When using the Dumas Method....   The student filled their 400 mL beaker with 250 mL of tap water and added 2 boiling stones.  They then sat their beaker on the hot plate and clamped it in place using a metal ring attached to a ring stand. The student began heating the beaker. The student obtained a 250 mL Erlenmeyer flask from the drying rack.  It looked clean but had a few water droplets inside.   The student cut out a 3 inch by 3 inch piece of aluminum foil and found a rubber band. The student determine the mass of the Erlenmeyer flask + piece of foil + rubberband.  The mass was 68.780 g. The student used a 10 mL graduated cylinder to measure out 4.5 mL of unknown liquid.  They added their unknown liquid to the 250 mL Erlenmeyer flask.   The student covered the Erlenmeyer with aluminum foil and rubber band.   Using a paper clip, the student poked 3 holes in the top of their aluminum foil The student then clamped their flask in the water bath, that hadn't started boiling yet.   When the liquid was completely evaporated, the student removed the Erlenmeyer flask from the water bath (which still wasn't boiling), quickly dried the flask and then weighed it.  The weight of the flask was 69.092 g.   The student then wrote down the pressure of the lab from the barometer (0.998 atm).  The student then hastily wrote down that the water bath had a temperature of 100 °C and the volume of their Erlenmeyer to be 250 mL.    Identify 3 sources of error in the above experiment. How would each of these errors effect their calculated molar mass and comment on each source of error including the results it would give. Based on the data the student collected, calculate the molar mass of their unknown gas.

When using the Dumas Method....

• The student filled their 400 mL beaker with 250 mL of tap water and added 2 boiling stones.  They then sat their beaker on the hot plate and clamped it in place using a metal ring attached to a ring stand.
• The student began heating the beaker.
• The student obtained a 250 mL Erlenmeyer flask from the drying rack.  It looked clean but had a few water droplets inside.  
• The student cut out a 3 inch by 3 inch piece of aluminum foil and found a rubber band.
• The student determine the mass of the Erlenmeyer flask + piece of foil + rubberband.  The mass was 68.780 g.
• The student used a 10 mL graduated cylinder to measure out 4.5 mL of unknown liquid.  They added their unknown liquid to the 250 mL Erlenmeyer flask.  
• The student covered the Erlenmeyer with aluminum foil and rubber band.  
• Using a paper clip, the student poked 3 holes in the top of their aluminum foil
• The student then clamped their flask in the water bath, that hadn't started boiling yet.  
• When the liquid was completely evaporated, the student removed the Erlenmeyer flask from the water bath (which still wasn't boiling), quickly dried the flask and then weighed it.  The weight of the flask was 69.092 g.  
• The student then wrote down the pressure of the lab from the barometer (0.998 atm).  The student then hastily wrote down that the water bath had a temperature of 100 °C and the volume of their Erlenmeyer to be 250 mL. 

Identify 3 sources of error in the above experiment. How would each of these errors effect their calculated molar mass and comment on each source of error including the results it would give. Based on the data the student collected, calculate the molar mass of their unknown gas.