Molecular Mass & formula Unit mass - Atoms & Molecules, Force & Laws of Motion, Science, Class 9 Video Lecture

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till now we have seen the molecular mass
of atoms for example we know the
luminous mass of hydrogen carbon oxygen
these things we know right it is all
units but most of the things around us
is compound for example water carbon
dioxide sulfuric acid ammonia gas
methane yes all these are confirmed and
we want to find the mass molecular mass
of compounds so let's try to find water
water has one hydrogen sorry two
hydrogen and one oxygen what is the
molecular mass of one hydrogen one unit
what is the molecular mass of one oxygen
16 units so total you will see 2 plus 16
is 18 units pretty easily with this you
can find a molecular mass of water just
now we have studied see we know the
molecular mass of all these atoms we
know the the you know that with the
formal law chemical formula you can
actually the chemical formula actually
tells the constituents of this
particular molecule number of atoms it
has so if I know the mass of hydrogen
mass of oxygen I can actually find the
mass of or what see it is just like that
if I know mass or weight of all the
students in the class let's suppose they
are five in the class student a b c d
student a is a girl with 30 kg weight b
is again a girl with 35 kg weight c is a
boy with 40 kg weight DS will be fat boy
with 45 kg weight and
is very fat guy with 50 kg weight little
small class maybe fifth or second I want
to find the total weight of the class I
have to just sum these that's all you
add all these 90 plus 35 135 170 202
only the total weight of the class
similarly if I know the weight of all
these atoms I can easily find the weight
on this whole molecule because we know
that one molecule is composed of these
many atoms let's take some more examples
it's TIG nitric acid I want to find the
weight of nitric acid nitric acid has
one hydrogen plus one nitrogen
last three oxygen so let's add this one
hydrogen is one one nitrogen is 14 3
oxygen is 16 into 3 3 into 16 so how
much you get 63 unit ok it easy so let's
take some more examples in fact this is
what we have done now the native
molecular mass of water I'm going to
guess we just formed for water it was
one hydrogen two hydrogen so 2 into 1
plus 1 oxygen 1 into 16 18 units and for
nitric acid we just on one nitrogen 1
nitrogen
3 oxygen so 1 hydrogen is what point to
one one nitrogen is what 1 to 14 oxygen
is 16 where 8 48 plus 15 plus 3 63
okay so that let's talk about a term
called formula unit mass same as the
molecular mass for a compound just a new
name given formula unit mass of a
substance is I think where the sum of
atomic mass of all the atoms in the
formula for example I have the formula
h2o this formula whatever happens you
have you add all the atomic mass then it
of the following mass weight typically
formula advanced this term is used for
ionic compounds example you have it
suppose po4 3 minutes want to find the
muscles okay or let suppose like NaCl
yeah NSA is I think important I want to
find the formula unit mass so that is
one sodium plus 121 sodium is 123 121
35.5 you are there to create fine fine
do it okay so it just a new down thus
now we form with the value of formulated
ones for NaCl 23 and this is 35 25 and
this 15 point 5 unit let's find for
calcium chloride cacl2 this is also
annex we'll use it on formula mass for
this as well so it has one calcium
what's to clean
this 14 plus 2 into 35.5 that is 40 plus
71 with this 111 unit okay
and six equations you define the
molecular mass of these compounds they
all compounds hydrogen to hydrogen to
into 1/2 unit
let's do something here only oxygen to
oxygen 2 into 16 32 units chlorine two
chlorine atoms 2 into 35.5 that is 71
minutes you can just use this later or
you can write it then we have co2 one
carbon plus two oxygen carbon is what
how much 12 units two oxygen is how many
units 16 units solve rate 32 plus 12 44
generates with him ch4 one carbon plus
one hydrogen 1 carbon is what you want
into 12 4 hydrogen is what 4 into 100
each is one it we solve this to a plus
for six nearly done C do a six two
carbon plus 6x2 into one carbonate is 12
unit six into one and you saw all this
you get 24 plus 6/13
okay c2h4 two carbon plus four hydrogen
saw this 2 into 12 plus one 128
ns3 nitrogen is 14 hydrogen 3 hydrogen 3
14 plus 3 is 17 minute
similarly ch3oh last one has one carbon
four hydrogen and one oxygen let us put
the value of one carbon is 12 4 hydrogen
is 4 into 1 4 1 oxygen is 16 16 + 4 xx +
13 32
so you can easily find the molecular
mass of all these let's take America we
have to find the formula unit mascot
Gellin ona - ok - 0 3 C formula unit
mass is viewed because all ionic
compounds it is also giving the atomic
mass of zinc sodium potassium carbonate
of cringing pretty easy then right so
let us find 2 then office it has one
zinc one oxygen
one think is almost 65 plus one oxygen
are 16 4 add this a demodulator ii na 2
O 2 sodium one oxygen sodium is so much
already 23 so to integrate easily
because there to saudi minutes plus 1
into oxygen oxygen is 16 minute you
solve this 46 plus sixteen sixty two
minutes K 2 Co 3 K 2 Co 3 2 potassium 1
carbon 3 obviously right to potassium
one carbon to your spirits put the
values 2 into potassium is 39
plus 1into carbon is 12 plus 3 into
oxygen 16 saw this 48 plus 12 60 plus 78
138 unit and that is it easy okay
so having understood the molecular mass
let's understand the whole concept I
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