Acids and Bases

Question 1

acid

Answer 1

donates a proton

Question 2

H+ ion in solution

Answer 2

H+ = too reactive to exist for long in presence of water

rapid undergoes addition to a molecule of water to form the hydronium cation - H3O+

Question 3

equilibrium

Answer 3

occurs when conc. of its constituent chemical species are not changing with time

rate of forward reaction = rate of reverse reaction

Question 4

equilibrium constant

Answer 4

[Kc]

product of conc. on the RHS divided by product of conc. on LHS

Question 5

what measures the acidity of a solution?

Answer 5

pH

log of H3O+ conc.

Question 6

strong acid (Ka and pKa)

Answer 6

large Ka

low pKa

Question 7

how is the strength of a base measured?

Answer 7

basicity constant

B + H2O -> BH+ + OH-

Question 8

strong base (Ka and pKa)

Answer 8

small Ka for conjugate acid

higher pKa

Question 9

interpretation of pKa value

Answer 9

equal to pH of solution in which the weak acid is 50% dissociated

Question 10

pKa

Answer 10

property of a particular compound

refers to its intrinsic ability to dissociate a proton

Question 11

equilibrium in the reaction of an acid with a base

Answer 11

favours side with weaker acid/base combination

Question 12

substituent effects - anions

Answer 12

[inductive effect]

anions are stabilised by the electron withdrawing inductive effect of the electronegative (chlorine) ions

• > withdraw e- density
• > no longer localised only on oxygen

favour acid dissociation equilibrium

Question 13

substituent effects - methyl groups

Answer 13

anions are slightly destabilised by electron donating inductive effect of alkyl substituents

• > push e- density onto oxygen
• > disfavour dissociation

Question 14

Lewis acid

Answer 14

electron-pair acceptor

all Bronsted-Lowry acids contain a proton, but Lewis acids don’t need one

Question 15

Lewis base

Answer 15

electron-pair donor