gram
## Calculating gram formula mass

hi I'm going to show you guys how to

calculate the gram formula mass what you

need to do when you get something like

this is you first need to look use the

periodic table to find out the mass of

one mole of each of these different

elements so what we did is we use the

periodic table and it shows that zinc

has a 60 foot one mole of zinc equals 65

grams and one mole of the other guy's

equal these numbers over here alright so

once you got that the first thing you

need to do is you want to actually use

this formula and multiply the the ratio

by these numbers so what I mean is let's

look I have one zinc here so I'm gonna

add this so I'm gonna use the periodic

table find the mass of zinc and I'm

gonna write it right over here I've got

65 grams for zinc Plus this whole thing

now this whole thing is equal to 2 times

12 for carbon plus 3 times 1 for

hydrogen plus 2 times 16 for oxygen so

I'm going to say 2 times 16 okay when

you add up all those numbers you get 59

grams well this whole thing okay is

actually gonna be multiplied by 2

because there's a 2 here if there's a 3

here I would add 3 multiply it by 3 then

we're going to take that number and add

that number to 2 times whatever this is

now this is a hydrate what this means is

that there are two this doesn't not does

not mean multiply this times that it

means that there are two water's bonded

to this large thing so what I need to do

is add up the value of the two waters

and add them to the total mass of this

compound so one water is equal to 18

grams so two waters would equal to 32

I'm sorry 36 so it's going to be two

times

eighteen added to it okay so now I'm

gonna get out my calculator and I'm

gonna add 65 plus fifty nine times two

plus two times 18

and they get a number of 219 so what

this is telling me is that one mole of

this large molecule I'm sorry this large

compound is equal to 219 grams okay now

what if I had something else let's say I

had a different I had a different

compound and it was a little more

complicated or maybe even easier what if

I had something like I'm trying to find

out what the mass of calcium hydroxide

is okay what I would do here is I would

use the periodic table to find out what

the mass of that is in one mole on the

periodic table of calcium is equal to 40

grams now this is the parentheses now

oxygen what I just showed you earlier

was equal to 16 grams so it's this plus

this plus another hydrogen right there

which is one gram but this whole section

right here is multiplied by two so what

I've got is I've got 40 grams plus 2

times 17 which is 34 grams so I'm at 1

mole of calcium hydroxide would equal to

74 grams I hope that helped have a good

day

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