
English: 
good morning let's look at what is mean
by
formula mass formula mass
is the mass of
individual mass of
an individual molecule or formula unit
formula mass is also known as molecular
mass
or molecular weight
so to calculate the formula mass you
need to
do the sum of masses of atoms in a
single molecule
or the formula unit let's let's look at
an example
so mass of
one molecule
of water
the molecular formula of water is h2o

English: 
Good Morning. Let's look at what is mean by formula mass.
Formula mass
is the mass of individual
mass of an individual molecule
or formula unit
formula mass is also known as molecular mass or molecular weight
so to calculate the formula mass you need to
do the sum of the masses of the atoms
in a single molecule
or the formula unit
Let's look at an example
Mass of  one molecule of water
The molecular formula of water is H2O

English: 
so that is equal to 2 multiplied by
1.01
atomic mass unit that is a
mass of hydrogen atomic mass of hydrogen
plus 16 point
zero atomic mass
unit of oxygen so
what we get is 18.02
atomic mass unit so you can calculate
the mass of molecule by
doing the sum of the masses of the atoms
in a single molecule or formula
unit so let's look at
what is molar mass of compounds molar

English: 
so that is equal to
 
two multiplied by one point
zero one atomoic mass

English: 
mass of the compound
is a relative masses of molecules that
can be calculated from
atomic masses so
i mentioned that the formula mass
formula mass of water h2
is equal to 18.02
atomic mass unit
so molar mass of
h2o is equal to
one mole of
h2

English: 
is equal to 18.02
gram per mole
of s2 so you can determine the
molar mass from the
formula mass of s2o
also we need to know that one more of
h2o contains so one more of
h2 is equal to
six point zero
two two multiplied by ten raised to
twenty three
more problem from how many moles are in
15.0 gram of lead oxide

English: 
so lead oxide atomic mass of uh
lead pb is led is to 207.2 gram
per mole and the atomic mass of
oxygen is 16.00 gram per
mole so let's look at how we solve this
problem
so when you are solving the problem
first thing what you need to write
is uh what is given
so what is given here is 15
point zero gram
of lead oxide
and what you need to find here
you need to find
how many moles
moles of
plate oxide okay now what's your plan

English: 
here
so what is your plan
so first you will because you have the
gram of led oxide
you'll convert the gram of lead oxide
to mole of lead oxide
okay to do that you know that
what is the relationship for the
relationship
relationship that you can use in this
equation is
one mole of
lead oxide
is equal to the molar mass of lead oxide
so first you need to calculate the

English: 
molecular mass of lead oxide how will
you calculate molecular mass of blood
oxide
so lead is
207.2
atomic mass unit oxygen
there are two oxygen right two 2
multiplied by
oxygen is equal to
that is a 16 multiplied by 16.00
multiplied by 2 so that is a 32.00
amu so mass of
molar mass of light oxide is 239.2
amu so relationship is
one mole of lead oxide is equal to 239.2

English: 
gram of dioxide
okay so one mole of lead oxide is a 239
gram of
lead oxide so let's look at here so how
will you solve this problem
so solution
so you have 50.0
gram of lead oxide
and you know that one mole of lead
outside is 239.2 gram of lead oxide so
we'll convert that multiply by one mole
of
leather oxide divided by
239 point

English: 
2 gram of lead oxide
okay so here
the gram and gram will get cancelled
and what you will get
is uh and you might
do calculation so you'll get
50 divided by 239.2
so you get 0.2
modes so you can look at that
there are three significant figures here
given this is what is the given here so
one two and three three significant
figure here so
you make sure that you have one
two three or you can underline
the significant figure here so your
answer is

English: 
0.209
mole of lead oxide
so let's look at another problem here
what is the mass
of 4.78
multiplied by 10 raised to 24 no2
molecules
question is what is the mass of 4.78
multiplied by 10 raised to 24
no2 molecule
so what is a again let's see what is
given here so
given

English: 
7 4.78 multiply by 10 raised to 24
no2 molecules
you need to read the question and write
what is given
then write what you need to find
what you need to find here is
how many grams of how many gram
of an o2 molecule
okay so what's your plan here
to do this first you have
given the molecules
you need to con you need to convert the
molecules

English: 
to how many more molecules of
no2 to more
of no2
then convert that to gram
of no2
okay so you have
you wrote down what is given you wrote
what is your plan
and then try to find the relationship
that
you can able to use to solve the
problem so like i said
so what's the relationship you can use
to relationship
first you need to do the molecular
formula
of uh no2 so you can calculate the
molecular formula of no2
so um
no2 so 1
1 nitrogen right so four

English: 
one fourteen point
zero one atomic mass unit
so you ask from where i am getting this
number you can look at the
periodic table this is the atomic mass
of nitrogen
so now there's two oxygen here so two
multiplied by oxygen atomic mass of
oxygen is 16.00
mu so you can add
that 32.00
so you can get 46.01
am okay 46.01 amu
so the relationship is uh
one more of no2
equal to

English: 
46.01
gram of no2
okay and that equal to 6.022
multiplied by 10 raised to 23
molecules of no2
6.022 multiplied by 10 raised to 23 is
called the
avogadro's number so so one mole of no2
contains 6.022 multiplied by 10 raised
to 23
molecules of and let's now look at the
how we solve these problems so solution
so 4 there are 4.78
multiplied by 10 raised to 24

English: 
no2 molecules
multiplied by so you can see that one
mole of no2 is six point zero two to
multiply by 10 raised to 23
molecules of energy so so one more of
no2 divided by
6.022
multiplied by 10 raised to 24
sorry 10 raised to 23
make sure that you write the correct
thing
10 raised to
23 molecules
of no2
multiplied by now we are converting that
into grams so 46.01

English: 
gram of no2
divided by one
mole of inorder
okay so here what's happening here that
you can cancel out
uh no2 molecules and no2 molecules
and also you can cancel out more of no2
versus small of no2
so when you multiply here so 4.78
multiplied by 10 raised to 24
um multiplied by 46.01
gram of no2 divided by 6.0 to 10 raised
to 23.
uh that will be in a gram of no2 so you
can see
what you can get here so you'll end up
having
so there's a three sig fig here so
answer should be
in three six six so 365
gram of anode
