acid base week 2

levelling effect

all strong acids and bases are equally strong in water

strongest acid and base possible in water are

H₃O+ and OH-

at low pH/high [H₃O+], weak acids and bases are pushed towards

their protonated forms

acid-base buffer

a solution that lessens the impact of addition of acid or base on pH

buffer usually consists of

conjugate acid-base pair where both species are present in appreciable quantities in solution

buffer components HA and A- are able to

consume small amounts of added OH- or H₃O+ by shifting equilibrium position

buffer capacity

measure of the strength/ability to maintain pH (want high concentrations of each component and them to be closer to each other

buffer range

pK_a ± 1

pK_a of the weak acid should be close to

desired pH

preparing buffers

choose conjugate acid/base pair, calculate ratio of buffer component concs, determine buffer conc and volume of stock solutions, mix solution and correct pH if needed

acid-base titration

determine concentration of an acid/base with a solution of base/acid of known concentration, utilizing a visible indicator

acid-base indicator

weak organic acid whose color differs from that of its conjugate base

ratio of [Hin]/[In-] depends on

[H₃O+] i.e. changing pH makes one conc up one conc down, changing color

strong acid-strong base titration case

initial pH is low, increases gradually until base and acid are equimolar and the pH rises very rapidly at this equivalence point (pH = 7 for this case), pH afterward depends on excess of titrant and increases slowly

weak acid-strong base titration

initial pH is higher than strong-strong, increases gradually throughout buffer region(weak acid ←→conjugate base), equivalence point pH is higher than 7 due to reaction of conjugate base with H₂O