The boiling point of a liquid is often referred to as a temperature at which the liquid turns into a vapor spontaneously anywhere in the liquid. This definition while handy and for the most part accurate, is a generality. This is because most of the time the boiling point of a liquid is determined at the same pressure, usually 1 atmosphere (760 mm Hg or 101.325 kPa)
Strictly speaking, the boiling point of a liquid is the temperature at which the vapor pressure of the liquid is equal to the pressure above the liquid. This point is usually signaled by the appearance of the characteristic bubbles seen anywhere in the liquid.
In this experiment, the boiling point of various liquids will be determined.
One of the following liquids:
Acetone small beaker (250 mL)
1-propanol medium test tube
2-propanol closed end capillary tube
hot plate (if available) or
bunsen burner, ring stand,
iron ring, wire gauze buret clamp
CAUTION: All of the liquids used in this experiment are flammable. Keep away from open flames.
1. Place the capillary tube into the test tube with the sealed end up.
2. Place 3-4 mL of the test liquid in the test tube.
3. Strap the test tube to the thermometer so that the bottom of the test tube is even with the bottom of the thermometer.
4. Clamp the test tube and thermometer assembly to the ring stand.
5. Fill the small beaker about ½ full with tap water. Arrange the test tube/thermometer assembly so that the test tube and thermometer are in the water bath but the water level does not go above the top of the test tube. See Diagram #2.
6. Heat the water bath, with constant stirring, until a steady stream of bubbles is seen issuing from the open end of the capillary tube. When the bubbles are first noticed, not the temperature and take this to be the approximate boiling point.
7. Stop heating the water bath.
8. Stir the water bath constantly until the stream of bubbles just stops. Note the temperature. This is the boiling point.
9. Compare the boiling point you obtained with the accepted boiling point in the Handbook of Chemistry and Physics.
10. Calculate the percent error using the following formula:
% error = observed temperature – theoretical temperature
1. The boiling points for all the liquids in this lab are less than 100ºC. How do you know this before ever beginning the lab?
2. How can the boiling point of a liquid with a boiling point greater than 100ºC be determined?
3. What are some sources of error?