Wednesday, July 1, 2009

Lab #2: Distillation

Today's lab was about distillation. We split up into our element groups and then we split into two groups. The other half of my group did the simple distillation of an water and ethanol mixture.

Simple distillation is used when the two liquids have a boiling point difference of about 50 degrees Celsius. Simple distillation occurs when "all hot vapors produced are immediately channeled into a condenser which cools and condenses the vapors." My group got to do fractional distillation which is the "separation of a mixture into its component parts, or fractions." It is used when the liquids have closer boiling points. The difference is though both setups are the same, with an round bottom flask, a variac under that, a distillation head, a thermistor, a condenser, water tubing, an adapter, a drop counter, a funnel, and a graduated cylinder, fractional distillation has glass wool put in its distillation head. The glass wool gives more surface area, which makes the lower boiling-point liquid time to re-evaporate and go through the whole column, while the faster boiling-point liquid are condensed on the glass wool. We used the MicroLab program once again but this time used a drop counter to find out the number of drops of the distilled solution versus temperature.

First, all of us had to assemble the distillation apparatus, which took us some time because we had to make sure we weren't missing a part. We clamped all the glass together, stuck our glass wool into the distillation head with a spatula, and the thermistor was also inserted into the distillation head. We attached a tube to the water source, and we attached another tube to the condenser to get rid of the water. We got a solution of ethanol and water, poured it on the round bottom flask, added a magnetic stir bar, and clamped it to the fractionating column. Then, we started the variac and watched the temperature climb to about 90 degrees, after putting some insulation (aluminum foil) around flask to the beginning of the condenser.

We waited patiently, I would say about an hour, until our drop counter started counting drops of ethanol. My group's patience finally paid off! We got about 600 drops of distilled ethanol, but we had to stop because we had to clean up. But while we were waiting, Professor Avila took another group's distilled ethanol. He lit it on fire and said that it would be pure if the flame didn't have any traces of yellow. Because of our time constraints, the flame had traces of yellow, but it was mostly blue. After lunch, we had a little discussion on distillation and how temperature and pressure affect it.

1 comment:

Don Gosney said...


An interesting lab experiment. I'm afraid that around here even after 600 drops of ethanol you wouldn’t have any to test. Someone would have tried to drink it to get their buzz on.

Post a Comment