Molar Mass

Topics: Gas, Ideal gas law, Pressure Pages: 3 (709 words) Published: January 30, 2011
Molar Mass of a Volatile Liquid
There are several ways to find the molar mass of a substance. One way, if the substance is a gas, is to use the Ideal Gas Equation to find molar mass. The standard equation reads PV=nRT where “n” is the number of moles present, “P” is the pressure (which is obtained by reading the barometric pressure of the room with the class barometer), “V” is the volume of the gas, “R” is the universal constant, and “T” is the temperature of the gas. The experiment’s objective is to calculate the experimental value of molar mass of a volatile liquid through the process of heating (to form a gas, and thus use the ideal gas law to calculate the molar mass), and compare the results to the accepted value for the analysis of accuracy. This can be achieved by substituting the mass of the substance over the molar mass of the substance for “n”: m/M=n. The liquid heated to a gas is methanol, which has an accepted value for molar mass of 32.05g/mol. Materials:

500 ml Erlenmeyer flask
1000 ml beaker
Hot plate
Aluminum foil
Unknown liquid sample (CH3OH)
Ring stand and beaker clamp

1) Prepare 1000 ml beaker by filling with water and heat to boiling on the hot plate 2) Clean and dry the 500 ml Erlenmeyer flask
3) Cut a square of aluminum to fit the Erlenmeyer flask as a lid 4) Mass the empty flask and cap
5) Add 5 ml of unknown liquid (CH3OH) and (if desired) boiling stones to flask. Put on lid and poke small hole in lid (this helps for the pressure of the gas to be equivalent to the pressure of its surroundings, in which the pressure obtained by barometer will be utilized in the Ideal Gas Law Equation). Mass the liquid. 6) Place flask filled with volatile liquid in boiling water, clamping the flask to the stand. 7) When all the liquid unknown (CH3OH) has vaporized, let it sit one minute in the boiling water, then remove the flask from the heating source 8) Let the flask cool

9) Measure the temperature of boiling...
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