If you have LOTS of If you have LOTS of sample, you can sample, you can

determine the boiling determine the boiling point by distilling the point by distilling the

sample.sample.This provides the b.p. This provides the b.p. AND it cleans up the AND it cleans up the

sample.sample.However, if you have However, if you have

only a few milliliters (or only a few milliliters (or even less), you must use even less), you must use

other methods.other methods.

Determining boiling points Determining boiling points with small samples.with small samples.

The MicroThe Micro MethodMethod

Determining boiling points Determining boiling points with small samples.with small samples.

andand The Semi- The Semi- micro Methodmicro Method

Determining boiling points Determining boiling points with small sampleswith small samples.

The first segment is taking boiling The first segment is taking boiling points by the “micro” method.points by the “micro” method.

Several Several dropsdrops of sample will of sample will

be required for this method.be required for this method.

Place several drops in a 3 inch test tube; and Place several drops in a 3 inch test tube; and invert a capillary tube into the sample.invert a capillary tube into the sample.

Fasten the sample along side a thermometer bulbFasten the sample along side a thermometer bulb..

Clamp the assembly in the oil bath.Clamp the assembly in the oil bath.

Take care that the rubber ring is not Take care that the rubber ring is not touched by the oiltouched by the oil.

HeatHeat and and stirstir until a rapid stream of until a rapid stream of bubbles is coming from the tubebubbles is coming from the tube.

You are You are ABOVEABOVE the boiling point! the boiling point!

Remove the burner, Remove the burner, BUT KEEP STIRRING!!!BUT KEEP STIRRING!!!

Continue to stirContinue to stir,, and watch!!and watch!! As the sample cools, As the sample cools,

the stream of bubbles slows down.the stream of bubbles slows down.

Continue to stir!Continue to stir! The bubbles The bubbles come come slowerslower and and s l o w e rs l o w e r

. . .and even . . .and even s – l – o – w – e - rs – l – o – w – e - r

Finally one bubble doesn’t make it out! Finally one bubble doesn’t make it out! The The liquid runs back up the tube!liquid runs back up the tube!

Did you see it ???Did you see it ???

Look at your thermometer!Look at your thermometer!

THIS IS THE BOILING POINT!!THIS IS THE BOILING POINT!!

Use a different test tube for Use a different test tube for each sampleeach sample.

• When you have finished, When you have finished, CLEANCLEAN and and DRYDRY the 3-inch the 3-inch test tubes. Keep them in your test tubes. Keep them in your lab drawer. They will be used lab drawer. They will be used again next week in Sodium again next week in Sodium FusionsFusions..

This segment is taking This segment is taking boiling points by the boiling points by the “semi-micro” method“semi-micro” method

A A milliliter or twomilliliter or two of sample will of sample will be used in this method.be used in this method.

Start with a good ring standStart with a good ring stand..Tighten the rod!!Tighten the rod!!

Add an iron ring about 6 – 7 inches up Add an iron ring about 6 – 7 inches up from the base.from the base.

You need a wire gauze with a You need a wire gauze with a ceramic center.ceramic center.

There should be a pencil-size hole in theThere should be a pencil-size hole in the

ceramic center.ceramic center.

Position the wire gauze on the Position the wire gauze on the iron ring.iron ring.

Clamp a medium-size test tube on Clamp a medium-size test tube on the hole; -- no air space!the hole; -- no air space!

Add a milliliter or two of the sample . . .Add a milliliter or two of the sample . . .

and one boiling stone.and one boiling stone.

Clamp the thermometer assembly . . .Clamp the thermometer assembly . . .

. . . with its bulb . . . with its bulb centeredcentered an inch or two an inch or two above the liquid sample.above the liquid sample.

Light the burner and adjust it to a Light the burner and adjust it to a smallsmall flame . flame .

Play a Play a small small flame directly onto the hole in flame directly onto the hole in the wire gauze.the wire gauze.

Bring the sample to a gentle boil.Bring the sample to a gentle boil.

Watch for steady drops falling off the Watch for steady drops falling off the thermometer bulb.thermometer bulb.

When the temperature becomes stable . . . no When the temperature becomes stable . . . no longer rising . . .longer rising . . .

Record the boiling point!Record the boiling point!

Your Laboratory Report Form is due the day on which you perform the Boiling Points Experiment. Be prepared to turn it in.

bp-rept.doc LABORATORY REPORT FORM DETERMINATION OF BOILING POINTS NAME: Section: Date:_____________________ NAME(S) of your Lab Partner(s)________________________________________________________

Name of Compound

Structure

Micro Method

Semimicro Method

Literature Value

isopropyl alcohol, or t-Butyl alcohol

n-propyl alcohol, or sec-butyl alcohol

n-butyl alcohol

isoamyl alcohol, or n-amyl alcohol

cyclohexanol, or cyclohexanone

unknown ( )

unknown ( )

unknown ( )

Record your comments regarding which of the two methods gave you the better results. (You will be using one or both methods when you are trying to identify your unknowns.)