Question

experiment to determine the boiling point of a liquid

Answer 1

DETERMINATION OF BOILING POINT OF A LIQUID .                                                                                                                                                                        Introduction:

The boiling point of a compound is the temperature at which it changes from a liquid to a gas.  This is a physical property often used to identify substances or to check the purity of the compound.  

It is difficult, though, to find a boiling point.  Usually, chemists can only obtain a boiling range of a 2 - 3oC accuracy.  This is usually  sufficient for most uses of the boiling point.

Purpose:

The purpose of this experiment is to determine the boiling points of various organic compounds and to use these to identify unknowns.

Equipment / Materials:

hot plate closed end capillary tube

thermometer liquid organic compounds

250 mL beaker small test tube

Safety:

* Always wear safety glasses in the lab.

* Capillary tubes break very easily, handle them with caution.

* Be careful with the thermometer.  Mercury is very toxic.

Procedure:

1. Place a few milliliters of a known liquid organic compound in a small test tube.

2. Into the test tube, place the capillary tube with closed end upward.

3. Clamp the test tube to a ring stand and immerse a thermometer in the test tube.  Be

sure to clamp the thermometer to the ring stand as well.

4. Fill a 250 mL beaker 3/4 full with water and place on the hot plate.  Carefully lower

lower the test tube and thermometer combination into the beaker of water so that the

test tube is immersed half way in the water.

5. Begin to heat the hot plate/water slowly.  As the liquid approaches its boiling point, a

few bubbles will be observed flowing out of the end of the capillary tube.  When a  

steady steam of bubbles are observed, turn off the hot plate and allow the contents of

the test tube to cool.

6. As the contents of the test tube cools, observe the capillary tube carefully.  When

the liquid begins to flow into the capillary tube, record the temperature of the liquid

as its boiling point temperature.

7. Obtain an unknown liquid and repeat steps 1-6.

Substance Boiling point (C)

acetone 56-57

methanol 65

ethanol 78-79

propanol 97-98

                                                                                                                                                                                                                                                                      DETERMINATION OF BOILING POINTS

Data Table:

Practice Compounds:

compound   boiling range  

-             oC

compound   boiling range  

-             oC

Unknown:

compound  

Unknown # ___________ boiling range  

-             oC

identity of substance