Expressing Concentrations of Solutions (Mass, Volume) Video Lecture | Chemistry for JEE Main & Advanced

welcome to electron line and in this
video we're going to take a look at how
to express the concentrations of
solutions so we're talking about how
much solute there is in the solution and
there's various ways of doing that and
in addition to the ones I'm going to
describe here in this video we also can
talk about molarity and molality and all
kinds of different ways of how to
express concentration so we'll take them
one at a time but what we're going to do
here is talk about three very
significant ways of expressing the
amount of solute you have in a solution
and we can do it by doing weight in
weight volume in volume or weight in
volume what that means here is that we
can express in terms of how much mass or
how many yeah how many grams of the
solute we have in how many grams of the
total solution or we could talk about it
how much volume of the solute we have in
the total volume of the solution or we
can talk about in terms of how many
grams of the solute we have in so much
volume of the solution and remember it's
always in terms of the solution we have
this many grams in that many grams of
solution this many volumes this many
milliliters in that many milliliters of
solution and this many grams in this
many milliliters of solution it's always
in reference to how much solute we have
in the total solution but then in order
to prepare those solutions well we have
to talk about how to actually do that
because we don't want to start with the
end volume because when we add solute to
that we'll have more than the end volume
and so forth so we'll get it in just a
moment so hopefully through some easy
examples I could show you what we're
talking about here so let's say we take
10 grams of salt and we add it to 190
grams of water well when you add the two
together we'll have 200 grams of
solution and so what we talk about then
is how many grams of salt we have in the
total grams of solution and if we then
the 510 grams by 20 grams of 200 grams
and then multiply by a hundred we end up
with a 5 percent weight to weight
solution so that's what that means so
what you don't want to do when you're
preparing a solution is start with
adding 10 grams of salt to 200 grams of
water because then you'll end up with
210 grams of solution so what you do is
you have enough grams of the solute
- enough grams of the water to end up
with the total number of grams of the
solution you wanna end up with so in
this case 10 grams is a greater
percentage out of 190 grams and 5% that
the game we don't want to compare it to
this - the solvent we want to compare it
to the solution all right talk about
volume of solute - volume of solution a
good example is that of alcoholic
beverages how men is the percentage of
alcohol as a percentage of the total
volume of the solution so in this case
let's say we have 50% alcohol which by
the way is a hundred proof which is very
very strong of course 50% alcohol means
that we have 50% alcohol to the 100%
solution or one half of the solution is
alcohol by volume so we say 50% volume
to volume solution and if we add if we
have a solution where 75% of the total
solution is alcohol we'd say then we
have 75% to 100% solution or it's 75%
volume to volume solution not a lot of
you're not going to find a lot of
alcoholic beverages that are 75 percent
alcohol all right now let's say the
third one we have example 3 here we're
going to add a certain amount of weight
to certain amount of volume of solvent
to end up with a certain amount of
volume of solution usually you want an
end volume of solution so for example if
we have a saline solution at the
hospital where we take let's say these
leader bags of solution they put a
certain amount of salt in them so that
they can intervene asleep it that into
your bloodstream to add suit to add
liquid and to add salt into your
bloodstream and the way that is done is
they add two grams to a certain amount
of water to end up with a certain amount
of the solution well in the case of the
saline bags it's use your whole liter
now 100 milliliters but a thousand
milliliters but let's say you want to
produce a 2% weight 2 volume solution so
what you do is you add 2 grams to a
certain amount of water or better yet
you start with 2 grams of salt and you
add enough water to it until you have a
hundred milliliters of solution so that
at that point you have two grams of salt
in a hundred milliliters of solution
which is then a 2
cent wait to volume solution so you
don't start with 100 milliliters of
water you add enough water to the salt
to end up with a hundred milliliters of
solution and typically we use it we look
at it in terms of how many grams for how
many hundred milliliters you have and
that's how you get the percent solution
so in this case two grams added to 100
milliliters is a two percent solution we
can also look at in terms of parts per
thousand or parts per million or parts
per billion now we use that when the
concentrations are very very slight and
so parts per thousand means that you
have one gram per liter of solution
parts per million means you have one
gram per thousand liters of solution
which is a one one thousand of a gram or
a milligram per liter and finally parts
per billion means that you have one
grams per 1 million liters or one
microgram per liter so very very small
quantities so that's another way
expressing things in terms of weight per
volume and so we talk about how many
grams or how many liters or how many
grams for how many milliliters so those
are three of the main ways in which you
express concentrations of solutions and
of course we'll see some other examples
of that later so let me come up with
some good examples to make this very
clear to you and then we'll also talk
about Malathi and molarity later in some
later videos