Class 5 Flashcards
Is an acid more or less stable with the proton?
Without (think quarterback analogy–wants to give up the ball to reduce stress)
Is a base more or less stable with the proton?
With (think wide receiver analogy–unstable and stressed until receives the ball)
What is a better definition of acids/bases (Lewis or Bronsted)?
Lewis! Bases donate e-, are nucleophiles Acids accept e-, are electrophiles
Acids generally have ______ electronegative atoms bonded to H and bases generally have _____ electronegative atoms with lone pairs.
Acids = more EN atoms Bases = less EN atoms
Atoms without H can be acids if…
Electron deficient or with large positive charges
What is the KEY thing to have to be a base?
A lone pair!
What is it called when a compound has an acidic and basic functional group?
Amphoteric; can act as an acid or a base
Does size affect acid and base strength?
Yes. Acids are stronger if larger Bases are stronger if smaller
Rules for ranking acids/bases?
- Same structure, different charge: more charged acid/base will be stronger 2. Same row: more (acid)/less (base) EN will be stronger 3. Same column: larger (acids)/smaller (bases) size will be stronger
Do stronger acids favor the products or reactants?
Products. They dissociate more completely.
Do stronger bases favor the products or reactants?
Products. They “associate” more completely.
Do weak acids favor reactants or products?
Reactants
Do weak bases favor reactants or products?
Reactants
Ka > 1 means what?
Favors products (strong acid or strong base)
A strong acid will produce a _______ conjugate base
weak
Ka
Favors reactants (weak acid or weak base)
A weak base will produce a ______ conjugate base
strong
Name 7 strong acids
H2SO4
Name 7 strong bases
O2-
Is ammonia a strong base?
Nope!
Is water amphoteric?
Yes
Do pure liquids and pure solids go into the equilibrium equations?
Nope
Kw = ? = ? = ?
Ka x Kb = [H30+][OH-] = 1 x10^-14
Ka and pKa are ______ proportional
Inversely
pKa + pKb = ?
14
pH + pOH = ?
14
pH of a strong acid = ?
pH = -log[SA]
When doing pH and “solving for logs” what is the only value to look for?
The exponent!! This is roughly equal to the pH! e.g. pH = -log(2.5 x10^-2) …so pH = - (-2)
pH of a weak acid = ?
pH = -1/2log(Ka[WA])
Can you ignore diprotic acids for weak acids?
Yes
What is the Henderson-Hasselbach equation?
pH = pKa + log( [WB/WA] )
What are buffers?
Mixtures of conjugate acid/base pairs.
What is the log of 1?
0
What do buffers do/how do they work?
Shift the reaction towards reactants or products to minimize changes in pH. CANNOT eliminate change however.
What is the log of -1?
-1
If your pH is less than your pKa, most of your substance will be ________.
protonated
Neutralization reactions are always _____thermic.
Exothermic
What are the 2 most typical products of a neutralization reaction?
Salt and water
What is the clue that your titration curve is strong acid + strong base (or vice versa)?
The equivalence point is exactly 7.0 because the reaction yields pure water.
A weak acid titration will yield an equivalence point of what?
Greater than 7 (a strong conjugate base)
What is true at the half equivalence point?
pH = pKa
A weak base titration will yield an equivalence point of what?
Less than 7 (a strong conjugate acid)
In terms of anions, are Cl-, Br-, or I- ever basic?
No
In terms of cations, are group I and II cations ever acidic?
No
How do you choose an indicator?
You want to choose an indicator with a pKin within 1 unit of your pKa.
