A) pKa + pKb = 14
16.81
B) SALTS IN WATER: Change in pH
1) Look at each part:
a. Cation
i. Alkali and alkaline – do nothing b/c they used to be strong bases
ii. Used to be a weak base – lower pH – increase H+ by giving up H+
iii. Any metal ions – lower pH – shift e- density in H2O, releasing H+
b. Anion
i. Used to be a strong acid – do nothing
ii. Used to be a weak acid – increase pH – grabs H+, increases OHIf ii cation and ii anion, then whichever has a larger Keq will win
1)
2)
3)
4)
5)
6)
7)
Ba(C2H3O2)
NH4Cl
KNO3
NaNO3
KBr
BaCl2
CH3NH3Cl
C) Lewis Acid – accepts eLewis Base – donates eEx: 16.101, 16.102
D) Binary Acid Strength
H-X
The more electronegative X is, the stronger the acid
The more O you have, the stronger the acid.
CH 17 –
E) Def’n of COMMON ION EFFECT – adding some of the product to the solution will
stall the ionization of a weak electrolyte (the zeros in the ICE table are now not zeros!)
Review Buffer Calc:
1) Put in values: Weak acid concentration, acid’s “butt” concentration, H+ = 0
2) Don’t forget to balance equation before putting +x and –x in the CHANGE row
3) Set up Ka expression and plug in the EQUIL row. Fudge the small changes or do
quadratic equation.
4) X = [H+]
5) From that, get pH.
OR
Use Hendelson-Hasselbach: pH = pKa + log (base/acid)
where base = acid’s “butt”
*****BufferpH demo
F) BUFFER CAPACITY – amount of “stress” a buffer can take before it poops out and
pH goes nuts
It depends on amount of weak acid or “acid butt” that’s in there! Remember pieces of
paper in room – if you run out on one side, then buffer is done.
P 730 DIAGRAM
G) TITRATIONS
Two types:
2) strong acid – strong base
i. initial pH – pH of acid
ii. goes up, slowly
iii. shoots up around eq point b/c running out of acid
iv. pH = 7 at eq point
v. pH shoots up to pH of base being added
pH calcs – figure out how much got “taken care of”, then do the pH of what’s left. Don’t
forget that pH is of [H+] = MOLARITY, so you need TOTAL VOLUME after titration!
Before
Moles of H+
Moles of OH-
After
EX: You have 50 mL of a 0.1 M HCl. You titrate in 49.0 mL of 0.1 M NaOH. What’s the
pH? (p 733)
3) weak acid – strong base
Same thing, only you have to use Ka to get the [H+]. Before, we just subtracted to get
it. Now, get the H+ from in the Ka expression
EX: You have 50 mL of a 0.1 M HC2H3O2. You titrate in 45 mL 0.1
PRECIPITATES
SELECTIVE PPT