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in this video we're going to focus on
finding the molar mass of a compound so
let's start with the basics what is the
molar mass of Elemental nitrogen that
nitrogen as a diatomic molecule but as
an atom well if you go to the periodic
table you'll see two numbers the atomic
number of seven and the average atomic
mass of fourteen point zero one the
molar mass is equivalent to this number
it's fourteen point zero one grams per
mole the molar mass is basically it
connects mass with moles so that's the
molar mass of n it's fourteen point zero
one grams per mole so what that means is
that one mole of nitrogen has a mass of
fourteen point zero one grams so let's
say if we wanted to find the molar mass
of atomic fluorine fluorine has an
atomic number of nine but a mass number
of 19 so this is the molar mass of
fluorine it's 19 grams per mole so every
mole of fluorine atoms has a mass of 19
grams now what about some other
molecules for example let's find the
molar mass of oh three this is ozone is
found in the upper atmosphere and sa
elemental sulphur find the molar mass of
these molecules o3 contains three oxygen
atoms now if you go to the periodic
table and you look for the average
atomic mass of oxygen you can see two
numbers 8 and 16 the larger of these two
is always the molar mass so the atomic
mass of oxygen is 16 if you multiply by
3 that's 48 so the molar mass of ozone
o3 it's 48 grams per mole now what about
the molar mass of sulfur F 8 so what we
have is 8 sulfur
and the average atomic mass of each
sulphur atom is 32 point zero 7 so what
we need to do is multiply 32 point zero
seven by eight and so this will give us
the molar mass of sulfur it's 256 point
five six grams per mole so as you can
see it's very easy to calculate the
molar mass of something but let's try
some harder examples go ahead and find
the molar mass of carbon dioxide perhaps
you've seen it as dry ice and also
silicon tetrafluoride so feel free to
pause the video and try these examples
so CL 2 contains one carbon atom and two
oxygen atoms now the atomic mass of
carbon is twelve point zero one and
oxygen is 16 so 2 times 16 and that's 32
and 32 plus 12 is 44 so the molar mass
of carbon dioxide is 44 point zero one
grams per mole now let's do the same
thing for silicon tetrafluoride so we
have a single silicon atom and four
fluorine atoms the atomic mass of
silicon is twenty eight point zero nine
the average atomic mass of fluorine is
19 19 times four is 76 now let's add
that to twenty eight point zero nine
so therefore the molar mass of silicon
tetrafluoride is 104 point zero nine
grams per mole so this is the answer
now let's work on another example that
has more elements c6h12o6 this is
glucose perhaps you've seen it in bio
it's basically a molecule that provides
energy for sales so go ahead and
calculate the molar mass of glucose so
we have six carbon atoms 12 hydrogen
atoms and six oxygen atoms what I'd like
to do is I'd like to separate the
elements so there's as you can see
there's a process in which I like to
calculate the molar mass each carbon
atom has an atomic mass of 12.01 and
each hydrogen atom if you look at the
periodic table it's one point zero zero
eight and we've seen oxygen multiple
times so we know the atomic mass is 16
now six times twelve is seventy-two and
six times point zero one is point zero
six twelve times one is 12 12 times 8 is
96 so this is going to be point zero
nine six and six times 16 is also 96 so
now all we need to do is simply add
these numbers together
so the answer that I have is 180 0.156
grams per mole so that's the molar mass
of glucose a typical monosaccharide
sometimes you may need to find the molar
mass of a substance for which you're not
given the chemical formula like this one
what is the molar mass of calcium
phosphate before we could find it you
gotta write the formula so you need to
know that calcium phosphate is an ionic
compound it's composed of a metal and
some nonmetals so we need to find the
charges calcium has a positive 2 charge
it's in group 2 of the periodic table
and phosphate is just one of those
polyatomic ions you need to know so the
formula is going to be ca3 po4 2 you
need to switch to charges with the
subscripts and reverse them so this
substance has three calcium atoms two
phosphorus atoms and eight oxygen atoms
two times four is eight
now each calcium atom has an atomic mass
of 40 point zero eight phosphorus is
thirty point nine seven and oxygen has
an atomic mass of sixteen now three
times 40 is 120 point zero eight times
three is point two four two times thirty
point nine seven that's going to be 61
point nine four and eight times 16 is
128 so now we just need to add these
three numbers
so I got 310 point 18 grams per mole so
that's the answer that's the molar mass
of calcium phosphate so here's another
example like the last problem in this
problem the other writes the chemical
formula first before you can find the
molar mass so what is the chemical
formula of vanadium 5 hydrogen phosphate
so vanadium is a metal hydrogen
phosphate is a polyatomic ion composed
of Na metals so we have an ionic
compound again now the Roman numeral
tells you the charge on vanadium so in
this example vanadium has a positive 5
charge hydrogen phosphate is hpo4 you
have a hydrogen attached to a phosphate
molecule phosphate is po4 the negative 3
charge hydrogen is h+ when you combine
these two you get hydrogen phosphate
which is hpo4 and then you add 1 and
negative 3 and that will give you
negative 2 so that's the chemical
formula of the hydrogen phosphate
polyatomic ion now let's use the same
method to write the formula of this
substance so it's going to be v2
hpo4 times 5
whenever you have multiple polyatomic
ions within a compound you need to
enclose it inside a parentheses so now
that we have the chemical formula of an
18-5 hydrogen phosphate we can now
calculate the molar mass so we have 2
vanadium atoms and then we have run
times 5 so 5 hydrogen's 1 times 5 5
phosphorus atoms and then 4 times 5 20
oxygen atoms
so now let's look at vanadium in the
periodic table vanadium has an atomic
mass of fifty point nine for hydrogen is
one point zero zero eight phosphorous
thirty point nine seven and oxygen 16
so first let's multiply two by fifty
point nine four so that's 101 point
eight eight and then five times one
point zero zero eight that's going to be
five point zero four and then five times
thirty point nine seven
that's 150 four point eight five and
twenty times 16 is 320 so now let's add
up these four numbers
so I got 580 one point seven seven grams
per mole so that's the molar mass of
vanadium 5 hydrogen phosphate
