CH 236 UAB Lab final

What are the 7 steps to recrystallization

Selecting a solvent

Dissolution

Decolorization

Filtration (impurities)

Crystallization

Filtration (compound)

Drying

What are the properties of a good solvent for recrystallization

The solid must be poorly soluble at room temperature and highly soluble at the boiling point

Why are boiling chips added

It prevents superheating and helps the solution to boil all together

Prevents bumping

When must decolorization take place during recrystallization

Only when colored impurities exist

What is a saturated solution

When a solvent holds the maximum amount of solute at a given temperature

What is the procedure for facilitating the crystallization of a solid

Allow the solution to cool slowly

After the solution has cooled, place the flask into an ice bath

Scratch the inside of the flask with a glass stirring rod

What does crystallization form

A crystalline solid

What does precipitation form

An amorphous solid

What are the characteristics of the melting point of a pure compound

An accurate melting point with a narrow range

What are the characteristics of the melting point of an impure compound

A low and broad melting point range

How is a mixed melting point used to determine the identity of a compound

First, the melting point range of the unknown compound is found

Next, the suspected known compound for the identity of the unknown is identified

Lastly, a mixed melting point is found by making a 50/50 mixture of the suspected known and unknown compounds. If the melting point of the mixture matches that of the unknown and the known while also having a narrow range, the unknown compound has been identified as the known compound.

What is bumping

Instantaneous eruption of vapor from a hot liquid

What are the components of a simple distillation apparatus

Long necked round bottom flask, Distillation head, rubber connector with support rod, Thermometer adapter, and thermometer

What are the components of the fractional distillation apparatus

Short-necked round bottom flask, distillation head, long distillation column, rubber connector with support rod, thermometer adapter, and thermometer, copper turnings

Draw a simple and fractional distillation apparatus and show the difference between the two

Simple distill

When should you use fractional distillation over simple distillation

Fractional distillation should be used when the two unknowns have boiling points that are less than 75 celsius different. This is due to the theoretical plates.

What is a theoretical plate

In fractional distillation, the turnings allow for the consecutive condensation and revaporization along multiple levels throughout the distillation column. The substance that condenses and revaporizes is the substance with the lower boiling point. This allows the distillate to be 100% pure of the lower boiling point.

Where is the thermometer placed during distillation

It is placed with the top of the mercury bulb level with the bottom of the arm of the distillation head.

Why is it important not to distill to dryness

The dry residue can contain peroxides which can ignite or explode without other liquid in the flask

Why do you use a rheostat with the sand bath

It allows you to vary the amount of power to the sand bath. This allows the substance to be distilled low and slow

Draw the mechanism for the hydrolysis of t-butyl chloride

T-butyl chloride

Draw the mechanism for the dehydration of 2-methyl-cyclohexanol

Dehydration

What is retention time in gas chromatography

The time it takes for a compound to travel through the column

In regards to boiling point, which substances travel through the column of gas chromatography the quickest

Those with lower boiling points or higher volatility

What 4 factors affect separation in gas chromatography

Volatility of the compound, Flow rate of carrier gas, column temperature, and column length

What does the area under a peak of gas chromatography represent

The amount of that substance in the mixture

Hod do you calculate the percent of a substance A in a mixture based off of gas chromatography

Area under peak A divided by

Area under peaks A + B + C

Times 100