Separations and Purifications . ***

Question 1

extraction

Answer 1

combines two immiscible liquids, one of which easily dissolves the compound of interest.

Question 2

Polar (water) layer is called the

Answer 2

aqueous phase and dissolves compounds with hydrogen bonding or polarity.

Question 3

Organic phase

Answer 3

nonpolar layer and dissolves nonpolar compounds.

Question 4

Extraction is carried out in a

Answer 4

separatory funnel. One phase is collected and the solvent is then evaporated.

Question 5

acid-base properties can be used to

Answer 5

can be used to increase solubility .

Question 6

wash

Answer 6

is the reverse of extraction, in which small amounts of solute that dissolves impurities is run over the compound of interest.

Question 7

Filtration

Answer 7

isolates a solid (residue) from a liquid (filtrate).

Question 8

gravity filtration

Answer 8

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

Question 9

Vacuum filtration

Answer 9

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

Question 10

Recrystallization

Answer 10

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

Question 11

Distillation

Answer 11

separates liquids according to differences in their boiling points; the liquid with the lowest boiling point vaporizes first and is collected as distillate.

Question 12

Simple distillation

Answer 12

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

Question 13

Vacuum distillation

Answer 13

should be used if the boiling points are over 150 C to prevent degradation of the product.

Question 14

Fractional distillation

Answer 14

should be used if the boiling points are less than 25 C apart because it allows more refined separation of liquids by boiling points.

Question 15

Chromatography

Answer 15

use two phases to separate compounds base on physical or chemical properties.

Question 16

Stationary phase or adsorbent

Answer 16

is usually a polar solid .

Question 17

Mobile phase

Answer 17

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

Question 18

Compounds with higher affinity for the stationary phase have smaller

Answer 18

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

Question 19

Thin layer and paper chromatography

Answer 19

are used to identify a sample:
-stationary phase is polar material, such as silica, alumina, or paper.
-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.
reverse-phase chromatography uses a nonpolar card with a polar solvent.

Question 20

column chromatography

Answer 20

utilizes polarity, size or affinity to separate compounds based on their physical or chemical properties.

• stationary phase is column containing silica or alumina beads.
• mobile phase is a a nonpolar solvent, which travels through the column by gravity.

Question 21

Ion-exchange chromatography

Answer 21

beads are coated with charged substances to bind to compounds with opposite charge.

Question 22

size-exclusion chromatography .

Answer 22

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

Question 23

affinity chromatography

Answer 23

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

Question 24

Gas chromatography

Answer 24

separates vaporizable compounds according to how well they adhere to the adsorbent in the column.

• stationary phase is a coil of crushed metal or a polymer
• the mobile phase is a nonreactive gas
• gas chromatography may be convinced in sequence with mass spectrometry, which 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

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

Question 26

retardation factor

Answer 26

Rf = distance spot moved/distance solvent front moved

Question 27

Extraction depends on what three intermolecular force

Answer 27

1. hydrogen bonding: like alcohols, acids, will move to aq layer
2. dipole-dipole interactions: these are less likely to move to aq
3. vander waals: with only these, compounds are least likely move to the aq