Chapter 8 - Monoprotic Acid-Base Equilibria

Question 1

Ka and pKa
pKa = - logKa

1. As K increase, pka _____
2. strong acids have _____ pka and strong base of ____ pka

Answer 1

1. decrease

2. small, large

Question 2

Ka’s and pKa’s

1. Different groups (protons) have …….
2. The more acidic ones will have ____ pKa’s than the more basic ones.

Answer 2

1. different pKa’s

2. lower

Question 3

Strong Acids
The concentration of ____ is equal to the concentration of the ______

Strong acid ______ ionize

autoionization of water is ____ _____ compared to the acid

Answer 3

H3O+, strong acid

completely

negligible small

Question 4

Weak acids
Weak acids ______ _______ ionize

The autoionization of water is ___ ___ negligible

How to solve for pH?

Answer 4

don’t completely

no longer

ICE Table

Question 5

Fraction of dissociation (alpha):

For weak acid, always assume that ____ = _____ = ______ the weak base is the opposite (what is it)

Answer 5

Fraction of the acid in form A- and H+

[H+] = [A-] = x, [OH-] = [BH+] = x

Question 6

When concentrations are ______ (>10^6), use _____

when concentrations are ______(<10^-8), the pH is _______ because you have _______

Answer 6

high, -log

low, 7.00, water

Question 7

Resist changes in pH by when acids or bases are added or when dilutions occur

Answer 7

Buffers

Question 8

Buffers contains (2)

A buffer must contain significant amounts of both and not just one. Within….

Answer 8

significant amount of weak acid and conjugate base. significant amount of weak base and conjugate acid

factor of 10

Question 9

what is Henderson-Hasselbach (HH)

Small x approximation must be valid:
The is small when:
1. the initial concentration of …….
2. The equilibrium is fairly….

Answer 9

A calculations of pH of a buffer

Allows quick calculation of pH for buffers

1. acid and/or bases not too dilute
2. small

Question 10

Buffer Effectiveness

1. The best buffer is when pH =
   - what that region called in titration curve when this occurs?
2. what is the best buffer in terms of pKa
3. Useful range for pH

Answer 10

1. pKa
   - buffer region
2. pKa that is close to desired pH
3. ±1

Question 11

Buffer Effectiveness

1. Adding a small amount of strong acid to buffer:
   - what does stoichiometrically converts ______ and ________ thus pH _____
2. Adding small amount of strong base to buffer
   - what does stoichiometrically converts ______ and _____ thus pH ______

Answer 11

1. base to conjugate acid thus decreasing the pH

2. amount of acid to conjugate base thus increasing the pH

Question 12

how can a buffer get destoryed?

when can a buffer become effective?

• concentration should not differ by more than a ____ ______ ______
• what happen if too much base and acid added?

what is another way a buffer can become effective?

• what happen if the buffer is concentrated enough?
• what does this causes the capacity to do?

Answer 12

adding too much acid and/or base

concentration of acid and conjugate base are equal

• factor of 10
• pH will alter too much

concentration of acid and conjugate base are high

• pH resist change
• surpass capacity

Question 13

Buffers - exceptions

Activity coefficients should be used in Henderson-Hasselbalch however ____ _____.
If activity deviates a lot (look at ionic strength), then you may need to ____ _____.

If the concentration of HA or A- is ____ or if H+ or OH- is ___, then approximations _______
Strong acid = OH- is probably negligible.

Answer 13

usually exculded
include them

small, large, will not work

Question 14

Measure how well a solution resists changes in pH when strong acid and bases are added

Answer 14

Buffer capacity (β)