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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