heres what i'm working on right now.. stupid chemistry lab
Andrew Lee
Albert Oh
Section 6
Molar Mass of a Volatile Liquid
Objective
The objective of this lab was to measure the volume and mass of an unknown liquid and figure out its molar mass.
Materials and Equipment
600 mL beaker
125 mL Erlenmeyer flask
One-holed rubber stopper with a plastic tube
250 mL graduated cylinder
Hot plate
Water
Unknown volatile liquid
Ring stand
Utility clamp
Thermometer
Electronic scale
Procedure
The 600mL beaker was filled with 400mL of water and place on the hotplate to boil. Meanwhile, a 125mL Erlenmeyer flask was weighed, filled with 3-4mL of the unknown liquid and plugged with the rubber stopper. The flask was clamed to the utility clamp and was slowly lowered into the beaker of boiling water using the ring stand. After all the liquid in the flask vaporized, the flask was removed from the boiling water and set to cool. The temperature of the boiling water was taken. The flask was cooled, dried, and then weighed again. The flask was emptied and the steps were repeated. Then, the stopper was pulled out. The flask was filled with water, plugged again, and dried. After that, the volume of the water was measured by pouring it in a graduated cylinder.
Data and Observations
Unknown used Liquid A
Mass of flask, stopper, and tube 87.45g
Mass of flask, stopper, tube, and condensed vapor 87.89g 87.94g
Temperature of boiling water 100.3°C
Barometric pressure 751 mmHg
Volume of flask 147mL
Calculations
Mass of condensed vapor: 87.94g – 87.89g = .05g
Barometric Pressure in atm: 751mmHg * (1atm / 760mmHg) = .988atm
Temperature to Kelvin: 100.3°C + 273 = 373.3K
Volume to liters: 147mL * (1L / 1000mL) = .147L
Molar mass of unknown: mm = (gRT) / (PV) = (.05)(.0821)(373.3) / (.988)(.147)
= .23 g/mol
Results
The molar mass of the unknown was
Questions
What effect would each have on the calculated molar mass? Would the calculated molar mass be too high or too low?
1. The flask was not fully dry when it was weighed after cooling. Too high
2. The flask was kept in the boiling water for too long. Too low
3. The flask was removed from the boiling water too soon. Too high
4. Water was inside the flask before the addition of unknown liquid. Too high