Video: Kohlrausch Law Video Lecture - NEET

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exam so as per caller ashram if you take
a strong look like the blue one is my
strong lift light and the green one is
my weak electrolyte this we just saw
strong little like in the KCl and weak
is like acetic acid so for a strong
electrolyte if you see here we are
increasing the illusion here we are
going in more concentrated if you go
from right to left here diluting the
whole solution that means if you see it
going from left to right when you are
diluting the lambda I am increasing
right so morer conductivity increase
slowly on dilution this dilutions is in
this problem and further at he ma
equation there is lambda m and gimme
point is nothing but its value at
infinite dilation - a c to the power 1
by 2 C is a constant C is a constant or
a is a constant and C is concentration
and the value of a depends on solvent
Ashley right for example if you see it
depends on the pair example NaCl and KCl
will have same value of a it depends
with number of ions it produces actually
okay
for example NaCl KCl will produce 2 IC C
is here - will produce 1/9 of - positive
charge and 2 ions or one negative charge
right and UCL doing the same thing
so they'll have same value of a MGS a
hole will produce one ion of +2 charge
and this ion of negative charge calcium
sulfate also will have will produce 100
plus 2 charge CA plus 2 SF of minus 2 so
this will have seen these two will have
seen well okay these two laps a value of
a this will have same LOV this a depends
on mine solvent actually all right I
mean the number of the types of cations
and anions it produced so all the
electrolytes will have same of
particular type will have same value
okay correct but we talked about the
variation of molar conductivity of a
weak electrolyte in this case that is
not a linear function you see this is
not a linear function this is a linear
function correct this is not a linear
function see it goes something like this
it's not only about okay so the
evaluation of this molar conductivity
and infinite dilution the woman you keep
diluting you want to find the value of
conductivity here molar conductivity
here that is not very certain and for
this he proposed one more law he
proposed that at infinite dilution at
infinite dilution and this is for weak
electrolytes in fact all actually this
for all at infinite dilution the cations
and anions since it is infinitely dilute
they move independently of each other
they move independently of each other in
the solution and this idea was
discovered by Colin Ross in 1875 in 1875
he thought of this idea to prove this
what he did was he measured the molar
conductivities of strong electrolytes
please note he took strong electrolytes
and since I am talking about infinite
dilution he talked he took strong
electrolytes at infinite dilution and he
did that and let's see what the result
was so we needed to research and he
found that the molar conductivity for
the pairs of salt having a common ions
approximately same at this lambda M the
difference in lambda actually the
difference in lambda m or pairs of salt
and the pace of salt should have one
common is sin a proxy for example he has
taken ki I and nai where found the
difference
he took k BR and nab R where he found a
difference he took KCl NaCl speak yeah
KCl NaCl where he found a difference he
took kno3 nano3 where he found a
difference and he found a difference of
lambda he found that but k I nai KL for
all these Atlee the value came out to be
approximately twenty three point four
Siemens centimeter square per volt
but you observed is that means if you
see here if you take remove III you get
K minus na you remove br br because I'm
subtracting great k minus n OC else here
you get K minus a no.3 energy removed we
get Kimmel's in it so with that he came
to conclude he concluded that at
infinite dilution the cations and anions
contribute independently to the moral
con conductivities please note the
conclusion here was from this experiment
was that field since everything is
happening at infinite dilution at in
finite in collusion because at infinite
dilution you can find at least find the
molar conductivity of a strong
electrical forever we collect light you
cannot find they because the Harding
dissociated so at in fine digestion my
cations and anions
contiune contribute independently to
molar conductivity of electrolyte so
that was he concluded right he took
other pair also for example one Perry
took was any beer and any CL and he took
KBR and KCl so if you see this P R now
and he found the lambda M and I'm busy
here and he gets cancelled here Kiki get
cancelled right so in both the case in
both the case the lambda came out to be
1.8 C means 80 meter square per
right so does he told that the lambda M
that is my molar conductivity can be
expressed as sum of molar conductivities
of individuals ions of a liquid because
since they are contributing
independently I can say that lambda m
can easily be say
replaced a something what some of the
molar conductivity is of individual
electrolytes and this is nothing but
call wash law of independent migration
of mine called as law of independent
migration correct that means for example
for I have let suppose NaCl at an
infinite dilution they you want to find
the limiting molar conductivity of NaCl
so that will be nothing but limiting or
locality I'll put it not here of NaCl
with nothing but limiting molar
converted to na plus plus limiting your
locality oh and they say CL minus you
just add these two look at the that
correct but for example we have CA CN to
cacl2 in that case you get to chlorine
mines so it will be ca plus plus 2 into
limiting molar conductivity of drawing
because you get two chlorine ions and
one calcium I when cacl2 dissociate so
there's a general rule Aisling me write
that general rule the general rule is
that so if I have a electrolyte that on
dissociation gives X cations and Y
anions let suppose so the limiting molar
conductivity of the whole solution will
be nothing but X into lambda of cation
plus y into molar conductivity of an eye
correct example mgcl2 it will give you
one mg plus 1 cation and 2 and I had to
chlorine so it be lambda of mg plus 2 of
lambda truly the general rule Ashley it
gives X cations and y crimes then X into
number the molar connected and because
you are getting X number of cations in a
plus y into molar conductivity of anion
because you are getting Y number of
packets and this is the molar
conductivity is the limiting molar
conductivity Ashley for cations and
anions the popular values at 298 Kelvin
or h+ this is the value 349 c means
centimeter square per mole or na plus 50
point 1 centimeter square same in
centimeter square per mole or ki plus
73.5 cement centimeter square per more
similarly for CA plus 11.11 9 cm in
centimeter square per mole
74 for OS - we have this value 1 99.1
cement centimeter square per mole
similarly for VR minus mu QC or CSC co -
we have this value it depends on the
size you see ch3 Co - is big in size
since the anion is this this ion is
bulky conductivity is less h plus is
very nimble very small in size so in
this case if you see conductivities
almost maximum here correctly all
depends on the size of the ion now let's
see the Khan washed off of the weak
electrolytes so as I've told you
scholars log or in the this independent
migration of ions this was used for weak
electrolytes and generally because were
weak electrolyte is very difficult to
find the molar conductivity at a very
high dilution because at that high
dilution the degree of this assertion is
very high right
it's a very uncertain value so the molar
conductivity and infinite dilution so
let's suppose my is almost zero
concentration almost zero so in that
case that this association of is almost
1 that is that suppose I take a weak
electrolyte right so this is I'm
diluting it and this is my molar
conductivity right so I'm at infinite
dilution this is this alpha is almost 1
because this will be let suppose see
this becomes 0 0 at t 0 0 this becomes C
alpha so C into become C into 1 minus
alpha this becomes CL fans become C ever
write this you have seen in the
equilibrium process kind of equations so
at infinite dilution C is almost 0 and
alpha is almost 1 so but at such low
concentration we have told that
conductivity of solution is very very
low and it cannot be measured accurately
so we have we came up with this Kailash
came up with this law of independent
migration we say that at any given
concentration I mean if you just add at
infinite dilution the molar conductivity
of this solution is nothing but the
molar conductivity of individuals is
correct now at any given concentration
let let's assume we are coming with a
new formula now at any given
concentration if alpha is my degree of
disassociation sorry so my alpha I can
easily approximate alpha to be the ratio
of molar conductivities at that alpha
can be this value I this better
not hurry or let's not confuse let's
make it lambda M by lambda M naught
lambda M naught is nothing but my molar
conductivity at inside infinite dilution
right where C is almost equal to zero
and this is my molar conductivity at any
time
C is equal to C some value so I am
saying this efficient is almost equal to
the molar conductivity at a given
concentration divided by molar
conductivity at infinite dilution so I
want to find this K cream contains
nothing but CL equal concentration of
ch3co minus concentration of h+ by
concentration of ch3co version this
becomes C alpha IL power C into 1 minus
l cancel becomes C alpha square 1 minus
alpha just put the value of alpha alpha
is nothing but lambda M by lambda M
naught C into lambda M by lambda M
naught by 1 minus lambda M by lambda M
naught this value will get we solve it
you get T into lambda M square by lambda
M naught lambda M naught by M this is
what you will get the value of curiosity
you can find the value of equilibrium
constant using the value of lambda M
naught n lambda that is molar
conductivity ad infinitum Asian and
molar conducting connectivity at that
point of time where you want to find the
value of K so let's see the application
of Colorado
just see first thing is that it is used
to find the value of molar conductivity
at infinite dilution for a weak
electrolytes and infinite dilution
correct example I want to find the molar
conductivity of ch3cooh and infinite
Venusian that will be nothing but the
molar conductivity of ch3co - an
infinite halation + molar conductivity
of h+ at infinite dilution these values
you can actually give me some textbook
that is the percept equation the second
application it is used to find the
dissociation constant alpha as I told
alpha is almost equal to lambda M by
lambda M not correct
second thing once I have alpha I can
easily find the occluding constant CL
ascribe ever wonderful Atlas for this
equation correct so I can find the
dissolution constant I can find the
equilibrium constant I can find the
value of murder conductivity for a weak
electrolyte at infinite dilution thank
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