Distillation

The proper distillation rate for experiment 8 was:

1-2 drops per second

A distillation flask should be filled to:

1/2-2/3 of its max volume

In this experiment, what could cause an NMR sample to have a much higher acetone content than expected (compared to the GC of the same sample)?

If the NMR tube was cleaned with acetone that was not removed, then there would be a relatively large amount of acetone in the NMR compared to the GC.

Why is it necessary to carry out a slow, even distillation in order to achieve good separation between components in a mixture?

If the distillation flask is superheated, larger quantities of the higher-boiling components distill in the early fractions. Also, the added heat and excess quantities of vapors prevent equilibrium between liquid and gas in the distillation head. A slow, even distillation is necessary to achieve a good separation because only under these conditions will vapor and liquid be in equilibrium with one another in the distillation apparatus. If a mixture is heated too rapidly the rising vapor will have a chance of being carried over to the receiver without condensing. Thus, more higher-boiling material will be found mixed in with the lower boiling material

What could cause an NMR sample to have a much lower acetone content than expected?

If the sample were left uncapped for a long time after a sample was taken out for GC, then the acetone would evaporate faster than the ethyl acetate, leaving a lower amount of acetone present in NMR.

If a compound boils at 100°C at 760 torr, its boiling point at 725 torr will be:

Lower than 100°C

In a fractioning column:

Successive simple distillations take place on the packing material

When a careful distillation is performed on a mixture of liquids with widely different boiling points, the head temperature rises and plateaus, then drops before rising again during the distillation. Explain what is happening during each of these phases.

The head temperature rises as the vapors of lower-boiling compound fill the distillation head. The temperature drops because the lower-boiling compound finishes distilling before vapors of the higher-boiling compound can fill the distillation head, which then cause the head temperature to rise. Phase one: initial rise - vapors of low boiling material reaching thermometer. Phase two: plateau - vapors of low boiling material in thermal equilibrium with condensate on thermometer bulb. Phase three: drop - too little vapor of lower boiling component is reaching thermometer to remain in equilibrium with condensate; higher boiling vapors not yet reaching thermometer. Phase four: higher boiling vapors reaching thermometer.

Why does a rapid distillation that floods the fractionating column lead to poor separation of components?

The vapor-liquid equilibrium is not established, leading to decreased efficiency (fewer theoretical plates).

In fractional distillation the fractioning column is placed:

between the distillation flask and the y-adapter

The boiling point of a liquid is defined as the temperature at which

its vapor pressure equals atmospheric pressure

What is not a valid use for gas chromatography?

purifying a large amount of compounds

When performing a distillation, the boiling point is measured:

At the junction of the y adapter and the condenser

In gas chromatography, the retention time for a compound is defined as the time it takes:

a compound to pass through the column and reach the detector