Fractional Distillation (Exp 7)

Select the mechanism by which a sample travels through a gas chromatograph.

The sample is carried by an inert gas mobile phase such as helium.

Select the statement that is NOT a likely consequence of placing the thermometer bulb inside the boiling flask of a distillation apparatus.

The temperature reading will not change.

Select the reason why boiling stones are added to distillation flasks.

They prevent the formation of very large bubbles by providing surface area for the formation of small bubbles.

Select the description of a column that is used in gas chromatography.

a tube that is 2-4 mm wide and a few meters in length that is packed with inert particles coated with stationary phase

A sample containing acetic acid, benzene, propanoic acid, and octane is injected into a gas chromatograph whose column has a nonpolar stationary phase. Select the compound that will likely have the shortest retention time.

acetic acid

Select the viable application of gas chromatography.

determining the concentrations of organic compounds in a mixture

Which of the following is NOT a technique that can be used to separate two liquids?

filtration

Select the distillation technique that is most effective at separating compounds with boiling points that are within 40 °C of one another.

fractional distillation

Select the factors that affect a compound\'s rate of elution through a gas chromatography column.

the compound\'s boiling point and polarity

Select the correct definition of a compound\'s boiling point.

the temperature at which the compound\'s vapor pressure is equal to the pressure of its surrounding environment

Select the correct definition of retention time in gas chromatography.

the time it takes for a molecule to pass through the column

Which of the following is NOT true about an azeotrope?

An azeotrope boils at a variable temperature.

Which of the following represents the typical volume of sample that is injected into a gas chromatograph?

1-2 μL

While performing a distillation, the relatively steady temperature of the distillation apparatus begins to increase at a moderate rate. What does this most likely indicate? Select the correct answer.

One of the components of the sample has just finished boiling.

Despite having equal molecular weights, the boiling point of n-hexane is higher than that of 2,2-dimethylbutane. Select the reason for this.

2,2-Dimethylbutane is branched. (Despite having an asymmetrical structure, 2,2-dimethylbutane is nonpolar and does not experience dipole-dipole forces. Consider which intermolecular force of attraction is dominant in each molecule, and how the structure of each molecule determines strength of these forces of attraction. )