Molar Mass Lab
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
Needle
Unknown liquid sample (CH3OH)
Ring stand and beaker clamp
Procedure:
1) Prepare 1000 ml beaker by filling with water and heat to boiling on the hot plate …show more content…
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 water at which all the volatile liquid transformed into gas(this is the temperature of the liquid) and atmospheric pressure.
10) When flask completely cooled, wipe outside of flask dry and mass
11) Add more unknown and repeat experiment (if time permits)
12) Rinse flask and fill with water completely
13) Take the temperature to find density
14) Mass flask and water to find mass of water
15) Find volume of Flask
Data/Calculations Mass of the flask and cover | 169.2g | Pressure in mm Hg | 741.2mm Hg | Temperature in vapor (°C/°K) | 98.0 °C/ 371.0°K | Mass flask and Water | 759.3g | Mass Water in Flask | 509.1g | Temperature of Water in flask | 22.0°C | Density of Water | .99780g/mL | Volume of Flask | 591.4mL | Amount of methanol used | 5.0mL | Mass Flask and Methanol Gas | 169.8g | Mass Methanol Gas | .6g | Calculated Molar Mass of Methanol | 30g/mol | Accepted Value for Molar Mass | 32.05g/mol | Percent Error |
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The experiment’s objective is to calculate the experimental value of molar mass of a volatile liquid through the process of heating, and compare the results to the accepted value for the analysis of accuracy. The objective of the experiment was achieved by obtaining 30g/ mol as the molar mass of methanol gas. Possible sources of error that could have affected the results include over heating the gas, which could have allowed air to enter the flask, which would explain why the molar mass was lower than the accepted value. Also, the lid was not a perfect seal for the container and may have allowed the gas to escape and because there was a hole inserted into the top, the air would have enter and affect the results. Lastly, we had a larger percent error due to significant figures. Resolutions to these sources of error could include applying the Dumas method to the experiment, more careful observation of the liquid’s transformation into a gas, and utilizing more accurate equipment in the room for more accurate results.
Materials:
500 ml Erlenmeyer flask 1000 ml beaker Hot plate Aluminum foil
Needle
Unknown liquid sample (CH3OH)
Ring stand and beaker clamp
Procedure:
1) Prepare 1000 ml beaker by filling with water and heat to boiling on the hot plate …show more content…
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 water at which all the volatile liquid transformed into gas(this is the temperature of the liquid) and atmospheric pressure.
10) When flask completely cooled, wipe outside of flask dry and mass
11) Add more unknown and repeat experiment (if time permits)
12) Rinse flask and fill with water completely
13) Take the temperature to find density
14) Mass flask and water to find mass of water
15) Find volume of Flask
Data/Calculations Mass of the flask and cover | 169.2g | Pressure in mm Hg | 741.2mm Hg | Temperature in vapor (°C/°K) | 98.0 °C/ 371.0°K | Mass flask and Water | 759.3g | Mass Water in Flask | 509.1g | Temperature of Water in flask | 22.0°C | Density of Water | .99780g/mL | Volume of Flask | 591.4mL | Amount of methanol used | 5.0mL | Mass Flask and Methanol Gas | 169.8g | Mass Methanol Gas | .6g | Calculated Molar Mass of Methanol | 30g/mol | Accepted Value for Molar Mass | 32.05g/mol | Percent Error |
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The experiment’s objective is to calculate the experimental value of molar mass of a volatile liquid through the process of heating, and compare the results to the accepted value for the analysis of accuracy. The objective of the experiment was achieved by obtaining 30g/ mol as the molar mass of methanol gas. Possible sources of error that could have affected the results include over heating the gas, which could have allowed air to enter the flask, which would explain why the molar mass was lower than the accepted value. Also, the lid was not a perfect seal for the container and may have allowed the gas to escape and because there was a hole inserted into the top, the air would have enter and affect the results. Lastly, we had a larger percent error due to significant figures. Resolutions to these sources of error could include applying the Dumas method to the experiment, more careful observation of the liquid’s transformation into a gas, and utilizing more accurate equipment in the room for more accurate results.