LAB EXERCISE 10: MELTING POINT AND BOILING POINT DETERMINATION

CHEMISTRY I - LABORATORY EXERCISE MANUAL

LABORATORY EXERCISE 10: Melting Point and Boiling Point Determination

This is a traditional lab. You'll simply follow the step-by-step procedure, keeping records of your measurements and observations. Each student will write their own lab report, which should include the following:

Name:

Names of lab partners:

Date of Experiment:

Date Report Submitted

TITLE:

Purpose: A brief statement about what the experiment is designed to determine or demonstrate about chemistry

Procedure: Brief summary

Data Tables:

Observations:

Conclusions: What did you learn from the experiment? Should be based on observations made during the experiment.

Evaluation of laboratory exercise type:

On a separate page, each student should write a brief comment regarding

1) which lab method you prefer (inquiry-method, i.e. problem-solving oriented, or traditional lab. like this one.

2) group size (individual labs or small-group labs)

3) report writing - individual or small group

4) Any negative aspects about chem lab & how we can improve them

5) any other comments

We expect an evaluation from everyone. If you prefer not to put your name on this evaluation, that's Ok.

Lab Instructions:

Objectives:

1. To determine the boiling point of a liquid, and
2. To determine the melting point of a solid.

Materials Used:

Matches
Isopropyl (Rubbing) Alcohol
1-2 small rubber bands
Thermometer
Powdered Acetamide beaker
2 closed-end capillary tubes (melting point tubes)
10-12 mm diameter test tube
Heat source

Discussion and Review:

In this experiment we will examine additional physical properties of liquids and solids. Two of the more important physical properties of pure substances are the boiling point and the melting point.

The boiling point of a liquid is the temperature at which that liquid is converted to a gaseous state. Boiling point is formally defined as the temperature at which the vapor pressure of the liquid becomes equal to the pressure at the surface of the liquid. The boiling point of.a liquid can change if the pressure at the liquid's surface changes. Since pure substances have a distinct boiling point, boiling points are sometimes used to determine the purity of substances.

The melting point is the temperature at which a solid is converted to liquid. This is an important property of solids. The melting point of solids, like the boiling point of liquids, is often used for the identification of substances.

Boiling points and melting points are recorded in the Handbook of Chemistry and Physics, and can be found in the sections titled "Physical Constants of Organic Compounds" and "Physical Constants of Inorganic Compounds".

PROCEDURES:

I. Boiling Point

1. Make a test tube assembly by using the following directions and illustration.

a. Place about 1 mL of Isopropyl alcohol in a 10-12 mm diameter test tube.

b. Using a small rubber band, attach a thermometer to the outside of the test tube. The thermometer bulb should be even with the test tube's bottom.

c. Insert an inverted closed end capillary tube into the test tube.

2. Make a water bath assembly by using the following directions and illustration.

a. Half fill a 100 mL or larger beaker with warm tap water. [Note: a water bath is used if the boiling point of the material is expected to be less than the boiling point of water; otherwise, an oil bath is needed.]

b. Place the above test tube assembly in the water bath so that the surface level of the alcohol in the test tube is beneath the surface level of the water bath.

c. Place the beaker on the wire stand and, stirring frequently to insure even heating, carefully heat the water bath with your heat source until the water bath boils and a rapid stream of bubbles continuously emerges from the capillary tube. [Note: if an oil bath is used, the oil does not boil; the stream of bubbles from the capillary tube is the sole indicator that the liquid in the pipet or test tube is boiling.]

d. Remove the heat source and begin observing the stream of bubbles.

e. When the last bubble emerges from the capillary tube, record the temperature.

3. Reheat the water bath and repeat the cooling process two more times. Record the temperature reading after each trial, and average all three trials.

4. The published boiling point of isopropyl alcohol is 82.4 ^oC.

5. Calculate the error between the observed boiling point and the published value of the boiling point.

II. Melting Point

1. a. Push the open end of a capillary tube into the powdered acetamide.

b. Move the powder to the closed end of the capillary tube by tapping it on the table. Repeat until the the powdered acetamide occupies 1-2 mm of the capillary tube end.

c. With rubber bands, attach the capillary tube to a thermometer and align the bulb of the thermometer with the closed end of the capillary tube.

d. Make a water bath as before by half filling a 100 mL beaker with warm tap water.

e. Place the thermometer/capillary tube assembly in the water bath so that the surface level of the powdered acetamide is beneath the surface level of the water bath.

f. Place the beaker on the burner stand and, stirring frequently to insure even heating, carefully heat the water bath with your heat source.

g. Note the temperature at which the acetamide melts. Remove heat source.

h. Let the acetamide cool and recrystallize. Repeat the procedure two more times and average the results.

i. The published melting of acetamide is 81^oC. Compare your experimental result with the accepted (published) value.

j. Calculate the percent error.

Clean-up:

Dispose of the used capillary tubes by putting them in your trash can. If any isopropyl alcohol is left in your test tube, you may pour it down the drain with water.

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