Suppose if I have 10 grams of hydrogen
in this box.
in this box,
How many atoms of hydrogen will be
how many atoms of hydrogen will be
present in this 10 grams of hydrogen?
present in this 10 grams of hydrogen?
This can be identified by a mole
This can be identified by a mole
concept.To understand the mole concept,
concept.To understand the mole concept,
let us first understand a very simple
let us first understand a very simple
example of fruits. Suppose I want one
example of fruits. Suppose i want one
dozen of apples. How many apples should
dozen of apples. How many apples should
I get then?
I get then?
12 apples. Suppose if I want 1 dozen of
12 apples. Suppose if I want 1 dozen of
pineapples. How many pineapples should i
pineapples. How many pineapples should i
get? 12 pineapples. And if I want one
get? 12 pineapples. And if i want one
dozen of oranges, I should get 12 oranges,
dozen of oranges I should get 12 oranges,
but will the mass of 12 apples, 12
but will the mass of 12 apples, 12
pineapples and 12 oranges be equal? No.
pineapples and 12 oranges be equal? NO
The mass of 12 apples might be five
The mass of 12 apples might be five
Kgs. The mass of 12 pineapples might be
Kgs. The mass of 12 pineapples might be
10 Kgs. The mass of 12 oranges might be
10 Kgs. The mass of 12 oranges might be
3 Kgs. So, when we say one dozen,
3 Kgs. So when we say one dozen
the number means constant, but the
the number means constant, but the
mass depends upon which substance that
mass depends upon which substance that
we're taking. Now, the same concept we can
we're taking. Now the same concept we can
use by finding moles. If I tell you I
use by finding moles. IfIi tell you I
need one mole of hydrogen, how many
need one mole of hydrogen, how many
hydrogen atoms will it have? It will have
hydrogen atoms will it have? It will have
6.022 into 10 raise to 23 atoms of
6.02 2 into 10 raise to 23 atoms of
hydrogen in it, but if I tell you I want
hydrogen in it, but if i tell you i want
one mole of oxygen,
one mole of oxygen,
how many oxygen atoms would have? It will
how many oxygen atoms would have? It will
have 6.022 into 10 raise to 23 atoms of
have 6.02 2 into 10 raise to 23 atoms of
oxygen.
oxygen.
Similarly, if I tell you I want one mole
Similarly if i tell you i want one mole
of nitrogen, it will contain 6.022 into
of nitrogen it will contain 6.022 into
10 raise to 23 items of nitrogen. But
10 raise to 23 items of nitrogen, but
will the mass of all these atoms be
when the mass of all these atoms be
equal? No. Mass of 6.022 in 10 raise to 23
equal? NO. Mass of 6.022 in 10 days to 23
atoms of hydrogen will be 1 gram. That is
atoms of hydrogen will be 1 gram. That is
because the atomic mass of hydrogen is
because the atomic mass of hydrogen is
one unit. Then, mass of 6.022
one unit. Then mass of 6.022
into 10 raised to 23 atoms of oxygen will
into 10 raised to 23 atoms of oxygen will
be 16 grams because atomic mass of
be 16 grams because atomic mass of
oxygen
oxygen
is 16 units. And, mass of 6.022 into 10
is 16 units. And mass of 6.022 into 10
raise to 23 atoms of nitrogen will be 14
raise to 23 atoms of nitrogen will be 14
grams because atomic mass of nitrogen is
grams because atomic mass of nitrogen is
14 units. So, one mole of any element will
14 units. So one mole of any element will
have fixed number of atoms in it, that is
have fixed number of atoms in it, that is
6.022 into 10 raise to 23,
6.022 into 10 raise to 23
but the mass will depend upon the atomic
but the mass will depend upon the atomic
mass of that element. So, 6.022
mass of that element. So 6.022
into 10 raised to 23 is a fixed number which
into 10 raised to 23 is a fixed number which
was given by Avogadro. So, this number
was given by Avogadro. So this number
is called have avogadro number. Now, when
is called have avogadro number. Now when
we check the atomic masses here of the
we check the atomic masses here of the
elements, they are written in grams. So, you
elements, they are written in grams. So you
are right now, these masses are called
are right now, these masses are called
the molar masses. The mass of one mole of
the molar masses. The mass of one mole of
each element. So, molar mass of hydrogen
each element. So molar mass of hydrogen
is one gram. Molar mass of oxygen is 16
is one gram. Molar mass of oxygen is 16
grams and more mass of nitrogen is 14
grams and more mass of nitrogen is 14
grams. So, we can define molar mass as,
grams. So we can find molar mass as
the atomic mass or molecuar mass of
the atomic mass or molecuar mass of
substances expressed in terms of grams
substances expressed in terms of grams
is called molar mass. Now, let's take
is called molar mass. Now let's take
the example of nitric acd. If I tell you
the example of nitric acd. If i tell you
I want one mole of nitric acid, how many
i want one mole of nitric acid, how many
nitric acid molecules will be present in
nitric acid molecules will be present in
it?
it?
There will be 6.022 into 10 raised to 23
There will be 6.022 into 10 raised to 23
molecules of HNO3 present in one mole
molecules of HNO3 present in one mole
of nitric acid. What will be the mass of
of nitric acid. What will be the mass of
one mole of nitric acid then? Mass of one
one mole of nitric acid? Then mass of one
hydrogen is one unit, mass of one
hydrogen is one unit, mass of one
nitrogen is 14 units and mass of one
nitrogenous 14 units and mass of one
oxygen is 16 units and there are three
oxygen is 16 units and there are three
oxygens present in the formula. So, total
oxygens present in the formula. So total
mass of HNO3 is 63 units. So, molar
mass of HNO3 is 63 units. So molar
mass of HNO3 will be 63 grams.
mass of HNO3 will be 63 grams.
So, one mole of hno3 will have 6.022
So one mole of hno3 will have 6.02 2
into 10 raised to 23 molecules of hno3,
into 10 raised to 23 molecules of hno3,
which is nothing but equal to 63 grams.
which is nothing but equal to 63 grams.
Similarly, if I tell you how many
Similarly if I tell you how many
molecules of hydrogen will be present in
molecules of hydrogen will be present in
one mole of hydrogen molecules. It will
one mole of hydrogen molecules. It will
be 6.022
be 6.022
into 10 raised to 23 molecules of
into 10 raised to 23 molecules of
hydrogen, but what will be the molar mass
hydrogen but what will be the molar mass
of molecules of hydrogen. It will be one
of molecules of hydrogen. It will be one
plus one that is two grams because here we are
plus one is two grams because you're
talking about H 2 the molecule. If we
talking about 2 molecule. If we
talk about hydrogen atoms it is going
talk about hydrogen atoms that is going
to be 1 gram, but because we are talking
to be 1 gram, but because we are talking
about hydrogen molecule is going to be
about hydrogen molecule is going to be
two grams.
two grams.
Similarly, in nitrogen molecules, if we
Similarly in nitrogen molecules if we
have one mole of nitrogen molecules, it
have one mole of nitrogen molecules it
would contain 6.022 into 10 raise to 23
would contain 6.022 into 10 raise to 23
molecules of nitrogen, whose mass is going
molecules of nitrogen, whose mass is going
to be 28 grams because the molar mass of
to be 28 grams because the molar mass of
nitrogen atoms is 14 grams. But, molar
nitrogen atoms is 14 grams. But molar
mass of nitrogen molecules will be
mass of nitrogen molecules will be
double, that is, 28 grams because nitrogen is
doubl,e that is, 28 grams because nitrogen is
N2. Thus if I tell you one mole of
N2 Then if I tell you one mole of
ozone layer will contain how many ozone
ozone layer will contain how many ozone
layer molecules? It will contain 6.022
layer molecules? it will contain 6.022
into 10 raised to 23 molecules of O3, but what
into 10 raised to 23 molecules of O3, but what
will be a mass of one mole of ozone? It
will be a mass of one mole of ozone? It
will be 3 into 16 units, that is nothing
will be 3 into 16 units, that is nothing
but 48 grams. So, molar mass of ozone is going to
but 48 grams. So molar mass of ozone is going to
be 48 grams. Now, suppose if I tell you, I
be 48 grams. Now suppose if I tell you I
have 1 mole of nitrogen molecules, how
have 1 mole of nitrogen molecules, how
many molecules will be present in one
many molecules will be present in one
mole? 6.022 into 10 raise to 23 molecules
mole? 6.022 into 10 raise to 23 molecules
of nitrogen, that means we have 6.022 into
of nitrogen, that means we have 6.022 into
10 raised to 23 N2 is present.
10 raised to 23 N2 is present.
So, how many atoms will be present in
So how many atoms will be present in
this one mole of nitrogen molecule?  Twice
this one mole of nitrogen molecule?  Twice
the number, which is nothing but equal to
the number which is nothing but equal to
12.044 into 10 raise to 23 atoms,
12.04 4 into 10 raise to 23 atoms,
because nitrogen molecules are N2,
because nitrogen molecules are N2,
that means two, two atoms together. Let
that means to all to atoms together. Let
us solve some question based on mole
us solve some question based on molar
concept. Calculate the number of moles
concept. Calculate the number of moles
for the following: 52 grams of helium
for the following: 52 grams of helium
and 12.044 into 10 raise to 23 number
and 12.04 4 into 10 raise to 23 number
of helium atoms.
of helium.
Now, first of all you have to understand
The first of all you have to understand
the question. Here, you have been provided
the question. Here, you have been provided
in the first sub question 52 grams of
in the first sub question 52 grams of
helium. You have to calculate for 52
helium. You have to calculate for 52
grams of helium will be how many moles?
grams of helium will be how many moles?
It is just like calculating, if you have
It is just like calculating, if you have
10 kgs of bananas,
10 kgs of bananas
how many dozens of bananas will you have?
how many dozens of bananas will you have?
So, for finding out the solution to any
So for finding out the solution to any
such questions in mole concept, the
such questions in mole concept, the
first step will be
first step will be
you have to find out one mole of that
you have to find out one mole of that
element will have how many atoms first.
element will have how many atoms first.
So, one mole of helium will be equal to
So one mole of helium will be equal to
6.022 into 10 raise to 23 atoms of
6.022 into 10 raise to 23 atoms of
helium. How much will this one mole weigh? Now,
helium. How much will this one mole be? Now
helium's atomic mass is four unit, so one
helium atomic masse is four unit, so one
mole of helium will be four grams. So, my
mole of helium will be four grams. So my
entire formula becomes one mole of helium
entire formula becomes one mole of helium
is equal to 6.022 into 10 raise to 23 atoms
is equal to 6.022 into 10 to 23 atoms
of helium, which is equal to four grams.
of helium which is equal to four grams.
Now, the next step will be, you have to
Now the next step will be you have to
calculate the number of moles and you
calculate the number of moles and you
have to take moles as X. So, we will
have to take moles as X, so we will
write, let the number of moles of helium
write like the number of moles of helium
be X in 52 grams of helium. So, we have to
be X in 52 grams of helium. So we have to
continue the question in the statement.
continue the question in the statement.
Now, whatever you have written in the
Now whatever you have written in the
statement, you have to convert it in the
statement, you have to convert it in the
form of an equation. So, the equation
form of an equation. So the equation
becomes X moles of helium is equal to 52
becomes X moles of helium is equal to 52
grams of helium. Now, in the equation on the
grams of helium. Now in the equation on the
left-hand side you have X moles. So, you
left-hand side you have X moles, so you
check your first step,
check your first step
where do you find moles. One mole. So, just
where do you find moles. one mole. So just
one mole about this x mole and in
one mole about this x mole and in
the equation that we have formed on the
the equation that we have formed on the
right-hand side we have 52 grams of
right-hand side we have 52 grams of
helium. So, check in the first step
helium. So check in the first step
where do you find grams, four grams. So,
where do you find grams, four grams. So
that four grams above 52 grams of helium.
that four grams about 52 grams of helium.
Thus we have formed
That's we have formed
an equation saying, if one mole is equal
an equation saying if one mole is equal
to four grams of helium, then X moles
to four grams of helium then X moles
will be equal to 52 grams of helium. So, for
will be equal to 52 grams of helium. So for
finding out x we have to cross
finding out x we have to cross
multiply them. So, after cross-multiplying we
multiply them. So, after cross-multiplying we
get x is equal to 52 upon 4, which is
get x is equal to 52 upon 4, which is
equal to 13 moles. Thus, 52 grams of
equal to 13 moles. Thus 52 grams of
helium will have 13 moles. Now, let's
helium will have 13 moles. Now let's
come to the second question. In the
come to the second question. In the
second question we have 12.044 into 10
second question we have 12.04 4 into 10
raised to 23 number of helium atoms. We
raised to 23 number of helium atoms. We
have to find out the number of moles
have to find out the number of moles
present in these helium atoms. It is just
present in these helium atoms. It is just
like calculating the number of dozens in
like calculating the number of dozens in
12.04 into 10 raised to 23 bananas. So, the
12.04 into 10 raised to 23 bananas. So the
first step will be 1 mole of helium is
first step will be 1 mole of helium is
equal to 6.022 into 10 raised to 23
equal to 6.02  into 10 raised to 23
helium atoms, which is equal to four
helium atoms, which is equal to four
grams. The second step will be,
grams. The second step will be,
let the number of moles be X in 12.044
let the number of moles be X in 12.04 4
into 10  raised to 23 number of helium atoms. Now,
into 10  raised to 23 number of helium atoms. Now
in the next step we will be converting
in the next step we will be converting
our statement into an equation for. So, X
our statement into an equation for. So X
moles is equal to 12.044 into 10 raised to
moles is equal to 12.04 into 10 raised to
23 helium atoms. Now, in our equation on
23 helium atoms. Now in our equation on
the left-hand side we have X moles, when
the left-hand side we have X moles, when
we check our first step. In the first
we check our first step. In the first
step where do we have moles? It is one
step where do we have modes? It is one
mole, so we write one mole about the X
mole, so we write one mole about the X
moles and in that equation on the right
moles and in that equation on the right
hand side we have 12.044 into 10  to 23
hand side we have 12.04 4 into 10  to 23
number of helium atoms. So, when we take a
number of helium atoms. So when we take a
first step
first step
where do we have number of atoms, in the
where do we have number of atoms, in the
center, that is,  6.022 into 10 raised to 23. So,
center, that is,  6.022into 10 raised  to 23. So
we write 6.022 into 10 raised to 23 about 12.044 into
we write 6.022 into 10 raised to 23 about 12.04 into
10 raised to 23. Thus, our equation becomes, if
10 raised to 23. Thus, our equation becomes if
one mole of helium will contain 6.022
one mole of helium will contain 6.022
into 10 raised to 23 helium atoms, then x mole
into 10 raised to 23helium atoms, then x more
of heliums will contain 12.044 into 10
of helium's will contain 12.04 4 into 10
raised to 23 number of helium atoms. So, when
raised to 23 number of helium atoms. So when
we cross multiply, we find the answer x
we cross multiply we find the answer x
is equal to 2. So, that means in 12.044
is equal to 2. So that means in 12.04
into 10 raised to 23 helium atoms, the number
into 10 raised to 23 helium atoms. The number
of moles are two. Let us solve  one more
of moles are two. Let us solve  one more
question. Calculate the mass of the
question. Calculate the mass of the
following; 0.5 moles of nitrogen gas.
following 0.5 moles of nitrogen gas.
Now, here we are going to calculate the mass
Now you're going to calculate the mass
of 0.5 moles of nitrogen gas. So, our
of 0.5 moles of nitrogen gas. So our
first step will be, 1 mole of nitrogen
first step will be 1 mole of nitrogen
gas is equal to 6.022 into 10 raised to
gas is equal to 6.022 into 10 raised to
23 molecules of nitrogen, because we are
23 molecules of nitrogen, because we are
talking about N2, which is equal to 28
talking about N2 which is equal to 28
grams because 1N is14 grams, two Ns will
grams because 1N is14 grams, two will
be 28 grams. Now, the next step is we have
be 28 grams. Now the next step is we have
to take masses X. So, let the mass be X
to take masses X. So let the mass be X
grams for 0.5 moles of N2 gas. Now, in the
grams for 0.5 moles of N2 gas. Now in the
next step we will be converting our net
next step we will be converting our lel
statement into equation form. So, we get x
statement into equation form. So we get x
grams is equal to 0.5 moles. Now, on the
grams is equal to 0.5 moles. Now on the
left-hand side of the equation we have x
left-hand side of the equation we have x
grams and in our first step
grams and in our first step
where is the gram symbol, we have 28
where is the gram symbol we have 28
grams. So, we write 28 grams about X grams
grams. So we write 28 grams about X grams
and on our right hand side we have 0.5
and on our right hand side we have 0.5
moles of N2 gas and in the first step
moles of N2 gas and in the first step
where do we have mole, we have one mole.
where do we have mole, we have one mole.
So, we write one mole about 0.5 moles. So, our
So we write one mole about 0.5 moles that
equation becomes if 28 grams is equal to
equation becomes if 28 grams is equal to
1 mole of nitrogen gas then X grams will
1 mole of nitrogen gas then X grams will
be equal to 0.5 moles of nitrogen gas.
be equal to 0.5 moles of nitrogen gas.
That's when we cross multiply we get
That's when we cross multiplyy we get
x is equal to 14 grams.
x is equal to 14 grams.
