The molar mass of a volatile liquid(one which vaporizes easily) can be determined by a the 'Dumas Method.' In this process a small amount of the liquid (a few drops) is placed in a clean flask. The mouth of the flask is civered with a piece of foil that has a small hole (pin hole) in it. The flask is heated in a boiling water bath until the liquid vaporizes completedly.
To determine the molar mass of a volatile liquid using the Dumas method, you will need the following materials and equipment:
1. Clean flask
2. Volatile liquid
3. Foil
4. Pin (to create a small hole in the foil)
5. Boiling water bath
Here is a step-by-step explanation of how to use the Dumas method:
1. Clean the flask thoroughly to ensure there are no impurities or residues that could affect the measurement.
2. Measure a few drops of the volatile liquid and carefully add them to the clean flask.
3. Cover the mouth of the flask with a piece of foil, making sure it is tightly secured. Use a pin to create a small hole in the foil, which will allow vapor to escape during the experiment.
4. Prepare a boiling water bath by filling a container with water and heating it to its boiling point. Make sure the flask can be submerged in the boiling water without any water entering the flask.
5. Carefully place the flask in the boiling water bath, ensuring that it remains upright and the liquid inside starts to boil.
6. Wait until all the liquid has vaporized completely. This is indicated by a steady stream of vapor escaping through the pinhole in the foil.
7. Once the liquid has vaporized, remove the flask from the boiling water bath and let it cool down to room temperature. It is important to make sure that no condensed liquid re-enters the flask during this cooling period.
8. Weigh the clean, dry flask using an analytical balance with high precision. Note down the mass of the flask.
9. Using the ideal gas law equation, PV = nRT, where P represents pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature, you can rearrange the equation to calculate the number of moles (n) of the volatile liquid.
10. Once you have calculated the number of moles, divide the mass of the volatile liquid by the number of moles to obtain its molar mass. The units of molar mass are grams per mole (g/mol).
By following these steps, you can use the Dumas method to determine the molar mass of a volatile liquid.