Acids And PH Flashcards
Acid
Proton donor
Base
Proton acceptor
Alkali
Base that’s soluble in water
Acid base general equation
HA + B —> BH+ + A-
A + B —> CA + CB
Conjugate base
Base derived from acid
Conjugate acid
Acid derived from a base
Strong acid definition and example
Ions fully dissociated in water
HCl —> Cl- + H+
Weak acid definition and example
Ions slightly dissociated in water
CH3CO2H —>< H+ + CH3CO2
constant k indicates dissociation level
Mono/di/tri basic acid examples and dissociation trend
Mono hydrochloric HCl
Di sulphuric H2SO4
Tri phosphoric H3PO4
1st dissociation strongest
3rd dissociation weakest
pH definitions and equation
H+ conc
pH = -log[H+]
[H+] = 10^-pH
Strong Vs weak acid trends in pH and [H+]
Strong, +pH 1, xconc 10
Weak, +pH 1, xconc 20
Mono/di/tri strength compared to [acid]
Mono =
Di >/=
Tri >
Kw equation and alkaline solutions
Kw = [H+] x [OH-] = 1x10^-14
298K, pure water
[H+] = Kw/[OH-]
Strong acid and alkali calculations
Mol H+/OH- before mixing
Find excess conc
Moles/new total vol
Kw, find new H+
Use pH equ
Amphoteric
Accept/donate protons simultaneously
Ka expression and simplification
([H+][A-])/[HA]
[H+]^2/[acid]
Ka assumptions and their effect
Acid provides more H= than water, ignore water H+, [H+] = [A-], overestimate top
Fails when [H+] is very small/close to Kw
Little dissociation, most acid is HA, [acid] = [HA], overestimate bottom
Fails when [H+] is very large/close to 1
Titration curve marking points
Ph vs acid/alkali volume
Start pH
Flattish start
Vertical/equivalence volume
Vertical length
Final pH (never reaches 14, initial acid dilutes)
Describe the different titration curves
SS steep, steep
SW steep, gentle
WS gentle, steep, initial rapid
WW gentle, gentle, initial rapid
Di/tri protein, multiple equivalence/midpoints
Calculating Ka from a titration curve
Half equ point
A- = HA
A-/HA = 1
Ka = [H+]
(-log = p)
PKa = pH
Indicator compositions and equation
Weak acid and cb that are different colours
Changes colour at equivalence point
PKin = mid pH range
Hin —>< in- + H+
PKin = constant
Kin = ([in-][H+])/[Hin]
Methyl orange range and exclusion
3.7
Weak acid
Phenolphthalein range and exclusion
9.3
Weak base
Buffer composition ad function
Resist pH change in industrial/biochemical systems
Still changes pH a bit
Weak acid + cb
Buffer equation
[A-] /= [H+]
(More A- added)
[HA] = [acid]
(Little HA dissociation)
[A-] = [base]
(A- from cb > A- from HA)
Ph = pKa + log [base]/[acid]
Buffer equation considerations
Ratio matters not actual values
Concs after mixing
Concs before mixing get diluted
B > a, +, pH > pKa
A > b, -, pKa > pH
Buffer relative amounts
HA —>< H+ + A-
Lots, Little, lots
Add acid to buffer
Added H+ and buffer A- —> HA
More HA
Less A-
Small ratio change, large initial values
Decrease ration, increase [H+] slightly
Add alkali to buffer
Added A- and buffer HA —> H2O + A-
More A-
Less HA
Small ratio change, large initial values
Increase ration, decrease [H+] slightly