aq)
H+ H+ H+ H+ H+
OH-OH-OH-OH-OH-
[H+] 100 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14
[OH-] 10-14 10-13 10-11 10-9 10-7 10-5 10-3 10-1 100
[H+] vs [OH-]
Acidic Solution Basic Solution
H+ H+ H+ H+ H+
OH-OH-OH-OH-OH-
[H+] 100 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14
[OH-] 10-14 10-13 10-11 10-9 10-7 10-5 10-3 10-1 100
[H+] vs [OH-]
Ion Product of Water = Kw =[H3O+][OH-]=1.0 x 10-14
5. If the [H3O+] of a solution is 3.6 x10-8, what is the [OH-] ?
Kw =[H3O+][OH-]=1.0 x 10-14
(3.6 x10-8)[OH-]=1.0 x 10-14
[OH-]=(1.0 x 10-14)/(3.6 x10-8)
[OH-]=2.8 x10-7
6. If the [OH-] of a solution is 4.6 x10-4, what is the [H3O+] ?
Kw =[H3O+][OH-]=1.0 x 10-14
[H3O+](4.6 x10-4)=1.0 x 10-14
[H3O+]=(1.0 x 10-14)/(4.6 x10-4)
[H3O+] =2.2 x10-11
A neutral solution is defined as a solution in which
[ H3O + ] = 1 x 10-7 M & [ OH - ] = 1 x 10-7 M
An acidic solution is defined as a solution in which
[ H3O + ] > 1 x 10-7 M & [ OH - ] < 1 x 10-7 M
A basic solution is defined as a solution in which
[ H3O + ] < 1 x 10-7 M & [ OH - ] > 1 x 10-7 M
H+ H+ H+ H+ H+
OH-OH-OH-OH-OH-
[H+] 100 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14
[OH-] 10-14 10-13 10-11 10-9 10-7 10-5 10-3 10-1 100
[H+] vs [OH-]
ACIDIC BASIC
7. A solution with H3O+ concentration of 2 x 10–4 M can be described as
A) basic. B) acidic. C) neutral.
8. A solution with H3O+ concentration of 2.8 x 10–7 M can be described as
A) basic. B) acidic. C) neutral.
9. A solution with H3O+ concentration of 2.2 x 10–11 M can be described as
A) basic. B) acidic. C) neutral.
Because of the wide range of values for hydronium ion concentrations
(from 0.00000000000001 M to ≈ 100 M)
a logarithmic scale (the pH scale) is usually used.
The Log Function
H+ H+ H+ H+ H+
OH-OH-OH-OH-OH-
[H+] 100 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14
[OH-] 10-14 10-13 10-11 10-9 10-7 10-5 10-3 10-1 100
pH vs pOH
pH + pOH =14
pOH 14 13 11 9 7 5 3 1 0
pH 0 1 3 5 7 9 11 13 14
1 10-1
10. How many times more acidic is a solution with a pH of 1 (stomach acid) than a solution with a pH of 7 (blood)?
A) 6 B) 7 C) 7000 D) 1,000,000
11. How many times more basic is a solution with a pH of 12 (household ammonia) than a solution with a pH of 5 (coffee)?
A) 2.4 B) 7 C) 700 D) 10,000,000
pH = -log [H3O+]
pH = -log (1.0 x 10-3 )
pH = -(-3.00) = 3.00
12. What is the pH of 1.0 x 10-3 M HCl?
13. What is the pH of a solution if [H3O+] =2.6 x 10-10?
pH = -log [H3O+]
pH = -log (2.6 x 10-10 )
pH = -(-9.58) = 9.58
14. What is [H3O+] of a solution with a pH of 8.00?
[H3O+] = 10-pH
[H3O+] = 10-(8.00)
[H3O+] = 1.0 x 10-8 M
15. What is [H3O+] of a solution with a pH of 6.22?
[H3O+] = 10-pH
[H3O+] = 10-(6.22)
[H3O+] = 6.0 x 10-7 M
16. What is [OH–] in an aqueous solution with a pH of 10.34?
A) 4.6 x 10–11 M B) 2.2 x 10–4 M C) 4.6 x 103 M D) 2.2 x 1010 M E) 1.0 x 10–14 M
[H3O+] = 10-pH
[H3O+] = 10-(10.34)
[H3O+] = 4.6 x 10-11 M
Kw =[H3O+][OH-]=1.0 x 10-14
(4.6 x10-11)[OH-]=1.0 x 10-14
[OH-]=(1.0 x 10-14)/(4.6 x10-11)
[OH-]=2.2 x10-4
H+ H+ H+ H+ H+
OH-OH-OH-OH-OH-
[H+] 100 10-1 10-3 10-5 10-7 10-9 10-11 10-13 10-14
[OH-] 10-14 10-13 10-11 10-9 10-7 10-5 10-3 10-1 100
pOH 14 13 11 9 7 5 3 1 0
pH 0 1 3 5 7 9 11 13 14
ACIDIC BASIC
pH + pOH =14Ion Product of Water = Kw =[H3O+][OH-]=1.0 x 10-14
Buffers
Buffer System - A solution which resists a change in pH when small amounts of acid or base are added
Components of a Buffer System
A weak acid, and A weak base, and or A salt of that weak acid A salt of that weak base
17. Which of the following pairs of components would create a buffer solution ?
HCl and NaOH NaOH and NaCl KCl and NaCl
H2CO3 and NaHCO3 HF and KF
CH3COOH and CH3COO-Na+
How Does the Acetate Buffer System Work ?
1) An acetate buffer system contains CH3COOH and CH3COO - (acetic acid) (acetate anion)
2) The acetate anion reacts with excess acid (H+)
CH3COO - + H+ CH3COOH
3) The acetic acid component reacts with excess base (OH-)
CH3COOH + OH - CH3COO -
Buffer systems
A buffer contains significant amounts of a weak acid and its conjugate base. The acid consumes any added base, and the base consumes any added acid. In this way, a buffer resists pH change.
How Does the Acetate Buffer System Work ?
pH changes in pure water and a buffer solution
A comparison of the change in pH when 0.010 mol of acid and 0.010 mol of base are added to 1.0 L of pure water and to 1.0 L of 0.10 M acetic acid-0.10 M acetate ion buffer.
H2PO4-(aq) H+(aq) + HPO42-(aq)
H2CO3(aq) H+(aq) + HCO3-(aq)
Two Important Physiological Buffer Systems
The bicarbonate buffer system operates in the bloodstream.
The dihydrogen phosphate buffer system operates within cells.