Exam 2 Flashcards
Aqueous solution: solvent = ?
water = solvent
Dissociation
species break apart;
A –> B + C
Ionization
dissociation into 2 ionic species;
A –> B- + C+
M =
mol/L
Cm^3 =
mL
Equilibrium constant for dissociation in water @ 25°C (Kw) =
1.0 x 10^(-14)
[H+] > 1 x 10^(-7) M =
acidic!
(implies [OH-] < 1 x 10^(-7) M)
[H+] < 1 x 10^(-7) M =
basic!
(implies [OH-] > 1 x 10^(-7) M)
[H+] = 1 x 10^(-7) M =
neutral!
(implies [OH-] = 1 x 10^(-7) M)
pH
calculated w/ equilibrium concentration of H+ and OH-
↑ acidity = ____ pH
↓ pH
↑ basic = _____pOH
↓pOH
↑ pH = _____ pOH
↓ pOH (inverse)
pOH + pH =
14 (at 298 K)
pH < 7 =
acidic
pH = 7
neutral
pH > 7
basic
strong acids (list):
HCl, HBr, HI, HNO3, HClO4, H2SO4
strong bases (list):
Group 1: LiOH, NaOH, KOH
Group 2: Ca(OH)2, Sr(OH)2, Ba(OH)2
Strong acids (SA):
- completely ionize in water
- Release 1 mol H+ / 1 mole of strong acid in water
Group 1A (alkali metals) strong bases:
Release 1 mol OH- / 1 mol strong base in water
Group 2A (alkaline earth metals) strong bases:
Release 2 mol OH- / 1 mol strong base in water
Weak acid:
partially dissociate in water
- Holds onto proton
- Smaller dissociation constants
Ka =
(products) / (reactants)
Cations behave like ___ ____ except strong bases (Li+, Na+, Ca2+, Sr2+, Ba2+)
weak acids
Weaker acid =
↓ Ka = ↑ pKa
Stronger acid =
↑ Ka = ↓ pKa
the acid dissociation constant of a weak acid will be…
much smaller than 1
Calculating H+ concentration due to a weak acid will invariably involve _____ ______
equilibrium tables!
cation
positively charged ion
anion
negatively charged ion
M =
mol/L (molarity)
x =
extent of hydroxide ionization
WGJ equation: x =
x = [OH-] = sqrt (KbMb) = (KbMb)^(1/2)
Weaker acid =
↓ Ka = ↑ pKa
Stronger acid =
↑ Ka = ↓ pKa
Weaker base =
↓ Kb = ↑ pKb
Stronger base =
↑ Kb = ↓ pKb
how basic are hydroxides?
the strongest bases!
Bronsted Lowry model
- acid = proton donor
- base = proton acceptor
Acid/base reaction = (another name)
proton transfer reaction
Bronsted Lowry: Conjugate acid
formed when a proton (hydrogen ion) is added to a base
- H+ donor! (reactant)
Bronsted Lowry: Conjugate base
formed when a proton (hydrogen ion) is removed from an acid
- loses an H+ (b/w reactants–>products)
In the forward direction,
CA = H+ donor (reactant)
CB = lost an H+ (product)
In the reverse direction,
CA = H+ donor (product)
CB = lost an H+ (reactant)
Monoprotic acid
containing 1 ionizable proton (H+)
Diprotic acid
containing 2 ionizable protons (H+)
Polyprotic acid
containing multiple ionizable protons (H+)
Sulfuric acid
strong acid w/ 2 H+ to give
Second H+ is…
harder to remove than first
- Ka2 < Ka1
Conjugate Acid
proton donor (loses an H+ b/w reactants –> products)
Conjugate Base
compound w/ 1 less H+ (product)
- usually (-)
if conjugate acid is strong, conjugate base is usually…
weak
if conjugate bas is strong, conjugate acid is usually…
weak
many anions (-) behave as __ in water…
weak base
many cations (+) behave as ___ in water…
weak acids
titration
driven acid/base reaction
- @ least 1 is strong: SA/SB, SA/WB, SB/WA
buffer system
A/B/water solution (Acid + Base + Water)
- contains comparable amounts of conjugates (ex: 1:10 or 10:1 or 3:5 –> close)
- moL A/ moL B / in water where moL A ≈ moL B
Ka (cation) > Kb (anion) =
acidic
Ka (cation) < Kb (anion) =
basic
pKa (cation) > pKb (anion) =
acidic
pKa (cation) > pKb (anion) =
basic
A buffer is resistant to pH change from addition of a …
SMALL amount of strong acid or of strong base
the buffer buffets the over-production of either __ or ___ . Thus, a buffer is resistant to __ or ___ change.
H+ or OH-ion
- to pH or pOH change
if the strong species is the limiting reactant….
you will have a buffer at the end of the reaction
if you use mols, you must use ___ for volume
Liters
if you use mL for volume, you must use
mm. mol
For conjugates, pKb + pKa =
14
steps to identify if a solution is a buffer after a reaction?
- cross out spectator ions
- if both are weak; do you have HB/B-? = buffer!
- if not (SA/WB, SB/WA, or SA/SB): - if SA/SB: no buffer (unless Mol SA = Mol SB)
- if SA/WB or WB/SA: write net ionic (mol ~= mol?)
Can you demonstrate how HClO2 behaves as a weak acid in water?
HClO2 (aq) –>/<– H+ (aq) + ClO2 ̄ (aq)
When can the protons, H+, released by the water reaction be ignored compared to the protons
released by a weak acid in water?
protons released by water dissociation can be ignored compared to those
released by a WA in water when…
sqrt(KwMw) =7.5 «_space;sqrt(KaM)
define buffer
an aqueous system containing comparable amounts of a weak acid, HB, and its conjugate weak base B ̄ —perhaps after a reaction!!!
limiting reactant is…
the reactant that results in the least amount of product if all other reactants were in excess
when a strong acid (SA) is added to an (aq) solution w/ a weak base (WB) a ___ will occur
titration
if the weak species = limiting reactant, there will be ____ after the reaction.
NO BUFFER
you can replace strong acids w/ ____ in the reaction b/w SA/SB
H+ (aq)
- H+ + OH- –> H2O
you can replace strong bases w/ ____ in the reaction b/w SA/SB
OH- (aq)
- H+ + OH- –> H2O
you can replace strong acids w/ ____ in the reaction b/w SA/WB
H3O+
- H3O+ + B- –> HB + OH-
you can replace weak bases w/ ____ in the reaction b/w SA/WB
B-
- H3O+ + B- –> HB + OH-
you can replace strong bases w/ ____ in the reaction b/w SB/WA
OH-
- OH- + HB –> B- + H2O
you can replace weak acids w/ ___ in the reaction b/w SB/WA
HB
- OH- + HB –> B- + H2O
INDICATORS are subtances added…
in a few drops to a solution
- the solution is titrated and the indicator changes color as a function of the solution pH
-they are weak acids (Hin) that change color according as HIn or In- is the predominant species in the solution to be examined
The indicator solution changes color when
[In-] ~ [HIn]; the precise condition [In-] = [HIn] is called the endpoint of the titration (when color changes)
at the endpoint of the titration, ______ relationship exists
[H+] = Ka –> pKa = pH
titrating a SA/WB, the equivalence point will occur at ___
pH < 7
titrating a SA/SB, the equivalence point will occur at ____
pH = 7
titrating a WA/SB, the equivalence point will occur at ___
pH > 7
at equivalence point, the mmMoL product =
mmMoL reactant
in a buffer regime:
as long as added OH- < 25 mmMoL, you will have a buffer regime (region)
titration curve: stronger acid =
more narrow curve (more vertical)
A/B/N: anion (-)
basic
- neutral if part of SA/SB
A/B/N: cation (+)
acidic
- neutral if part SA/SB
A/B/N: neutral if…
part of SA/SB (memorized list!)
Bronsted Lowry: pKb + pKa =
14
if given Ka1 and Ka2, use ___ for x = sqrt(M*K)
ONLY the larger Ka
equivalence point
point in titration at which the amount of titrant added is just enough to completely neutralize the analyte solution
- strong species = 100%
