okay let's take a look at a problem regarding gravimetric analysis. so the
question is is zero point four five five zero gram solid mixture containing
calcium sulfate is dissolved in water and treated with an excess of barium
nitrate resulting in the precipitation of zero point six one six eight grams of
barium sulfate so let's look at the equation that is associated with this so
we've got some calcium sulfate and then remember we are treating this with an
excess of barium nitrate and then that is going to generate a barium sulfate
precipitation and then calcium nitrate that's just going to be spectator ions
and so we have some solid mixture some of it is calcium sulfate some of it
is something else we're not sure and what we want to figure out is what
percentage of that mixture was calcium sulfate and so we're gonna do
gravimetric analysis in order to figure this out and so when you're ready give this a try.
so up top let's put this equation and then let's put our
information so we know that we got zero point six one six eight grams of a
barium sulfate precipitate so we were able to get that precipitate remove it
from solution find the mass and we got that mass of the precipitate and we want
to use that information to figure out first of all what mass of calcium
sulfate had to react in order to generate that much barium sulfate
precipitate so let's do some stoichiometry here first of all whenever
we do stoichiometry we know we don't want mass we need moles because moles
allow us to do store qiyamah trees so zero point six one six eight grams of
barium sulfate times one mole over two hundred thirty three point three eight
grams that the molar mass of barium sulfate that is
going to give us zero point zero zero two six four three moles so that is the
moles contained in the barium sulfate precipitate that we got we measured the
mass for and so now what we also need to understand is that if that's the number
of moles of barium sulfate precipitate that is also equal to the number of
moles of calcium sulfate that reacted because we have a one to one ratio here
for every one calcium sulfate we get one barium sulfate so the moles of barium
sulfate that's equal to the moles of calcium sulfate that reacted so now all
we have to do is convert that into a mass of calcium sulfate so we're gonna
take zero point zero zero two six four three moles of calcium sulfate and
multiply that by 136 point one four grams per mole that is the molar mass of
calcium sulfate and we end up with zero point three five nine eight grams of
calcium sulfate so this gravimetric analysis allowed us to figure out what
mass of calcium sulfate was in the solution and so we just take the zero
point three five nine eight grams of calcium sulfate that were in solution
and divide by zero point four five five zero grams which was the mass of the
initial solid mixture before we put it into solution times 100 and we find out
that seventy nine point zero eight percent of that solid mixture was calcium sulfate.