Acid Base Equilibria. Dr. Harris Ch 20 Suggested HW : Ch 20: 5, 9, 11 *, 19*, 21, 29**, 35, 56 ** * Use rule of logs on slide 10 ** Use K a and K b tables in ch 20 text. . Introduction.
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Suggested HW: Ch 20: 5, 9, 11*, 19*, 21, 29**, 35, 56**
* Use rule of logs on slide 10
** Use Ka and Kb tables in ch 20 text.
H+aq + X-aq
M+aq + OH-aq
H3O+(aq) + OH−(aq)Autoionization of Water
A strong acid completely transfers its protons into water. Its conjugate base has a negligible tendency to be protonated.
A weak acid partially dissociates, and so it exists as a mixture of molecules and ions. The conjugate of a weak acid/base is a weak base/acid
HCl(aq) + H2O(l) H3O+(aq) + Cl−(aq)
The position of equilibrium is always favored in the direction that forms the weaker acid/base.
* at 25oC
An acidicsolutionis defined as one in which [H3O+] > [OH-] (pH < 7)
A neutral solution is defined as one in which [H3O+] = [OH-] (pH = 7)
A basicsolution is defined as one in which [OH-] > [H3O+] (pH > 7)
Also, please note that H+ and H3O+ plus are the same, and may be used interchangeably in the book.
this will come in handy
.040M .040M .040M
.028M .028M .028M
HCOOH (aq)+ H2O(L) H3O+(aq) + HCOO-(aq)
I .40 M 0 0
C -x +x +x
E .40-x x x
CH3COOH (aq)+ H2O(L) H3O+(aq) + CH3COO-(aq)
Calculate the pH of a 0.050 M acetic acid solution given that Ka = 1.8 x 10-5M
1. We set up the ICE table to determine the concentration of H3O+
CH3COOH (aq) + H2O(L) H3O+(aq) + CH3COO-(aq)
2. Solve for x. We see that Ka is very small because CH3COOH is a weak acid.
3. Calculate pH
Use this method when K < 10-4
Example: Determine the pH of a 0.75 M hydroxylamine, HONH2(aq) solution given that Kb = 8.7 x 10-9 M
HONH2 (aq) + H2O(L) HONH3+ (aq) + OH-(aq)
1. We can write out the equilibrium expression showing the base protonation.
2. Set up ICE table
3. Solve x
4. THIS IS A BASE. That means that you must calculate pOH FIRST. Then, determine pH.
Neutral cations are the cations of strong bases.
Neutral anions are the anions of strong acids.
Basic anions are the conjugate bases of weak acids.
Acidic cations are the conjugate acids of weak bases, and hydrated metal ions, as shown on pg 760.
1.) We first have the initial deprotonation. Because sulfuric acid is a strong acid, you can assume that all of it is dissociated at equilibrium.
2.) Now, we have the second deprotonation. Use the concentrations of H3O+ and HSO4- from above as your initial values. Use pKa values from the table to determine the final concentration of [H3O+]