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 plateclosed end capillary tube
thermometerliquid organic compounds
250 mL beakersmall test tube
*Always wear safety glasses in the lab.
*Capillary tubes break very easily, handle them with caution. *Be careful with the thermometer.
1.Place a few milliliters of a known liquid organic compound in a small test tube.
2.Place the capillary tube into the test tube with the closed end upward.
3.Clamp the test tube to a ring stand, and immerse a thermometer in the test tube.
4.Fill a 250 mL beaker 3/4 full with water, and place on the hot plate. Carefully 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 stream 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.