CH 7 Flashcards
Arrhenius Theory 1887
Acid: a substance that liberate (free) hydrogen ions
Base: substance that supplies hydroxyl ions on dissociation
Bronsted Lowry theory 1923
is more useful than the Arrhenius theory because it represents the ionization in both an aqueous and non-aqueous system
Acid: is a substance both charged or uncharged capable of donating a proton
Base: is a substance charger or uncharged capable if accepting a proton from an acid
strength of acids and bases
the relative tendencies of the substances to give up and take on protons
strength varies with the solvent
acid is strong= (high tendency) readily gives up protons
base is strong= readily accepts protons
acid is weak= (low tendency) readily gives up protons to SMALL extent
strength of acid
it depends on not only the ability to give up protons but also ability of solvent to accept the protons from the acid (aka: BASIC STRENGTH of solvent)
HCL
is a strong acid in water, because it readily gives up a proton
is a weak acid in glacial acetic acid
shows that strong and weak acid DEPENDS on solvent
Acetic Acid
is a weak acid in water because it gives up protons readily only to a small extent
is a strong acid in liquid ammonia
shows that strong and weak acid DEPENDS on solvent
solvent classifications
protophilic - basic solvent, accepting protons from solute (acetone, ether, liquid ammonia)
protogenic- proton donating compound (formic acid, acetic acid, sulfuric acid, liquid HCL, liquid HF)
amphiprotic- proton acceptors and proton donors (water and alcohol)
aprotic- hydrocarbons, neither accept or donate protons and is neutral, they can be useful for studying reaction free of solvent effects
cations
NH4+ and h30+
Anions
hso4- and ch3coo-
neutral
HCL and NH3
protolytic RXN
is protolysis
HCL+ H2O —> H30+ +Cl-
(acid 1)(base2)(acid 2)(base 1)
this is a IONIZATION Rxn
types of rxn
neutralization
hydrolysis
displacement
NH4+ +OH- —> h20 + NH3
neutralization
H30+ + OH- —> h20 + h20
neutralization
HCL + NH3—–> nh4+ + cl-
neutralization
h20 + ch2coo- —-> ch2cooh + oh-
hydrolysis
NH4+ + H20—->H30+ + NH3
HYDROLYSIS
acid-base rxn
acid reacts with acid to form a new acid and base (transfer of protons, so it is also called protolytic or protlysis)
h30+
hydronnuim ions, hydrated proton
displacement rxn
a special type of neutralization involves the displacement of a weaker acid such as acetic acid from its salt.
Lewis electronic theory
acid is a molecule or ions that accepts an electron pair to form a covalent bond
base is a substance provides the pair of unshared electrons by which the base coordinates with an acid
the H+ proton(acid) will attach to the unshared electron pair of N on NH3 to make NH4+
you do not need to contain hydrogen ions or hydroxyl ions to be and acid or base according to LET
acid-base equilibria
equilibrium: a balance between two opposing forces of action. it is dynamic equilibrium of the two velocities
reversible reaction (weak electrolytes)
concentration of reactants and products are constant
Ionic equilbria
bronsted lowry
irreversible
to completetion
Acid base equilbria of acetic acid
HAc + h20 -><- h30+ + Ac-
Rf
the rate/velocity/speed of the forward reaction is proportional to the concentration of the reactants
Rf= k1 x [HAc]1 x [h20]1
k= specific reaction rate
Rr
the reverse reaction of reformation of unionized acetic acid is proportional to concentration of reactants
Rr= K2 x [h30+]1 x [Ac-]1
Rf=Rr
k1 x [HAc]1 x [h20]1=K2 x [h30+]1 x [Ac-]1
k=k1/k2=product=reactants
dissociation constant
ka=55.3 k=product/HAc
summary of ionization of weak acids
uncharged weak acid (HB) in water
HB + H2O —><— H30+B-
Dissociation constant:
Ka= [h30+][b-]/ HB
[H30+] =sqrt kaC
x^2/c-x
x^2 is the value in moles of two products dissociated
x is dissociation # in moles
c is original amount in moles/liter or M
dissociation of Salt
ammonium chloride in water
Nh4+cl- —> NH4+ + Cl-
NH4+ +H20 –><— H30+ + NH3
ka= [h30+] [NH3]/[NH4+]
Summary of ionization of weak acids
charged weak acid BH+ in water
BH+ +H20–><— h30+ +B
dissociation contant [h30+][B]/ bh+
ionization of weak bases
NON-ionized weak base,B, in water
B + H20—><— OH- +BH+
KB= [OH-] [BH+]/[B]
[oh-] =sqrt KbC
dissociation of salt (base)
sodium acetate in water
Na+ CH3COO- —> Na+ +CH3COO-
dissociation:
CH3COO- + h20—> OH- + CH3COOH
Kb= [OH-][CH3COOH]/CH3COO-
summary of ionization of weak bases
anionic base (B-) in water
B- +H2O –><– OH- +HB
Dissociation constant
kb= [OH]- [HB ]/ B-
ionization of water
water
h20 + h20 —><— h30+ + OH-
dissociation constant and concentration
k= [h30+] [ OH-]/[h20]^2
kw= K x [h20]^2
kw= [h30+] [ OH-]= 1 x 10^-14 at 25 c
[h30+]= [oh-]= 1 x 10^-7
water concentration is 1 x 10^-7 meaning can be OH- and H30+
Kw or constant of water is 1 x 10^-14
if we add more acid to pure water, the increase in hydrogen ions will decrease the hydroxyl ions so that water remain constant Kw at 1 x 10-14 at 25c
ion product of water at varying temps
25C, kw= 1 x 10^-14
pKw= 14 at 25C
if you add heat to an endothermic process, the position of equilibrium moves to the right (in forward). Ka increases! Since pKa=−logKa , an increase in Ka means a decrease in pKa .
increasing the temp from 60 to 70C, the Kw or constant of water will INCREASE( increase in temp, increases the rate of the forward rxn and dissociation constant). but the pkw will decrease with increasing temp
decrease in temp= increase Pka and decrease the ka, it production of ions REDUCE
Kw will increase temp rxn and is endothermic, more product is being favored in the forward rxn at high temp
at high temp more water molecules gain enough energy to break and dissociate and this leads to increase in concentration of OH- and H+ ions
relationship between Kb and ka
dissociation constant of weak acid (uncharged) HB and H20
HB +H20= h30+ + B
Ka= [B][h30+]/[HB]
dissociation constant of anionic base, B-
B- +h20= oh- hb
kb=[oh-][hb]/[b-]
=KaKb
=[OH-][HB]/[B-]=[B][h30+]/[HB]
=[OH-][H3O+]=Kw
=Kw= KaKb
=kb=kw/ka
=ka= kw/kb
ionization of polyprotric electrolytes
monoprotic electrolytes :
acids donate a single proton
bases accept a single proton
Polyprotic electrolytes: capable of donating and accepting two or protons
-diprotic (disbasic) acid (ex. carbonic acid) ionizes in 2 stages
-triprotic acid (trisbasic) acid (ex.phospohric acid) -ionizes in 3 stages
- look at notes for phosphoric acid equations and Ka and Kb values
ampholyte
a species can function either as a acid or base, amphoteric in nature
ex. glycine hydrochloride in water
+NH3CH2COOH +H20= +NH3CH2COO- +H3O+
+NH3CH2COO- +H20= NH2CH2COO- +H30+
+NH3CH2COO- +H30+= +nh3ch2cooh +OH-
api can be a weak acid or base
+NH3CH2COO- can act as a acid or base
H2PO4- AND H2PO4 2-
ampholytes- acid or base
+NH3CH2COO-
is the amphoteric species, is called a zwitterion, it is different from the phosphoric species(amphoteric specifies) in that it carries a positive and negative charge. the whole molecule is electrically neutral
isoelectric point
is the net movement of the solute molecules in the electric field is negligible.
ph at which the zwitterion concentration is maximum
Sorensens pH scale
the common logarithm of the reciprocal of the hydrogen ion concentration, aka hydrogen ion potential.
pH= log (1/H30+)
pH=log 1-log [H30+]
pH= -log[h3o+]
value of log 1 is 0
the pH and corresponding hydrogen and hydroxyl ion concentrations
pH of 7 (NEUTRAL) the [h30+] and [oh-] are 10^-7moles/liter
at pH of 0 (highly acidic), [h30+] 10^0=1and [OH-]=10^-14 moles/liter
at a pH=14, [H30+] 10^-14, 10^0=1[OH-]
A pH of 7 is neutral. A decrease in pH below 7 shows an increase in acidity (hydrogen ions), while an increase in pH above 7 shows an increase in alkalinity (hydroxyl ions). Each pH unit represents a 10-fold change in concentration.
pk and pOH
pH + pOH= pKw
pKa +pKb= pKw
pKa
pH,
-logka
pKb
pOH,
-log[oh-]
pk
is dissociation exponent
hydrogen ion concentration of weak acid
[h30+] = sq rt KaC
hydroxyl ion concentration of weak base
[OH-]= sq rt KbC
