Acid/Base Chem

Question 1

Bronsted-lowery definitions

Answer 1

acids = proton donors
bases = proton acceptors

Question 2

Lewis definitions

Answer 2

acids = accept a share in electron density (electrophiles)
bases = donate a share in electron density (nucleophiles)

** use this definition when thinking about solving acid-base questions

Question 3

Conjugate acid/base pairs

Answer 3

to get to conjugate acid: add a proton, lose a lone pair

to get to conjugate base: remove a proton, add a lone pair

Question 4

Ka

Answer 4

• the equilibrium constant for a given acid base rxn; describes the extent to which products/reactants are favored over the other
• large Ka = product favored
• small Ka = reactant favored

Question 5

pKa

Answer 5

• value that helps decide acid strength
• large pka = lower acid strength (more stable acid)
• small pKa = greater acid strength (less stable acid)

Question 6

To compare base strength, look at the conjugate acid species’ pKa values and make a statement about their strength and then ___ it to see what it means for the base strength

Answer 6

flip it ; strong acid = weak base and vice versa

Question 7

Stable vs Unstable

Answer 7

• • stable = weak
• stable acids are weak acids
• stable bases are weak bases
• • unstable = strong
• strong acids are unstable
• strong bases are unstable

Question 8

Arrow drawing

Answer 8

• draw arrow from the basic atom (nucleophile) to the proton (electrophilic atom) - density flow from high to low

Question 9

Thinking about product/reactant favored

Answer 9

• the direction of the equilibrium will always favor the side with the higher pKa acid (less strong aka MORE stable)

Question 10

equilibrium

Answer 10

the steady state for a given reaction where the opposing reactions are balanced energetically to favor the highest concentration of the most stable acid-base pairs

Question 11

Electronegativity

Answer 11

• higher EN atoms will have weaker acidic-hydrogen bonds and will be better able to accommodate an extra lone pair when deprotonated to form the conjugate base species
• EN will differentiate two acids’ acidity when the two atoms are located in the same periodic row
• so acidity will increase as the stability of the conjugate base increases

Question 12

Size (atomic radius)

Answer 12

• larger atoms have weaker acidic-hydrogen bonds and will be more apt to stabilize a negative charge in the conjugate base (due to greater charge dispersion)
• size will differentiate two acids acidity when the two atoms are located in the same periodic column
• acidity increases as the conjugate bases’ stability increases

Question 13

Hybridization State (orbital)

Answer 13

• hybridized atoms with greater s character will be effectively higher in EN than hybridized atoms with less s character
• hybridization will differentiate comparable atoms that differ in the hybrid orbitals used to bond to the acidic hydrogen
• acidity increases with the conjugate base stability therefore sp hybridized is more acidic than sp2 which is more acidic than sp3 (bc sp hybridized is more STABLE and is the base)

Question 14

Inductive electron donation

Answer 14

• inductive electron donation acts to stabilize the acid form and destabilize the conjugate base
• inductive electron withdrawal net decreases acidity; the closer the inductive atom/group is to the acidic proton, the weaker the acid strength
• alkyl groups (R groups) are electron donating/releasing and therefore when attached weakens acid strength because it stabilizes it

Question 15

inductive electron withdrawal

Answer 15

• inductive electron withdrawal acts to destabilize the acid form and stabilize the conjugate base
• inductive electron withdrawal net increases acidity; the stronger the inductive atom/group, the greater the acid strength; the closer the inductive atom/group is to the acidic proton, the greater the acid strength
• increasing acidity = increasing conjugate base stability
• halogens are electron withdrawing

Question 16

resonance

Answer 16

• the ability to delocalize electron density in the conjugate base affords more stability to the base compared to the stability of a base that has an isolate, non-delocalizable charge
• resonating a negative charge away from the point of origin will stabilize the base, therefore increasing the acidity of the conjugate acid species
• increasing conjugate base stability = increasing conjugate acidity