Chem 1721
Acids
strong acids:
weak acids:
Bases
strong bases:
weak bases:
`
Acid and Bases – a quick recap
HA (aq) + H2O (l) ÷ A– (aq) + H3O+ (aq)
Ka; pKa = –log Ka
HCl, HBr, HI, HNO3, HClO4, H2SO4
equilibrium in aqueous solution
H2O and A– bases compete for H+; A– stronger base than H2O
Ka related to acid strength
larger Ka (smaller pKa) . . . stronger acid
equilibrium position farther to the right
at equilibrium [H3O+] and [A–] are greater, [HA] is less
greater % dissociation
2 acids, same [ ]
lower pH (because higher [H3O+])
* for the same acid at 2 different [ ]’s, lower [ ] has greater % dissociation *
B (aq) + H2O (l) ÷ BH+ (aq) + OH– (aq)
Kb; pKb = –log Kb
LiOH, NaOH, KOH, CsOH, RbOH, Mg(OH)2, Ca(OH)2, Sr(OH)2, Ba(OH)2
organic compounds containing N
equilibrium in aqueous solution
H2O and BH+ acids compete to donate H+; BH+ stronger acid than H2O
Kb related to base strength
larger Kb (smaller pKb) . . . stronger base
equilibrium position farther to the right
at equilibrium [OH–] and [BH+] are greater, [B] is less
greater % dissociation
2 acids, same [ ]
higher pH (because higher [OH–] means lower [H3O+])
* for the same base at 2 different [ ]’s, lower [ ] has greater % dissociation *
Polyprotic Acids
H2A (aq) + H2O (l) ÷ HA– (aq) + H3O+ (aq)
HA– (aq) + H2O (l) ÷ A2– (aq) + H3O+ (aq)
dissociate in step-wise manner, i.e. one H+ donated per step
each dissociation step has a dissociation equilibrium and a Ka value
Ka1 > Ka2
H2A stronger acid than HA–
Salts
You must consider the individual IONS present in solution when the compound dissolves
cations
can be neutral or acidic
neutral if conjugate acid of strong base; Li+, Na+, K+, Cs+, Rb+, Ca2+, Sr2+, Ba2+
acidic if conjugate acid of weak base OR metal ion with high positive charge density
anions
acid
HF
HCO2H
HClO
HClO4
HOC6H5
H3PO4
H2SO4
HSO4–
base
NH3
C6H5NH2
HONH2
CH3NH2
Ca(OH)2
LiOH
Ka1; pKa1 = –logKa1
Ka2; pKa2 = –logKa2
can be neutral or basic (on rare occasions acidic)
neutral if conjugate base of strong monoprotic acid; Cl–, Br–, I–, NO3–, ClO4–
basic if conjugate base of weak acid
acidic only if the conjugate base of a polyprotic acid and has an acidic H (i.e. HPO42–)
strong or weak?
conjugate base
neutral or weak base?
ionization equation
strong or weak?
conjugate acid
neutral or weak acid?
ionization equation