Original subtitles

hi everyone my name is lisa nichols and

today i'm going to show you how to

determine the boiling point of a liquid

using one of these a feel tube

first you'll want to clamp the feel tube

to a ring stand and i tend to clamp it

right at the triangle you also want to

make sure that there's enough oil in the

tube it should completely cover that

triangular area there should be no gaps

next you'll

get your thermometer set up and

if you use a rubber stopper that has a

hole in it with a slit

the thermometer can slip in there really

nicely

and next i tend to

try to position the thermometer almost

correctly

you want to position it so that the

bottom of the thermometer bulb is

roughly halfway maybe a little higher

but that it will sit into the oil

and next i'm going to put a

small

tube onto the thermometer this is called

a

durum tube and you want to make sure

there's no liquid in there yet because

otherwise it's just awkward but you take

your empty tube and you can connect it

with a little small rubber band

and just slip that on

and try to position it

rather high onto the tube when you stick

it into the oil you want to make sure

that that rubber band isn't actually

submerged in the oil or it might pop

next you want to take the liquid that

you want to analyze its boiling point of

and add that to the derm tube fill it up

roughly between a half and two-thirds

full

and then you're going to take a

capillary tube which is open on one end

and sealed on the other end and put it

into the tube with the open end down the

sealed end should be on the top

and then that whole setup is going to go

into the oil

likely you're going to have to adjust

the height again to get it exactly right

you want to make sure that that rubber

band is not actually submerged in the

oil but you want it to get as low as

possible

your sample should definitely be

submerged in in the oil

or surrounded by the is more more

accurate

if you notice the thermometer touching

the glass you want to try to adjust it

so that doesn't happen as well

off to the side you then want to light a

bunsen burner

bring that in and start heating the arm

of the feel tube this is a way to

indirectly heat the sample because

you'll end up creating a current within

the oil the hot oil will rise the cooler

oil will sink and you'll create a

current

that eventually moves energy around and

heats your sample

so keep on gently waving the bunsen

burner on the arm of the feel tube

and eventually you're going to heat your

your sample up

at some point you you might notice

bubbles within the oil

i don't think it happens too much on on

the example that that i have but

sometimes if you do notice bubbles in

the oil what that is is just from um

past students where the rubber band has

broken and the sample has spilled out

into the oil and so you're really just

boiling that

uh material that organic material inside

the oil

in the interest of time i'm going to

speed it up a little

and let's zoom in on the tube and see

what's happening there

so eventually as you heat it you're

going to start getting bubbles coming

out of the capillary tube

and what you want to do is keep on

heating it gently until you get a

vigorous stream of bubbles

so vigorous that it's hard to

distinguish between each individual

bubble

so this would definitely be good enough

what you then do is you want to take off

the heat

so you turn off your bunsen burner and

then you just let the whole system cool

down at this point you're actually a

higher temperature than the boiling

point you've overshot it

but you want to let the whole

the oil cool down and the sample cool

down

and what we're trying what you're

looking for is you want to get to the

point where those bubbles eventually

slow and completely stop and you just

get that moment where the first little

bit of liquid pulls into that capillary

tube

we'll see it here in in a while

sometimes what will happen is that

you'll have actually heated it too

rapidly and

you'll get all of the liquid to

evaporate completely

you don't want that

if that happens then you just have to

repeat the whole thing and try to go a

little more slowly the the second time

around

so this is actually a sped up video it's

probably about three times the speed it

does take quite a while for the bubbles

to stop but eventually they will slow

and notice also our liquid level has

been reduced as well because a lot has

evaporated away

or boiled away

and

eventually though you should have some

liquid left

and you should start seeing you know

bubbles becoming less frequent

they get much more slow

one every couple seconds or so and what

we're looking for

is that first moment where the bubbles

are done and the liquid draws into the

capillary tube

and here they've stopped

that moment do you see it it's just

starting but i would say that that would

be the boiling point

so you look up on your thermometer

and you record this temperature as your

boiling point

now it's a little bit past but you see

how the liquid draws into the capillary

tube

so it keeps on traveling

but we wanted we wanted to have written

the

the temperature down on the thermometer

a little while ago

and that's the way that you can measure

the boiling point using a feel tube