Properties of Solutions (Acids + Bases + Buffers + titrations) Flashcards
what is the ionic product of water
1 x 10^-14
what is a bronsted-Lowry acid ?
proton (H+) donor
what is a Bronsted-Lowry Base?
proton (H+) acceptor
what does amphoteric mean ?
able to act as both an acid and a base.
what is an Arrhenius acid?
a species which increases the number of H30+ ions when dissolved in water (pH decreases)
what is a Arrhenius base?
a species which increases the number of OH- ions when dissolved in water (pH increases)
what is a lewis acid
electron pair acceptor
what is a lewis base
electron pair donor
the Arrhenius acids are limited to …
aqueous solutions
the equation for strong acid pH =
-log (c H30+/c standard)
in an acid base reaction the equilibrium favours the side with the … this is because…
weaker acid and base, because they are more stable and have lower potential energies.
how do we determine the pH of weak acids/bases
first we find the equilibrium constant - in this case known as the Ka (acid dissociation constant)
Ka of pure liquids =
1
using the Ka we can calculate the …
pKa
for weak acids the equilibrium lies far to the…
left
after finding x in the pH weak acid calculations, how do you find the pH?
pH = -logx
pKa + pKb =
pKw = 14
Ka x Kb =
Kw
what is the inductive effect?
occurs when electron-withdrawing or electron-donating groups in a molecule cause a change in electron density. this causes the pH to change.
inductive effect -
the more electronegative the bonding group the ____ the acid
stronger
inductive effect -
the _____ the bonding group the stronger the acid
closer
inductive effect -
the ____ of the bonding group the stronger the acid
more
the ___ resonance forms the ____ stable the anion and hence the stronger the acid
more, more
what makes up a buffer solution?
mix of either a weak acid or base and its corresponding salt.
what is the first step of finding buffer pH of the weak acid and strong base titration?
calculating the initial moles of the reactants
what is the second step finding buffer pH of the weak acid and strong base titration?
calculating the final moles of the weak acid and its conjugate base
final moles of the weak acid =
initial moles of weak acid - initial moles of strong base
final moles of conjugate base =
initial moles of strong base
what is the 3rd step of find the buffer pH of a weak acid and strong base titration?
using the buffer pH equation
how do you find the pKa from the Ka
pKa = -log(Ka)
what is the equivalence point?
when the same volume of the acid and base have been used in the titration
what is the halfway point
when half the volume of weak acid (in the burette) is added to the base.
what does association mean ?
the addition of two or more substances together to form a larger entity
what is the Kw of water ?
1 x 10 -14
the pKa of strong acids is a ___ number
small
the Ka of a strong acid is a _____ number
big
is ammonium an acid or a base
NH4+ is an weak acid
is ammonia an acid or a base
NH3 is a weak base
how do you calculate the initial pH of a buffer solution - titration q
same why as normal weak acid/base pH calculations - without - x on the bottom.
how do you calculate the pH of a buffer solution during the reaction - titration q (random and halfway point)
finding initials and finals.
how do you find the concentration of the conjugate base in an equivalence point q (when the volumes are equal.
since the nACID = nBASE = nCONJBASE.
this means that cCONJBASE = n/Vtotal
what should we do In the equivalence point equilibrium qs
- find the final concentration of the conj base.
- set up dissociation equilibrium reaction.
- same as weak base pH questions - you don’t need to put - x on the bottom.
what are the 3 assumption points for weak acids in a equilibrium reaction when finding the pH
- acid is a weak acid .
- eq. lies far to the left.
- assume dilute solutions.
what are the assumptions for buffer questions ?
- acid is a weak acid and doesn’t fully dissociate, assume the concentration = c.
- conj base (from main equilibrium reaction) is a weak conj base and dissociates into conj base from specific reaction and the metal ion. assume conj base from specific reaction = c of conj base from main equilibrium.
how does the inductive effect work.
a high electronegative group near the site of interest pulls the electron density towards itself (I-), this causes the site of interest to become more stable and therefore strengthen the acid.
