Why is the volumetric pipette the most precise
How to Use a Volumetric Pipette
here we have three ways of measuring out
25 milliliters of liquid the 25
milliliter beaker the 25 million
cylinder and the 25 milliliter
volumetric pipet the difference between
these is the beaker will measure 25
milliliters the graduated cylinder will
measure 2 25.0 milliliters and the
volumetric pipette will measure 2 25.00
milliliters so the difference here is
the beaker only gives us two significant
figures the graduated cylinder gives us
three significant figures and the
volumetric pipette will give us four
significant figures so to get the most
accurate and precise reading possible
we'll be learning how to use the
volumetric pipette correctly today the
first thing when getting your volumetric
pipette is to clean it with water
because you do not know what
contaminants are on the inside when you
are using your volumetric pipette always
make sure to have one hand secure on the
volumetric pipette and the other hand
secure on the bulb do not assume that
the bulb is going to be holding the
volumetric pipette these are only
supposed to be gently fits in with one
another they will not hold if you just
try holding the biometric pipette with
only the bulb this bottom part will drop
out and it will break so please make
sure that you always have one hand
secure on the pipette itself so when
you're cleaning this out the first thing
you want to do is just squeeze the bulb
and then suck up some water and you only
have to get about half filled here
and once you're satisfied with that you
can just hold it over a waste beaker and
then just swirl it around to make sure
that the water contacts all the insides
and then just let it slowly drain out
and keep spinning it just to make sure
that all the inside surfaces have been
thoroughly washed and once you're done
with that just let the water drain out
and just let it do it naturally and you
may do this one to three times however
many times it takes you to be satisfied
that the inside is actually clean this
particular one is actually pretty nice
and clean here so we don't need to do
much more with that all right you may
notice that there's a little liquid it's
okay to blow this stuff out now because
we don't want to give this diluting our
next sample now after you've rinsed your
pipette with water you also want to
rinse it with the solution that you're
going to be using to avoid any dilution
of the solution from residual water left
in the pipette so you only have to again
fill this up about halfway
so right there is about that we want to
try minimizing the waste that we
actually have and then at this point
again this is going to be over your
waste speaker just swirl this around so
this way it kind of coats the interior
surfaces and any water that was in there
gets rinsed away and once you're happy
with that just let it drain into your
waste container
now once all that is done we're ready to
get our solution alright now that we've
rinsed it we're ready to fill it up and
what we notice is that there is a line
right about here and this is the line
that we want to fill up to so we want
the bottom of the meniscus to match up
to where this line actually is so again
making sure you have one hand secured on
your pipettes press out your bulb and
then start sucking your liquid this may
take two or three times depending upon
you know how successful you are so that
time I didn't get a quite filled so
again I just again hold it over here
with my index finger and then I just
press the bulb again and then suck up
some more liquid
so you'll notice that right here is
where my line actually is and what we
want to do is get it from up here down
to my line so you simply just hold this
over your waste container and from your
finger up here just slightly release it
not all the way but you just want it
loose enough so then some air can get in
and your liquid starts draining down and
you just let it drip down until you're
able to see where it matches up so the
meniscus is matching up with the line
right now as you can see right there the
line and the meniscus are all lined up
so now we simply just hold it over our
vessel and just let it drain and this
may take about a minute for it to fully
drain here
okay now when it's fully drained you'll
notice that there's a little bit of
liquid in there now what's actually
going to happen is is I'm standing here
you'll probably start noticing a little
bit of a drop forming on the outside
that's because the liquid that's
actually like adhering to the outside of
the glass is actually draining down here
and is actually going to start putting
this liquid out so you want to wait
about thirty seconds for that additional
liquid to come out and actually here you
can see the drop which is starting to
emerge so obviously you won't always
have this over your container not in
front of the camera but then just let it
drip out and then when that final drop
actually comes just touch it to the side
of your container and just let it fall
in all right now at this point you'll
notice that there's still a little bit
of liquid left in there we don't want to
go and blow that out even though you're
gonna be very very tempted to the reason
is that these pipettes are designed to
deliver me and that they're designed to
leave that little bit of liquid left in
there and not have it being blown out so
even though it's very tempting please
make sure that you do not blow that out
and put it into there because right now
this contains 25.00 milliliters of
liquid if you add that little bit extra
it's gonna be over and we simply just
don't know how much it will be by so
then at the end of the day when you are
done with this make sure that you rinse
it out with water and that's the same
procedure that we started with so again
you will just go there suck up the DI
water make sure you hold it over your
waste container and spin it around a
little bit and then just let it drain so
this way it washes out and as nice and
clean for the next person okay and that
is how we use our volumetric pipettes
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