Ch. 12: Separations and Purifications

Question 1

Extraction

Answer 1

Combines 2 immiscible liquids, one of which easily dissolves the compound of interest. Carried our in a separatory funnel. One phase is collected and the solvent is then evaporated. Acid base properties can be used to increase solubility.

Question 2

Extraction: aqueous phase

Answer 2

The polar (water) layer is called the aqueous phase and dissolves compound w hydrogen bonding or polarity.

Question 3

Extraction: organic phase

Answer 3

The nonpolar layer is called the organic phase and dissolves nonpolar compounds.

Question 4

Wash

Answer 4

Reverse of extraction: a small amount of solute that dissolves impurities is run over the compound of interest

Question 5

Filtration

Answer 5

Isolates a solid (residue) from a liquid (filtrate)

Question 6

Gravity filtration

Answer 6

Used when the product of interest is in the filtrate. Hot solvent is used to maintain solubility.

Question 7

Vacuum filtration

Answer 7

Used when the product of interest is the solid. A vacuum is connected to the flask to pull the solvent through more quickly

Question 8

Recrystallization

Answer 8

The product is dissolved in a minimum amt of hot solvent. If the impurities are more soluble the crystals will reform while the flask cools, excluding the impurities

Question 9

Distillation

Answer 9

Separates liquids according to differences in their boiling points. The liquid w the lowest boiling point vaporizes first and is collected as the distillate.

Question 10

Simple distillation

Answer 10

Can be used if the boiling points are under 150C and are at least 25 apart

Question 11

Vacuum distillation

Answer 11

Should be used if the boiling point s are over 150*C to prevent degradation of the product

Question 12

Fractional Distillation

Answer 12

Should be used if the boiling points are less than 25*C apart bc it allows for more refined separation of liquids by boiling point

Question 13

Chromatography

Answer 13

Use two phases to separate compounds based on physical or chemical properties

Question 14

Stationary phase or adsorbent

Answer 14

In chromatography, Usually a polar solid

Question 15

Mobile phase

Answer 15

In chromatography, the mobile phase runs through the stationary phase and is usually a liquid or gas. This elutes the sample through the stationary phase

Question 16

Retardation factors (chromatography)

Answer 16

Compounds w higher affinity for the stationary phase have smaller retardation factors and take longer to pass through, if at all; compounds w higher affinity for the mobile phase elute through more quickly. Compound therefore get separated from each other, called partitioning

Question 17

Thin layer and paper chromatography

Answer 17

Used to identify a sample. The stationary phase is a polar material, such as silica, alumina, or paper. The mobile phase is a nonpolar solvent which climbs the card through capillary action. The card is spotted and developed; Rf values can be calculated and compared to reference values

Question 18

Reverse phase chromatography

Answer 18

Uses a nonpolar card w a polar solvent

Question 19

Column Chromatography

Answer 19

Utilizes polarity, size, or affinity to separate compounds based on their physical or chemical properties. The stationary phase is a column containing silica or alumina beads. The mobile phase s a nonpolar solvent, which travels through the column by gravity

Question 20

Ion-exchange chromatography

Answer 20

The beads are coated w charged substances to bind compounds w opposite charge

Question 21

Size exclusion chromatography

Answer 21

The beads have small pores which trap smaller compounds and allow larger compounds to travel through faster

Question 22

Affinity chromatography

Answer 22

The column is made to have high affinity for a compound by coating the beads w a receptor or antibody to the compound

Question 23

Gas chromatography

Answer 23

Separates vaporizable compounds according to how well they adhere to the adsorbent in the column. The stationary phase is a coil of crushed metal or a polymer. The mobile phase is a nonreactive gas. May be combined w mass spectrometry

Question 24

Mass spectrometry

Answer 24

Ionizes and fragments molecules and passes these fragments through a magnetic field to determine molecular weight or structure

Question 25

High performance liquid chromatography (HPLC)

Answer 25

Similar to column chromatography but uses sophisticated computer mediated solvent and temp gradients. It is used if the sample size is small or if forces such as capillary action will affect results. It was formerly called high pressure liquid chromatography