Ch. 10: Acids and Bases Flashcards
how does an Arrhenius acid behave
Arrhenius acids dissociate to form an excess of H+ in solution
how does an Arrhenius base behave
Arrhenius base dissociate to form an excess of OH- in solution
how does a Bronsted-Lowry acid behave
Bronsted-Lowry acids are PROTON (H+) donors
how does a Bronsted-Lowry base behave
Bronsted-Lowry bases are PROTON (H+) acceptors
how does a Lewis acid behave
Lewis acids are ELECTRON pair acceptors
how does a Lewis base behave
Lewis bases are ELECTRON pair donors
what is an amphoteric species? how does it behave?
reacts like…
- an acid in a basic environment (donating proton, accepting electron)
- a base in an acidic environment (acceptation proton, donating electron)
WATER
how is water an amphoteric species
acts like an acid (donates proton) in a base
H2O + B- HB + OH-
acts like a base (accepts proton) in an acid
HA + H2O A- + H3O+
what is an amphiprotic species
species that can either gain or lose a proton
what occurs during autoionizations
amphoteric species react with themselves to yield basic AND acidic ions
H2O + H2O -OH + H3O+
what is the water dissociation constant, Kw
Kw = [H3O+][OH-] = 10^-14 at 25C (298K)
when autoionizied, the concentrations of H3O+ and OH- will always equal 10^-14 at 25C
what properties is Kw dependent on
like all equilibrium constants, Kw is dependent only on temperature. Changes to concentration, pressure, and volume will not effect Kw
what do pH and pOH scales measure
the concentrations of H+ and -OH ions in concentration on a negative logarithmic scale
what is the equation for the pH of a solution
pH = - log[H+] = log 1/[H+]
what is the equation for the pOH of a solution
pOH = -log[-OH] = log 1/[-OH]
what does pH + pOH =
pH + pOH = 14
as pH increases, pOH decreases by the same amount and vice versa
what is the approximate pvalue for n * 10^-m
p value ~ m - 0.n
ex: Ka = 1.8 * 10^-5 … pKa ~ 5 - 0.18 ~ 4.82
how are strong acids and bases different than weak acids and bases
strong acids/bases completely dissociate into their component ions in aqueous sol’ns
weak acid/bases partially dissociate into their component ions
what does log 1 =
log 1 = 0
what does log 10 =
log 10 = 1
what is the equation for an acid dissociation constant, Ka
HA + H2O H3O+ + A-
Ka = [H3O+][A-] / [HA]
WATER IS PURE LIQUID, NOT INCLUDED
what is the equation for a base dissociation constant, Kb
BOH B+ + -OH
Kb = [B+][OH-]/[BOH]
WATER IS PURE LIQUID, NOT INCLUDED
what do Kb and Ka values less than one indicate
weak bases and acids
what kind of acid-base reaction occurs in conjugate pairs
bronsted-lowry acid-base reaction
base + conjugate acid
acid + conjugate base
what is a conjugate acid
acid formed when a BL base accepts a proton
what is a conjugate base
base formed when a BL acid donates a proton
equation for dissociation constants of conjugate pairs
Ka, acid * Kb, conjugate base = Kw = 10^-14
Kb, base * Ka, conjugate acid = Kw = 10^-14
how are Ka and Kb values related
inversely
when one value is high, the other value is low
how do electronegative elements affect acid strength
- increases acidity*
- electronegative substituents positioned near an acidic proton pull electron density out of the acidic bond
- facilitates dissociation of the acidic hydrogen
what occurs during a neutralization reaction
an acid and a base are reacted together to form a salt and water
HA + BOH BA + H2O
what occurs during a hydrolysis reaction
water and a salt are reacted together to form an acid and a base
what is an acid equivalent equal to
one mole of H+ ions (H3O+)
what is a base equivalent equal to
one mole of OH- ions
what does it mean to be polyvalent/polyprotic
each mole of acid or base liberates more than one acid or base equivalent
what is the purpose of titration
to determine the concentration of a known reaction in a solution
how are titrations performed [big picture]
small volumes of a solution with known concentration [titrant] are added to a known volume of a solution with unknown concentration [titrand] until the complete of the reaction is achieved at an equivalence point
when is the equivalence point reached in acid base titration
when the number of acidic equivalents present in the original solution equals the number of base equivalents added (or vice versa)
what equation relates normalities with volumes for titrations
NaNb = VaVb
where N is normality (equivalents added) and V is volume of the solutions
what are indicators
weak acids or bases that have different colors in their protonate and deprotonated states
binding/release of a proton –> change in absorption spectrum –> perceived change in color
what occurs at the endpoint
the indicator changes to its final color
what makes a particular indicator a good choice for a titration
- weak acid/base
- Kb or Ka is lower than what is being titrated
where is the equivalence point for a strong acid/strong base titration
pH = 7
where is the equivalence point for a weak acid/strong base titration
pH > 7
reaction between weak acid a strong base produces weak conjugate base and VERY weak conjugate acid –> greater concentration of [-OH] at equilibrium
where is the equivalence point for a strong acid/weak base titation
pH < 7
rxn between strong acid and weak base produces weak conjugate acid and VERY weak conjugate base –> greater concentration of [H+] at equilibrium
where is the equivalence point of a weak acid/weak base titration
near neutral pH
both species will partially dissociate
what is a half equivalence point
point on a titration curve where half of a given species has been protonated/deprotonated
what is a buffer solution made of
a weak acid/base and its salt
ex: acetic acid (CH3COOH) and sodium acetate (Ch3COO-Na+)
ammonia (NH3) and ammonium chloride (NH4+Cl-)
what is useful about a buffer
resist changes in pH when small amounts of acid/base are added to the solution and can neutralize additions of charged compounds
equation for pH of a weak acid buffer solution
pH = pKa + log [A-] / [HA]
equation for pOH of a weak base buffer solution
pOH = pKb + log [B+] / [BOH]
what is the pH or pOH when [acid/base] = [conjugate]
log [1] = 0 so…
- pH = pKa
- pOH= pKb
what is the buffering capacity and how does it change?
it is the ability to which the buffer system can resist changes in pH
increase with higher concentration ratios of acid/base to conjugate and decreased with lower concentrations
