Sample solution in the image. Compute for the pH, pOH, and [OH-] of a buffer solution that is 0.20 M in acetic acid and contains sufficient sodium acetate to make the acetate ion equal to 0.05 M. Ka = 1.85 x 10^-5.

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Sample solution in the image. Compute for the pH, pOH, and [OH-] of a buffer solution that is 0.20 M in acetic acid and contains sufficient sodium acetate to make the acetate ion equal to 0.05 M. Ka = 1.85 x 10^-5.
Henderson- Hasselbalch Equation
-use without using equilibrium equations, [H°] [OH]
-use only for initial concentration w/ ka| kb & Ca & Cb
In buffer pair of weak acid and its corresponding base, ionization takes place. The pH
of solution consisting weak acid is related to its dissociation constant (k).
HA +H* + A
Weak Acid CA
CB
@equilibrium Ka = [H*] [A*]
[HAJ
Log Ka = log (H°] [A"]
[HA]
Log Ka = log[H*] + log [A^)_
[HA]
- Log = log (H*] + log [A"]
(HA]
pka = pH - log base/ acid
pH = pKa - log acidic component
basic component
Module II
82
MODULE III
CHEMICAL EQUILIBRIUM AND IONIC EQUILIBRIUM
or pH = 14- pkb -log acidic component
basic component
pH = 14- pKb -log acidic component
basic component
pH = pkw- pKb + log base/salt
Sample problems:
1. Compute for the pH, pOH, and [OH-] of a buffer solution that is 0.20 M in acetic
acid and contains sufficient sodium acetate to make the acetate ion equal to 0.1 M.
Ka - 1.85 x 105
Solution:
HAC++ H*+ AC
НАС
Ac
Initial
0.2
0.1
Change
+x
+X
Equilibrium
0.2 -x
0.1+x
Ka = 0.1 x + X = 1.85 x 105
0.2 -x
[H'] = 3.7 x 10-5
pH =4.4
[OH] -2.7 x 10 10
Another solution
HHE
pH = pka + log (A]
[HAJ
pH = -log 1.85 x10-5 + log 0.1 - 4.4
0.2
Transcribed Image Text:Henderson- Hasselbalch Equation -use without using equilibrium equations, [H°] [OH] -use only for initial concentration w/ ka| kb & Ca & Cb In buffer pair of weak acid and its corresponding base, ionization takes place. The pH of solution consisting weak acid is related to its dissociation constant (k). HA +H* + A Weak Acid CA CB @equilibrium Ka = [H*] [A*] [HAJ Log Ka = log (H°] [A"] [HA] Log Ka = log[H*] + log [A^)_ [HA] - Log = log (H*] + log [A"] (HA] pka = pH - log base/ acid pH = pKa - log acidic component basic component Module II 82 MODULE III CHEMICAL EQUILIBRIUM AND IONIC EQUILIBRIUM or pH = 14- pkb -log acidic component basic component pH = 14- pKb -log acidic component basic component pH = pkw- pKb + log base/salt Sample problems: 1. Compute for the pH, pOH, and [OH-] of a buffer solution that is 0.20 M in acetic acid and contains sufficient sodium acetate to make the acetate ion equal to 0.1 M. Ka - 1.85 x 105 Solution: HAC++ H*+ AC НАС Ac Initial 0.2 0.1 Change +x +X Equilibrium 0.2 -x 0.1+x Ka = 0.1 x + X = 1.85 x 105 0.2 -x [H'] = 3.7 x 10-5 pH =4.4 [OH] -2.7 x 10 10 Another solution HHE pH = pka + log (A] [HAJ pH = -log 1.85 x10-5 + log 0.1 - 4.4 0.2
Sample Problems
1.Calculate the hydroxide ion concentration of a solution that is 0.1 F with NH3 and
0.25F with respect to (NH,)2SO4.
Reaction
NH3 + NH, + OH
NH3
NH4 *
OH-
initial
0.1
0.5
change
equilibrium
-X
+X
+X
0.1 - x
0.5 + X
Solution:
If (NH4)2SO4
0.25
- 2 NH4 *
2(0.25)
SO, 2
Ка 3D (0.5 + х) (х) %3D1.75 х 10 -5
(0.1 + x)
* x is negligible, Use Rule of 100
*If C/K is greater than 100 then x is negligible
(x)
3.5 x 10-6 = (OH1)
Transcribed Image Text:Sample Problems 1.Calculate the hydroxide ion concentration of a solution that is 0.1 F with NH3 and 0.25F with respect to (NH,)2SO4. Reaction NH3 + NH, + OH NH3 NH4 * OH- initial 0.1 0.5 change equilibrium -X +X +X 0.1 - x 0.5 + X Solution: If (NH4)2SO4 0.25 - 2 NH4 * 2(0.25) SO, 2 Ка 3D (0.5 + х) (х) %3D1.75 х 10 -5 (0.1 + x) * x is negligible, Use Rule of 100 *If C/K is greater than 100 then x is negligible (x) 3.5 x 10-6 = (OH1)
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