Upload
nananajep
View
228
Download
0
Embed Size (px)
Citation preview
7/28/2019 Review of Basic Concepts in Analytical Chemistry
1/22
Review of Basic Concepts inAnalytical Chemistry
Percent Concentrations
7/28/2019 Review of Basic Concepts in Analytical Chemistry
2/22
Weight percent, (w/w)= mass solute x 100%
mass solution
temperature invariant
same units for numerator and denominator
Volume percent, (v/v)
= volume solute x 100%
volume solution
same units for numerator and denominator
7/28/2019 Review of Basic Concepts in Analytical Chemistry
3/22
Weight/volume percent, (w/v)
= mass solute, g x 100%
volume solution, mL
Note:
units have to be specified
7/28/2019 Review of Basic Concepts in Analytical Chemistry
4/22
parts per million for dilute solutions= mass solute x 106
mass solution
= mg/L
parts per billion
= mass solute x 109
mass solution
= g/mL
7/28/2019 Review of Basic Concepts in Analytical Chemistry
5/22
Example: 4 -21 Skoog, 8th ed.
a. C KCl.MgCl2 = 1.037 x 10-2 M
b. [Mg2+] = 1.037 x 10-2 M
c. [Cl-] = 3.11 x 10-2 M
d. %w/v of KClMgCl26H2O = 0.288 % (w/v)
e. mmol Cl-
= 0.778 mmolf. ppm K+ = 405 ppm
g. pMg = 1.984
h. pCl = 1.507
7/28/2019 Review of Basic Concepts in Analytical Chemistry
6/22
Review of Basic Concepts inAnalytical Chemistry
Ionic Equilibria Calculations
]
7/28/2019 Review of Basic Concepts in Analytical Chemistry
7/22
Activity,a
x
effective concentration
arises from transient electrostaticinteractions between ions in solution
attraction between unlike charges brings ions
closer together and behave as neutralmolecules
Important in equilibrium calculations
explains behavior of strong electrolytes
7/28/2019 Review of Basic Concepts in Analytical Chemistry
8/22
Relationship between activity and
concentration
ax = x[x]
where
x = activity coefficient[x] = concentration
7/28/2019 Review of Basic Concepts in Analytical Chemistry
9/22
Activity coefficient
depends on concentration of all ionsin solution
x unity as [x] zero since theprobability of interactions decreaseswith decreasing concentration of ions
7/28/2019 Review of Basic Concepts in Analytical Chemistry
10/22
Properties of Activity Coefficients
explains non-ideal behavior of electrolytes
1. Ionic strength is minimal in very dilute
solutions
(x 1)
x decreases with increasing ionicstrength
at moderate ionic strength: x< 1
at infinite dilution, x 1, ax [x]
7/28/2019 Review of Basic Concepts in Analytical Chemistry
11/22
Properties of Activity Coefficients
2. Ionic strength determines the value of xNOT the nature of the electrolyte
3. x
is dependent on the magnitude of the
electrical charge on the ion, NOT on thesign of the charge. The higher the charge
of an ion, the farter x is from unity.
7/28/2019 Review of Basic Concepts in Analytical Chemistry
12/22
Properties of Activity Coefficients
4. The size of the hydrated ions affects xSmaller ions show greater departure for
ideal behavior vs. larger ions at the sameionic strength.
5. Ions have less effect on the activity of
neutral molecules than upon anotherelectrolyte.
6. x describes behavior of ion x in all equilibriain which it participates
7/28/2019 Review of Basic Concepts in Analytical Chemistry
13/22
Ionic strength,
property of a solution that depends on thetotal concentration of ions in solution, and
on the charge carried by each of these ions = [MiZi
2]
where
Mi= molar concentration of ion iZi = charge on ion I
Note: for very dilute solutions: m 0
x 1
ax Cx
7/28/2019 Review of Basic Concepts in Analytical Chemistry
14/22
Calculate the ionic strengths of the
following solutions:
1. 0.10 M NaCl
2. 0.10 M Al2(SO4)33. 0.15 M HCl + 0.15 M NiCl2
7/28/2019 Review of Basic Concepts in Analytical Chemistry
15/22
Ionic strengths:
1. 0.10 M NaCl = 0.10 M
2. 0.10 M Al2(SO4)3 = 1.50 M
3. 0.15 M HCl + 0.15 M NiCl2 = 0.60 M
7/28/2019 Review of Basic Concepts in Analytical Chemistry
16/22
Debye-Hckel Equation-log x = 0.51Zx
2
1 + 3.3 ax
where it the effective diameter of hydrated ion x innanometers, 10-9 m
Debye-Hckel Limiting Law
-log x
= 0.51Zx
2
for low ionic strength solutions ( < 0.01 M)
7/28/2019 Review of Basic Concepts in Analytical Chemistry
17/22
Calculate Fe2+using the DHL
given that = 0.75 and aFe2+ = 0.9
Ans. = 0.20
7/28/2019 Review of Basic Concepts in Analytical Chemistry
18/22
Review of Basic Concepts in
Analytical Chemistry
Chemical Equilibrium
7/28/2019 Review of Basic Concepts in Analytical Chemistry
19/22
Types of Equilibrium Constants:Thermodynamic (K)
mathematical description of equilibriumcondition
Consider the reaction
mA + nB pC + qDK = (aC)
p(aD)q
(aA
)m(aB
)n
at 25oC, depends on T, solvent
7/28/2019 Review of Basic Concepts in Analytical Chemistry
20/22
Types of Equilibrium Constants:Concentration based (K)Note that ax = x[x]
If solutes have small difference betweenactivity and equilibrium concentration
for the reactionmA + nB pC + qD
K = (caC)p(DaD)
q
(AaA)m(BaB)
n
7/28/2019 Review of Basic Concepts in Analytical Chemistry
21/22
Types of Equilibrium Constants:Concentration based (K)
K = (ca
C)p
(Da
D)q
(AaA)m(BaB)
n
K = [C]p[D]q . [c]p[D]q[A]m[]n [A]
m[B]n
K = K . [c]p[D]q
[A]m[B]
n
7/28/2019 Review of Basic Concepts in Analytical Chemistry
22/22
Types of Equilibrium Constants:
Note:
at infinite dilution, K K
most calculations use K instead of K;
molarities as approximations of activitiessince x difficult to calculate due tonumerous unknown parameters