Soaps & Detergents Video Lecture | Chemical Technology - Chemical Engineering

hi students now this chapter is going to
be very very interesting it's going to
be a bit different you know from the
previous chapters in this chapter we are
going to learn about how soaps and
detergents clean clothes take a look at
this you know black spot on this white
t-shirt
once we wash this t-shirt with the soap
two-spot vanishes so how did the dirt
vanish
how do soaps and detergents work that's
what we are going to learn in this
chapter soaps and detergents let's
proceed now before we learn about the
action of soap and detergent we have to
first learn about the structure of so
what does soap actually consist of well
soap in general consists of the sodium
and potassium salts of long-chain
carboxylic acids what this means is that
different soaps are basically the sodium
salts of carboxylic acids or the
potassium salts of carboxylic acids take
a look at this structure of soap here as
you can see there's a long carbon carbon
chain here at the end of this carbon
chain there is a carboxylic acid group
whose hydrogen has been replaced by
sodium so basically you know soaps have
names like sodium stearate understood
so basically sodium salts of carboxylic
acid groups form soap this is the
structure of a soap molecule this is one
example of a soap molecule sodium
stearate the chemical formula of sodium
stearate is c-17s 35c ona what this
means is you know that the carboxylic
acid which has 17 carbons when you
replace the hydrogen of that carboxylic
acid with a sodium ion you get soap
sodium stearate similarly there are many
other compounds you know which can also
be part of soap but the crux is that
there should always be a sodium salt of
a carboxylic acid one interesting
property of soaps is that soaps are
basic in nature understood they are
basic you know because soap is what soap
is the salt of a carboxylic acid
we know that carboxylic acids are weak
acids and sodium salts of we
acids are basic in nature isn't it after
all salts which are formed by a strong
base and a weak acid are basic in nature
that's why slope is basic in nature so
the soap that we use will actually turn
red litmus blue that is fascinating but
that is true so this was the structure
of soap but how does soap actually act
you know and how does it clean the
clothes well every soap particle every
soap molecule consists of two ends one
end is called the hydrophilic end and
the other end is called the hydrophobic
end the hydrophilic end is the sodium
containing end the end which contains
the sodium ion you know the end which
has the c oo
any a hydrophilic end and a hydrophobic
end the hydrophilic end is the end that
contains the sodium ion the hydrophobic
end is the other end of Biscay box-like
acid you know the end which has carbon
and hydrogen now the important property
of the hydrophilic end is that it
attracts water understood so whenever
there is water this end will want to
come in contact with water
the hydrophobic end on the other hand
repels water so you know it will want to
go away from the water
the sodium end of the sodium salt of the
carboxylic acid here attracts water
while the hydrophobic end repels water
and this property this property of one
end being hydrophilic attracting water
and one in repelling water this is what
you know gives soap it's special
cleaning property another interesting
fact is that the hydrophobic end the end
of the soap molecule which repels water
actually gets attached to oil and grease
so one end of the soap gets attached to
oil in grease and one end gets attached
to water now this was the property of
the soap molecule let's actually see how
a soap molecule removes dirt when we add
soap to water what happens is that you
know all the soap molecules form a
circular aggregate like this now these
black dots here are basically sodium
ends of the salt molecule the red chains
here are carboxylic acid chains
the sodium ents are out words while the
carboxylic acid chains are inwards and
they are attracted to each other you
know because they repel water all of
them repel water and so they come close
together to stay as away from water as
possible
on the other hand the sodium ions
attract water and so they're outwards so
they come in contact with as much water
as possible so basically every soap
molecule forms this sort of circular
aggregate or circular structure when
soap is added to water so basically
these red ends here are the hydrophobic
ends they repel water and they attract
oil these black ends here which have the
sodium ion are hydrophilic ends they
attract water and that's why they're
trying to get exposed to as much water
as possible this circular structure or
this circular spherical aggregate of
soap molecules is called a missile
understood so so forms missiles when you
know it is added to water what does a
missile have a missile has different
hydrophobic ends of the soap molecules
near each other and it has this
hydrophilic ends spread wide apart in
the form of a sphere
understood so this spherical aggregate
called missile is formed when soap is
added to water now how does this
spherical aggregate help in removing
dirt when there is a dirt particle the
missile actually surrounds the dirt
particle like this so all of these red
carbon chains with the hydrophobic ends
get attracted towards the dirt the
sodium ends or the hydrophilic ends stay
away from the dirt they don't get
attracted to oil or grease they get
attracted to the water so they are in
contact with the water thus the missile
basically traps the dirt particle like
this understood so this is the first
step in the action of soap under
particles now what happens is these
missiles grab the dirt particles and
when the water flows off the dirt
particles trapped by the missiles keep
flowing off you see generally dirt
particles are insoluble in water but
what happens is these missiles
these spherical aggregates they trap the
dirt particles and they make them
soluble in water so the dirt particles
which are initially insoluble they get
dispersed in water and they get removed
by water because of the formation of
missiles understood so this is how soap
acts and removes the dirt particles I
will repeat it for you first you know
soap molecules form a missile or a
spherical aggregate around the dirt
particles they found that because the
hydrophobic ends or oil attracting ends
of the soap molecules they touch and
surround the dirt particle the
hydrophilic ends point away from the
dirt particles so basically a spherical
aggregate is formed this spherical
aggregate grabs the dirt particles and
you know it removes the dirt particles
as the water flows off this is how the
soap acts on clothes and cleans them
understood so this is something very
important that you must remember here is
in fact an experiment that you can
easily perform at home that tells you
you know about the formation of missiles
and the action of soap what so basically
does is it makes oil and grease dissolve
in water by forming spherical missiles
you know which trap the oil drops and
which then get dispersed in water so if
you take two mixtures of oil and water
initially you will see that the oil is
floating above the water because oil and
water don't mix now if you add some soap
in one of the test tubes you will see
that the oil and water will mix and they
will form a solution understood at least
they'll form a dispersed kind of
solution
so basically soap helps oil dissolve in
water or grease dissolve in water and
then when the water is washed off the
dirt also gets washed off that is how
soap works there you go a milky oil and
water emulsion is formed when soap is
added to the oil water mixture let's
solve a problem related to the action of
soap
take a look at the figure below
well this figure clearly depicts what we
had just studied it depicts the action
of soap on a dirt particle
what is being depicted in the figure
what is the large unevenly shaped
gray substance in the middle and what
are the thin strips sticking to it
what is the property of the sodium ion
end of the chains sticking to the gray
substance what is this we have formed by
the chains in the picture that are
surrounding the gray substance called
well this question has many parts but
all these parts are easy let's solve
each part one by one here's the picture
the first part says what is being
depicted clearly the removal of dirt
particles by soap is being depicted in
this picture you can see that different
soap molecules have surrounded the dirt
particle and they are trying to remove
the dirt particle what is the large
unevenly shaped gray substance in the
middle and what are the thin strips
sticking to it clearly the gray
substance in the middle is the dirt
particle the thin strips sticking to it
are the hydrophobic ends of the soap
molecules what is the property of the
sodium ion end of the chains sticking to
the gray substance well the property of
the sodium ion end of the chains is that
these ends are hydrophilic they attract
water that's the property of the sodium
ion end of the soap molecules what is
the sphere formed by the chains in the
picture that are surrounding the gray
substance called well the sphere that
the slope molecules form is definitely
called a missile there is no doubt about
it
isn't it so that's the final answer this
question had many parts but each part
was asking us you know only a simple
question about the action of soap under
particles let's now move on to the next
concept soap end hard water
you