Transcript 6.전해질용액(수정) - Physical Pharmacy Laboratory

SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
I.
Properties of Solutions of Electrolytes
II.
Arrhenius Theory of Electrolytic
Dissociation
III.
Theory of Strong Electrolytes
IV.
Coefficients for Expressing Colligative
Properties
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

When under a
potential of several
volts, a direct electric
current flow through
an electrolytic cell, a
chemical reaction
occurs. The process is
known as electrolysis.
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성균관대학교 물리약학연구실
음극(cathode) : 전자가 음극으로 들어가 양이온이 환원
Fe3++e
Fe2+
양극(anode) : 음이온이 전자를 내어놓아 산화
OH-
1/4O2+1/2H2O+e
•용액 중에서의 전류 : 전극으로 향하는 양이온과 음이온의 흐름
•금속도체에서 전류 : 양이온으로 고정되어 있는 결정격자를
통하여 이동하는 자유전자흐름
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성균관대학교 물리약학연구실
Transference(transport) number : 운반율
: The fraction of total current carried by the
cations or anions is known as the transport or
transference number.
양이온이나 음이온에 의해서 운반된 전류의 총전류에
대한 분율. 이온의 속도와 관계가 있으며 빨리 움직이
는 이온일수록 많은 몫의 전류를 운반
t+ = current carried by cations/total current
t- = current carried by anions/total current
t++t-=1
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성균관대학교 물리약학연구실
I : 전류세기 ampere
E : 전위차, 전압 volt
R : 저항 ohm
I=E/R 전류흐름의 속도, 즉 단위시간에 흐르는 columb으로
표시되는 전기(전하)량 Q이다.
I=Q/t (Quantity of eletric charge : 1 coulmb = 3*109esu)
Electric energy = E * Q
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

The passage of 96,500coulombs of electricity
through a conductivity cell produces a chemical
change of 1 gram equivalent weight of any
substance
F=9.648456*104
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
R= 
l
A
 : specific resistance 비저항
l : length 길이
A : cross-sectional area 단면적
C=
1
R
=
1
A
*

l
=
1

=C *
l
A
=
: conductance 전도도
1
l
*
R
A
: specific conductance 비전도도
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성균관대학교 물리약학연구실

Rx=Rs*R1/R2

 =1/ =c*l/A=1/R*l/A

l/A=K

 =K/R

 =K*C
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성균관대학교 물리약학연구실
1
 *

c=V=

V=(1000cm3/liter)/c Eq/liter
V
=1000/c (cm3/Eq)

c=V= 1000  mhos
c
cm2/Eq
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성균관대학교 물리약학연구실
Conductance of a solution of sufficient volume to
contain 1 gram equivalent of the solute when
measured in a cell in which the electrodes are
spaced 1 cm apart
1 그램당량의 용질을 함유하기에 충분한 용적의 용
액을 전극이 1 cm 떨어진 용기중에서 측정하였을
때의 전도도
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성균관대학교 물리약학연구실

전해질의 농도와는 관계없이 분자가 이온으로
해리되는 현상을 연구하기 위해서는 specific
conductance를 사용하는 것보다 equivalent
conductance를 사용하는 것이 편리

Equivalent conductance : the conductance of a
solution of sufficient volume to contain 1gram
equivalent of the solute when measured in a cell
in which the electrodes are spaced 1cm apart.
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성균관대학교 물리약학연구실
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실

Strong electrolyte가 희석되어 감에 따라 용
액의 단위용적당 이온수가 감소하므로
-> Specific conductance는 감소
-> Equivalent conductance는 꾸준히 증가
(이온간의 간섭이 줄어들기 때문에 운동성이 향
상)
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성균관대학교 물리약학연구실
•Kohlrausch c= o-bc
(강전해질 용액)
•모든 전해질의 ion은 용액이
희박해짐에 따라 독립적으로
이동시작
•o=lcº+laº (약전해질 용액)
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성균관대학교 물리약학연구실

In solutions of nonelectrolyte
Van’t Hoff :  = RTc

in solutions of electrolyte
 = iRTc
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성균관대학교 물리약학연구실
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
•Strong electrolyte : HCl, HNO3, HI, NaOH, H2SO4, KOH,
Ba(OH)2, Ca(OH)2
•Weak electrolyte : H3BO3,H2CO3, NH4OH, HgCl2, complex ion
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
1) some drugs are more active when in ionic state
2) other compounds are active when in
nonelectrolyte
3) other compounds are active when both in ions or
neutral molecules.
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성균관대학교 물리약학연구실

 = c / o : conductance ratio

i = 1+ (v-1)

 = (i -1)/(v-1)
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성균관대학교 물리약학연구실
THEORTY OF STRONG
ELECTROLYTES
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성균관대학교 물리약학연구실
a / m = m : practical activity coefficient on the
molal scale
a / c = c : practical activity coefficient on the on
the mole scale
a / x = x : rational activity coefficient on the
mole fraction scale
-> in dilute solutions the difference among three
activity coefficients may be disregarded in which
c=m < 0.01
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성균관대학교 물리약학연구실
a+ : activity of a cation
a- : activity of a anion
mean ionic activity a=[(+c+)m(-c-)n]1/(m+n)
NaCl a=(aNa+aCl- )1/2
FeCl3 a=(a Fe+3 a Cl-3 )1/4
a=[(+c+)m(-c-)n]1/(m+n)
a=(+m - n)1/(m+n) (c+mc-n)1/(m+n)
a=  (c+mc-n)1/(m+n)
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성균관대학교 물리약학연구실
mean ionic activity coefficient
: ±= (+m -n)1/(m+n)
± = + m - n
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성균관대학교 물리약학연구실
a / m = m
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성균관대학교 물리약학연구실


When a solution is made infinitely dilute, it can be
considered to consist essentially of pure solvent.
Therefore, X1 = 1, and the solvent behaves ideally in
conformity with Raoult’s law. Under this condition, the
mole fraction can be set equal to the activity of the
solvent, or a = X1 = 1
As the solution becomes more concentrated in solute
the activity of the solvent ordinarily becomes less than
the mole fraction concentration, or a = x X1
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
4. Standard State
Reference State : the
solution in which the
concentration of the
component is equal to
the activity
activity = concentration
I = activity / concentration


Standard State : state
of the component at
unit activity
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성균관대학교 물리약학연구실

Ionic strength : 모든 형태의 ion이 정전기적 힘에
어느 정도 기여하는가를 나타내는 것

 = 1/2(c1z12+c2z22+c3z32+•••+cjzj2)
= 1/2cizi2
(ci : molar concentration, zi : valence)
ex) 0.01M KCl
 =1/2(0.01*12+0.01*12)=0.01
0.01M BaSO4  =1/2(0.01*22+0.01*22)=0.04
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성균관대학교 물리약학연구실
 < 0.02
: log i = -AZi2 
 0.02<  < 0.1 : log i = -AZi2  / (1+   )
 0.1 <  < 1 : log i = -AZi2  / (1+ aiB )+c
i : activity coefficient
ai : mean effective ionic distance
aiB=  : constants related to ionic radius of the
electrolyte
A,B : constants influenced only by the nature of for
several electrolytes at 25ºC

SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
SKKU Physical Pharmacy Laboratory
성균관대학교 물리약학연구실
COEFFICIENTS FOR
EXPRESSING COLLIGATIVE
PROPERIES
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성균관대학교 물리약학연구실

Van’t Hoff equation : Tf = iKfm
in dilute solutions, m=c, L=iKf  Tf = Lc
At a concentration of drug that is isotonic with
body fluids, L=iKf is designated here as Liso
Liso 비전해질 1.86-1.9
약전해질 2.0
1가-1가 전해질 3.4
높은원자가 전해질 >3.4
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성균관대학교 물리약학연구실
Fig. 6-7. Liso values of various ionic classes
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성균관대학교 물리약학연구실
The solution becomes more dilute, i approaches v,
the number of ions into which an electrolyte
dissociates, and at infinite dilution i = v, or i / v=1.
 The ratio i / v is designated as g and is known as
the practical osmotic coefficient when expressed
on a molal basis.
 i / v=g , Tf = iKfm = gvKfm

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성균관대학교 물리약학연구실



1-osmolal solution : A solution containing 1 mole ( 1 gram
molecular weight) of a nonionizable substance in 1 kg of
water (a 1-m solution). It contains 1 osmol (Osm) or 1000
miliosmols (mOsm) of solute per kilogram of solvent.
mOsm/kg = imm (i : number of ions formed per molecule,
mm : milimolal concentration)
Osmolarity = (measured osmolality)*(solution density in
g/ml-anhydrous solute concentration in g/ml)
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성균관대학교 물리약학연구실