Ch 3 - Acids and Bases Flashcards
ionic reaction
a reaction in which ions participate as reactants, intermediates, or products
bronsted-lowry acids and bases
based on the transfer of a proton(H+)
- the acid is the proton donor - the base is the proton acceptor
conjugate base
what is left of an acid after it has been deprotonated
conjugate acid
the base after it has been protonated
water can function as an
acid or base
unlike resonance curved arrows these curved arrows actually represent a physical change
there is a flow of electron density that causes protons to be transferred from one reagent to another
reaction mechanism
show the reaction occurs in terms of the motion of electrons
the mechanism of proton transfer reaction involves
electrons from a base deprotonating an acid
2 ways to predict proton transfer reaction will occur
- quantitative(compare pKa values)
- qualitative(analyze the structure)
equilibrium(Keq)
the rate of the forward reaction is equivalent to the rate of the reverse reaction
pKa =
-log(Ka)
a strong acid will have a low pKa value while a weak acid will have a high pKa value
10 is more acidic than 16
pKa are in orders of magnitude
10 is six orders more than 16
the stronger acid always generates
the weaker base
the equilibrium will always favor formation of the
weaker acid(higher pKa)
if the conjugate base is stable(weak base) then
HA must be a strong acid
if the conjugate base is unstable(strong base) then
HA must be a weak acid
by determining the more stable conjugate bases we can determine
the stronger acid
4 factors to determine negative charge stability
- which atom bears the charge
- resonance
- induction
- orbitals
Which atoms bears the charge with acidity
- deprotonate each of the compounds and draw the conjugate bases
- if same row the more electronegative CB will be more stable and thus a stronger acid
- if same column then the larger one will be more stable and a stronger acid
Resonance and Acidity
- if there is resonance(delocalized electrons = more stability = more acidic) then they will be more acidic than localized pairs
- carboxylic acids
- the acidity of carboxylic acids highlights that acidity is relative
Induction and acidity
- as induction increase the negative charge is spread out over the molecule creating more stability and leading to a strong acid
Orbitals and acidity
sp>sp2>sp3 has greater acidity
In general the four factors for acidity rank:
- Atom charge>resonance>induction>orbital
o ARIO
leveling effect
bases stronger than OH^- can not be used in a water solvent
- the base will be destroyed by the solvent and replaced with a hydroxide ion - a different must be used which also has its own leveling effect limit
different solvents must be used for working
with very strong bases
sterically hindered
an ion which is very bulky and less capable of interacting with the solvent is less stable
- this solvent effect is generally weaker than any of the ARIO items - less efficient at forming stabilizing solvent interactions
counterions
positively charged species which always accompany a negatively charged base
OH- is actually something like NaOH, LiOH, KOH even if
the counterion is not written
the counterion typically has
little to no role in reactions
lewis acids and bases focus on
electron transfer instead of protons(bronsted lowry definition)
lewis acid
electron acceptor
lewis base
electron donor
Bronsted-Lowry Acid
proton donor
Bronsted-Lowry Base
proton acceptor
Bronsted-Lowry acid-base reaction produces
a conjugate acid and conjugate base
Reaction mechanism
shown by curved arrows
the mechanism of proton transfer always involves
at least two curved arrows
for an acid-base reaction occurring in water the position of equilibrium is described using
Ka rather than Keq
typical pKa values range from
-10 to 50
A strong acid has a _____ pKa while a weak acid has a ______pKa.
low
high
Equilibrium always favors formation of the _______acid
weaker
higher pKa
if A^- is stable then
HA is a strong acid
if A^- is unstable then
HA must be a weak acid
to compare HA and HB compare the _____.
stability of the conjugate bases
stability of the conjugate bases to determine stability of the acid
4 factors:
- Which atom bears the charge
- resonance
- induction
- Orbitals
ARIO
ARIO
Atom, resonance, induction, and orbitals
when multiple factors compete for strength of an Acid this order is priority
stability of the conjugate bases to determine stability of the acid
4 factors:
1) Which atom bears the charge
same row then the higher electronegativity bears charge
same column then the larger size bears the charge
stability of the conjugate bases to determine stability of the acid
4 factors:
4) Orbitals
sp>sp2>sp3
sp(striple bond) will be closer to the nucleus and more stable producing the strongest acid
stability of the conjugate bases to determine stability of the acid
4 factors:
2) resonance
delocalized electrons will stabilize the structure creating a stronger acid
stability of the conjugate bases to determine stability of the acid
4 factors:
3) induction
electron withdrawing groups, such as halogens stabilize a nearby negative charge leading to stronger acids
the equilibrium of an acid-base reaction always favors the
more stabilized negative charge
sterically hindered solvents are generally less
efficient at forming stabilizing solvent interactions
