Transcript Template
Experimental Procedure
Lab 402
A. Preparing the Sample
Prepare a boiling water bath on a for PARTA.3
1.Prepare the flask for sample
Determine the mass (0.001 g) of the
dry
.
Clean a 125-mL Erlenmeyer flask and dry it either in a drying oven or by allowing it to air dry. Do not wipe it dry or heat it over a direct flame. Cover the dry flask with a small piece of aluminium foil and secure it with a rubber band.
flask, aluminum foil, and rubber band.
2. Prepare a boiling water bath
temperature of the water bath.
.
Half-fill a 500-mL beaker with water. Add one or two boiling chips to the water. Use a hot plate as a heat source. Secure a digital thermometer to measure the
3. Place the sample in the flask
times.
.
Record the number of the unknown liquid on the Report Sheet. Transfer about 5 mL of the unknown liquid into the flask; again cover the flask with aluminum foil and secure the foil with a rubber band. You do not need to conduct a mass measurement. With a pin, pierce the aluminium foil several
B. Vaporize the Sample
1. Place the flask/sample in the bath
the water level high on the neck of the flask (Figure 12.2).
.
Lower the flask/sample into the bath and secure it with a utility clamp. Be certain that neither the flask nor the clamp touches the beaker wall. Adjust
2. Heat the sample to the temperature of boiling water
.
Gently heat water until it reaches a gentle boil.
(Caution: Most unknowns are flammable) When the liquid in the flask and/or the vapors escaping from the holes in the aluminum foil are no longer visible, continue heating for another 5 minutes. Read and record the temperature of the boiling water.
The movable arm hood is a local exhaust system that can be ventilated small contaminated air to protect both user and area safety from harmful material.
3. Measure the mass of the flask/sample
foil, rubber band, and the remaining vapor.
.
Remove the flask and allow it to cool to room temperature. Sometimes the remaining vapor in the flask condenses; that’s okay. Dry the outside of the flask and determine the mass (0.001 g, use the same balance!) of the flask, aluminum
4. do it again and again
Repeat the experiment for Trial 2 and 3.
You only need to transfer another 5 mL of liquid to the flask (i.e., begin with PART A.2) and repeat PARTs B.1-B.3.
C. Determine the Pressure of the Vapor Volume and
1. Measure the volume of the flask
Record the total volume.
.
Fill the empty 125 mL Erlenmeyer flask to the brim with water. Measure the volume (0.1 mL) of the flask by transferring the water to a 50- or 100-mL graduated cylinder.
2. Record the pressure of the vapor in the flask.
atmosphere pressure in atmospheres to correct number of significant figures.
Find the barometer in the laboratory. Read and Record the
D. Calculations
1. Molar mass from data
.
unknown for each of the three trials.
Calculate the molar mass of your
2. Determine the standard deviation and the relative standard deviation (%RSD).
B and calculate the standard deviation and the % RSD for the molar mass of your unknown from your three trials.
Refer to Appendix
3. Obtain group data.
Obtain the values of molar mass for the same unknown from other chemists. Calculate the standard deviation and the % RSD for the molar mass of the unknown.
The next steps
A number of techniques can be used to determine the molar mass of a volatile liquid; the most common (if the instrument is available) is mass spectrometry. Describe how your sample’s molar mass would be determined using mass spectrometry.
Search the Internet for other procedure that can be used to measure the molar mass of volatile substances.
Unknown Liquids
Methanol Absolute Ethanol Acetone 2-propanol n-hexane Cyclohexane 1-pentaene Cis-2-pentene 2-butanone N-pentane Cyclohexene 1-hexene Ethyl acetate