Equilibrium

Question 1

acid-base titrations

Answer 1

titrand and titrant are acid and base

Question 2

titrant

Answer 2

in burette

Question 3

titrand

Answer 3

in beaker

Question 4

complexometric titrations

Answer 4

metal-ligand complexation

Question 5

redox titrations

Answer 5

titrant is oxidizing or reducing agent

Question 6

precipitation titrations

Answer 6

titrant and titrand form a precipitate

Question 7

Strong acids

Answer 7

HCl
HBr
HI
H2SO4 (first dissociation)
HNO3
HClO4

Question 8

Strong bases

Answer 8

LiOH
NaOH
KOH
RbOH
CsOH
R4NOH

Question 9

Kw=KaKb

Answer 9

For conjugate weak acid/base pairs

Question 10

Higher Ka

Answer 10

Stronger acid

Question 11

Lower Ka

Answer 11

Weaker acid

Question 12

Charge balance

Answer 12

Sum of pos charges = sum of negative charges

Charge number is the coefficient for each term

Question 13

Mass balance

Answer 13

amount of atom delivered to solution = sum of amounts of species with that atom

Ex. 0.05M H3PO4 delivered to water
[H3PO4]+[H2PO4-]+[HPO43-]+[PO44-] = 0.05M

Question 14

Formal concentration

Answer 14

moles of original chemical product in solution (F)

Question 15

Systematic treatment of equilibrium problems

Answer 15

1. Write all relevant reactions
2. Write charge balance equation
3. Write the mass balance equations
4. Write K for each rxn
5. Count equations and unknowns. Should have equal # of equations and unknowns
6. Subtract mass-balance from charge-balance
7. Express in terms of H+, K’s, etc
8. Simplify if possible

Question 16

a (alpha)

Answer 16

Fraction of concentration occupied by a speciesI

Question 17

Isoelectric pH

Answer 17

Mean of pKas of AAs (with only one amine and carboxyl)

Question 18

Cations whose salts are all soluble

Answer 18

Li+, Na+, K+, NH4+

Question 19

Anions whose salts are all soluble

Answer 19

NO3-, NO2-, CLO4-, CLO3-

Question 20

Effect of pH on solubility

Answer 20

For a salt of a weak base, solubility incr as pH decr.

At low pH, acid form is favoured, pulling more into solution

Question 21

Effect of complex formation on solubility

Answer 21

Presence of complexing agent incr solubility

Question 22

Equivalence point

Answer 22

moles of titrant = moles of titrand

Question 23

Endpoint

Answer 23

Observable change that approximates equivalence point

Question 24

Eq pt pH for strong acids

Answer 24

7

Question 25

Half-eq pt for weak acids

Answer 25

pH=pKa

Question 26

H-H equation

Answer 26

pH=pKa + log([A-]/[HA])
or
pH = pKa + log([B]/[BH+])

Question 27

How to determine pH for:
a) Initial
b) 1st buffer region
c) 1st eq pt
d) 2nd buffer region
e) 2nd eq pt
f) Excess base

Assumptions?

Answer 27

a) Ka1 (write out eq expr, solve for H+)
b) HA-/H2A ratio, H-H
c) mean(Ka1,Ka2)
d) A2-/HA- ratio, H-H
e) Kb1
f) excess OH- from SB

Ka1»Ka2

Question 28

clear 1st endpoint

Answer 28

Ka1/Ka2 >= 10^4

Question 29

When does final endpoint begin to disappear?

Answer 29

pKaf = 9 or more

Question 30

Buffering range

Answer 30

pKa +-1

Question 31

Acid-base indicators

Answer 31

Weak acids.
Colour change is in buffering region (pKa+-1).
pKa(dye) must be sufficiently larger than pKa(wa) -> dye buffer region must be in acid steep region

Question 32

Gravimetric methods, pros and cons

Answer 32

Pro: very accurate
Con: time consuming (drying precipitate)

Question 33

Argentiometric titrations

Answer 33

Titrant: AgNO3
Titrand: Halide and halide-like ions (SCN-, CN-, CNO-); precipitate with Ag+
Higher Ksp with silver, bigger drop

Question 34

EDTA titrations

Answer 34

Titrant: EDTA (complexing agent)
Titrant: metal ion
*Requires basic pH buffer, so that EDTA is only in form Y4-
Auxiliary complexing agent: (eg NH3) Complexes metal cations so that hydroxide precipitates don’t form

Higher Kf with EDTA -> greater increase

xylenol orange indicator

Question 35

Concentration of Y4-

Answer 35

pH dependent,
[Y4-]=a(6)c(edta)
At pH12: a(6)=1