Organic Chemistry Separation

Question 1

One way of separating out a desired product is through extraction, the transfer of a dissolved compound from one solvent into another in which the product is more soluble. Most impurities left behind in the first solvent. The two solvents should be immiscible (form two layers that do not permanently mix because of mutual insolubility). The two layers are temporarily mixed together, by shaking the container and venting any gas formed, so the solute can pass from one layer to the other. ___ separates substances based on differential solubility in aqueous versus organic solvents

Answer 1

extraction

Question 2

The ___ and ether (organic) phases are separated in a specialized piece of glassware called a separatory funnel. Once separated, the isobutyric acid can be isolated from the aqueous phase in pure form Some isobutyric acid will remain dissolved in the ether phase, so the extraction should be repeated several times with fresh solvent (water). More product can be obtained with successive extractions (e.g., it is more effective to perform three successive extractions of 10 mL each than t perform one extraction of 30 mL). Once the compound has been isolated in its purified form in a solvent, it can then be obtained by evaporation of the solvent

Answer 2

water (aqueous)

Question 3

___ depends on the basic rule of solubility: “like dissolves like.”

1. Hydrogen bonding: compounds that can do this, such as alcohols or acids, will move most easily into the aqueous layer, which also can form hydrogen bonds
2. Dipole-dipole interactions: compounds with these interactions are less likely to move into the aqueous layer because doing so requires breaking the hydrogen bonds of the solvent and replacing them with weaker dipole-dipole bonds
3. London dispersion forces: compounds with only these interactions are least likely to move into the aqueous layer because breaking the hydrogen bonds of the solvent without replacing them with any significant bonds takes large amounts of energy

Answer 3

extraction

Question 4

The ___ of acids and bases also can be used to advantage in extraction:
HA + base -> A- + Base: H+
When the acid dissociates, the anion formed will be more soluble in the aqueous layer than the original form. This is because the charged anions will form ion-dipole bonds with the solvent, which are even stronger than the hydrogen bonds they are displacing. thus, adding a base will help extract an acid into an aqueous layer
An extraction carried out to remove unwanted impurities rather than to isolate a pure product is called a wash

Answer 4

properties

Question 5

___ is used to isolate a suspended solid from a liquid. In this technique, a liquid/solid mixture is poured onto a paper filter that allows only the solvent to pass through. The result of this process is the separation of the solid (the residue) from the liquid (the filtrate)

Answer 5

filtration

Question 6

The two basic types of filtration are gravity filtration and vacuum filtration.
In ___, the solvent’s own weight pulls it through the filter. Frequently, however, the pores of the filter become clogged with solid, slowing the rate of filtration. For this reason, in gravity filtration it is generally desirable for the substance of interest to be in solution (dissolved in the solvent), while impurities remain undissolved and can be filtered out. This allows the desired product to flow more easily and rapidly through the apparatus. To ensure the product remains dissolved, gravity filtration is usually carried out with hot solvent, since increasing heat generally increases K sub sp. the solvent is later evaporated.
In vacuum filtration, the solvent is forced through the filter by a vacuum on the other side. Vacuum filtration is used to isolate relatively large quantities of solid, usually when the solid is the desired product

Answer 6

gravity filtration

Question 7

___ is a process in which impure crystals are dissolved in a minimum amount of hot solvent. As the solvent is cooled, the crystals re-form, leaving the impurities in solution. For recrystallization to be effective, the solvent must be chosen carefully. It must dissolve the solid while hot but not while cold. In addition, it must dissolve the impurities at both temperatures so they remain in solution even after being cooled. In this way, recrystallization separates solids based on differential solubility at a given temperature

Answer 7

recrystallization

Question 8

___ choice is usually a matter of trial and error, although some generalization scan be made. Ideally the desired product should have solubility that depends on temperature - it should be more soluble at high temperature and less so at low. In contrast, impurities should be equally soluble at various temperatures. An estimate of polarity is useful since polar solvents dissolve polar compounds, whereas non polar solvents dissolve nonpolar compounds. A solvent with intermediate polarity is generally desirable in recrystallization. In addition, the solvent should have a low enough freezing point that the solution may be sufficiently cooled without turning to a solid.
In some instances, a mixed solvent system may be used. Here, the crude compound is dissolved in a solvent in which it is highly soluble. Another solvent in which the compound is less soluble is then added in drops until the solid just begins to precipitate. the solution is heated a bit more to redissolve the precipitate and then slowly cooled to induce crystal formation

Answer 8

solvent

Question 9

Sublimation occurs when a heated solid turns directly into a gas without an intervening liquid stage. it is used as a method of purification because the impurities found in most reaction mixtures will not sublimate easily and separates solids based on their ability to sublimate. The vapors are made to condense on a cold finger, a piece of glassware packed with dry ice or with cold water running through it. Most sublimations are performed under vacuum because to higher pressures more compounds will pass through a liquid phase rather than subliming. Low pressure also reduces the temperature required for sublimation and thus the danger that the compound will decompose. The ___ depend on the compound to be purified since each compound has a different phase diagram

Answer 9

optimal conditions

Question 10

___ in an solution settle, or sediment, at different rates depending upon their mass, density, and shape. Sedimentation can be accelerated by centrifuging the solution. A centrifuge is an apparatus in which test tubes containing the solution are spun at high speed. This subjects them to centrifugal force. Compounds of greater mass and density settle toward the bottom of the test tube, while lighter compounds remain near the top. This method of separation is effective for many different types of compounds and is frequently used in biochemistry to separate cells, organelles, and biological macromolecules

Answer 10

particles

Question 11

___ depends on Size (mass) and Density

Answer 11

sedimentation

Question 12

Distillation is the separation of one liquid from another through vaporization an d condensation. A mixture of two or more miscible liquids is slowly heated. the compound with the lowest boiling point is preferentially vaporized, condensed on a water-cooled distillation column, and separated from the other, higher-boiling point compound(s). Note that immiscible liquids can be separated in a separatory funnel and thus do not require distillation.
___ is strongly affected by intermolecular forces, with stronger intermolecular forces requiring more energy (higher temperature) to break. This is why H2O ( with hydrogen bonds( has such a high boiling point and why longer molecules (with more London dispersion forces) tend to have higher boiling points than shorter ones

Answer 12

boiling point

Question 13

___ is used to separate liquids that have boiling points that are below 150 degrees Celsius and that are at least 25 degrees Celsius apart from one another. The apparatus consists of a distilling flask containing the two liquids, a distillation column consisting of a thermometer and a condenser, and a receiving flask to collect the distillate

Answer 13

simple distillation

Question 14

___ is used to separate liquids that have boiling points above 150 degrees Celsius and that are at least 25 degrees Celsius apart. The entire system is operated under reduced pressure, lowering the boiling points of the liquids and preventing their decomposition due to excessive temperature

Answer 14

vacuum distillation

Question 15

___ is used to separate liquids that have boiling points that are less than 25 degrees Celsius apart. A fractionating column is used to connect the distilling flask to the distillation column. It is filled with inert objects, such as glass beads, that have a large surface area. The vapors condense on these surfaces, re-evaporate, and then condense further up the column. Each time the liquid evaporates, the vapors contain a greater proportion of the lower-boiling-point component. Eventually, the vapor near the top of the fractionating column is composed solely of one component, which condenses on the distillation column and collects in the receiving flask

Answer 15

fractional distillation

Question 16

___ is a technique that allows the separation and identification of individual compounds from a complex mixture based on their differing chemical properties. Chromatography separates compounds based on how strongly they adhere to a stationary phase versus a mobile phase.
First, the sample is loaded into the stationary phase, which is a solid medium also called adsorbent. Then the mobile phase, which is a fluid, is run through the stationary phase to displace (or elute) adhered substances. Different compounds will adhere to the stationary phase with different strengths and therefore migrate with different speeds. This causes separation of the compounds within the stationary phase, allowing each compound to be isolated

Answer 16

chromatography

Question 17

How quickly a compound travel through the stationary phase depends on a variety of factors. Several forms of media are used as the stationary phase in order to separate compounds based on different chemical properties. Chromatography is often done with silica gel as the adsorbent because it is very polar and hydrophilic. The ___, usually an organic solvent of weak to moderate polarity, is then used to run the sample through the gel. In this situation, non polar compounds move very quickly because they dissolve well in the nonpolar mobile phase, whereas polar molecules stick tightly to the polar stationary phase

Answer 17

mobile phase

Question 18

___ is just the opposite. In this process, the stationary phase is very nonpolar, so polar molecules run very quickly, while nonpolar molecules stick more tightly

Answer 18

reverse-phase chromatography

Question 19

Size or charge may also play a ___, as in column chromatography. Newer techniques, such as affinity chromatography, take advantage of unique properties of a substance, such as its ability to bind to a specific antibody, receptor, or ligand, in order to bind it to the stationary phase

Answer 19

role

Question 20

___ can be distinguished from each other because they travel across the stationary phase (adsorbent) at different rates. In practice, a substance can be identified based on how far it travels in a given amount of time (as in thin-layer chromatography) or how rapidly it travels a given distance (e.g., how quickly it elutes off the column in gas or column chromatography)

Answer 20

compounds

Question 21

The ___, or plate, in thin-layer chromatography (TLC) is either a piece of paper or a thin layer o silica gel or alumina on a plastic or glass sheet. The mixture to be separated is placed on the adsorbent; this is called spotting because a small, well-defined spot is desirable. The TLC plate is then developed-placed upright in a developing chamber (usually a wide-mouthed jar or a beaker with a lid) containing eluent (solvent) approximately one-fourth of an inch deep (this value depends on the size of the plate). It is imperative that the initial spots on the plate be above the level of the solvent, or else they will simply elute off the plate into the solvent rather than moving up the plate itself. The solvent creeps up the plate by capillary action, with different compounds moving at different rates depending on their affinity for the plate versus the solvent. When the solvent front nears the top of the plate, the plate is removed from the chamber and allowed to dry.

Answer 21

adsorbent

Question 22

The spots of individual compounds are not usually visible on the white TLC plate. they are instead visualized by placing the ___ under UV light, which shows any compounds that are UV-sensitive, or by allowing iodine to stain the spots. Other chemical staining agents include phosphomolybdic acid and vanillin. Note that these compounds destroy the product, and it cannot be recovered for further study

Answer 22

TLC plate

Question 23

The ___ a compound travels divided by the distance the solvent travels is called the Rf value. This value is relatively constant for each unique compound in a particular solvent and can therefore be used for identification.
TLC is most frequently used for qualitative identification (i.e., determining the identity of a compound) rather than separation. Nevertheless, it can also be used on a larger scale as a means of purification. Preparative or prep TLC uses a large TLC plate upon which a sizeable streak of mixture is placed. As the plate develops, the streak splits into bands of individual compounds, which can then be scraped off. Rinsing with a polar solvent will recover the pure compounds from the silica

Answer 23

distance

Question 24

The principle behind ___ is the same as for TLC. Column chromatography, however, uses silica gel or alumina as an adsorbent (not paper), and this adsorbent is in the form of a poured or packed column, which allows much more separation. In TLC, the solvent and compounds move up the plate due to capillary action, whereas in column chromatography they move down the column due to the force of gravity. Sometimes the solvent is forced through the column with nitrogen gas; this is called flash column chromatography

Answer 24

column chromatography

Question 25

The ___ drips out of the end of the column, and fractions are collected in flasks or test tubes. These fractions contain bands corresponding to the different compounds. When the solvents are evaporated, the compounds can be isolated. In column chromatography, the silica/alumina packing is highly polar. Hence, the nonpolar fraction will be collected in the collection flasks

Answer 25

solvent

Question 26

___ is particularly useful in biochemistry because it can be used to separate macromolecules, such as proteins or nucleic acids
In ion exchange chromatography, the beads in the column are coated with charged substances so they will attract or bind compounds with an opposing charge. or instance, a positively charged column will attract and hold negative substances while letting those with positive charge pass through.
In size-exclusion chromatography, the column contain beads with many tiny pores. Very small molecules can enter the beads, which slows down their progress, while large molecules move around the beads and thus travel through the column faster
In affinity chromatography, columns can be customized to bind a substance of interest. To purify substance A, a scientist might use a column of beads coated with something that binds A very tightly, such as a receptor for A, A’s biological target, or even a specific antibody. This will cause substance A to bind to the column very tightly. Substance A can later be eluted by watching with free receptor (or target or antibody), which will compete with the bead-bound receptor and ultimately free substance A from the column

Answer 26

column chromatography

Question 27

___ (GC) is another method of qualitative separation. In gas chromatography, also called vapor-phase chromatography (VPC), the eluent that passes through the adsorbent is a gas, usually helium or nitrogen. The adsorbent is inside a 30-goot column that is coiled and kept inside an oven to control its temperature. The mixture to be separated is injected into the column and vaporized. the gaseous compounds travel through the column at different rates because they adhere to the adsorbent to different degrees and will separate by the time they reach the end of the column. At this point, they are registered by a detector, which records the presence of a compound as peak. To identify a compound or distinguish between two different compounds, the retention times (how long it took for each to travel through the column) are compared

Answer 27

gas chromatography

Question 28

GC can be used on a larger scale for ___; it is then called preparative, or prep, GC. However, this is very tedious and difficult to perform and is rarely done.

Answer 28

quantitative separation

Question 29

HPLC stands for either high-pressure or high-performance ___. The eluent is a liquid that travels through a column similar to a GC column, but it is under pressure. In the past, very high pressures were used. Now much lower pressures can be used, hence the change from high pressure to high performance.
In HPLC, a sample is injected into the column, an d separation occurs as it is pumped through. The compounds pass through a detector an dare collected as the solvent flows out of the end of the apparatus. The eluent may vary, as in thin-layer or column chromatography. The additional pressure allows for the separation of even very small samples and an increased resolving power, making HPLC a good choice when fine detail is needed, as in medical applications

Answer 29

liquid chromatography

Question 30

When a molecule is placed in an electric field, it will move toward either the cathode or the anode, depending on its size and change. ___ employs this phenomenon to separate macromolecules, such as proteins or DNA. The migration velocity, v, of a molecule is directly proportional to the electric field strength, E, and to the net charge on the molecule, z, and is inversely proportional to a frictional coefficient, f, which depends on the mass and shape of the migrating molecules. Therefore, in a constant electric field, highly charged, small molecules will move most rapidly. Note that, in most forms of electrophoresis, the size of a macromolecule is the most important factor-small molecules move faster, whereas large ones move more slowly and may in fact take hours to leave the well

Answer 30

electrophoresis

Question 31

___ is used by molecular biologists to separate pieces of nucleic acid (usually deoxyribonucleic acid, but sometimes ribonucleic acid as well). Agarose is an organic gel derived from seaweed that is nontoxic and easy to manipulate. Since every piece of nucleic acid is highly negatively charged, nucleic acids can be separated effectively on the basis of size without any additional treatment to create or manage charge. Agarose gels are stained with a compound called ethidium bromide, which binds to nucleic acids and is visualized by its fluorescence under ultraviolet light. Agarose gel electrophoresis can also be used preparatively by cutting the desired band out of the gel an diluting out the nucleic acid

Answer 31

agarose gel electrophoresis

Question 32

SDS-polyacrylamide gel electrophoresis separates ___ on the basis of mass, not charge. Polyacrylamide gel (PAGE) is the standard medium for electrophoresis. SDS is sodium dodecyl sulfate, which disrupts noncovalent interactions. SDS binds to proteins and creates large negative net charges, overriding the protein’s original net charge. Therefore, as proteins move through the gel, the only variable affecting their velocity is f, the frictional coefficient, which is dependent on mass. After separation, the gel is stained so the protein bands can be visualized

Answer 32

proteins

Question 33

A protein may be characterized by its ___, pI, which is the pH at which the sum of the charges on all of its component amino acids (its net charge) is zero. Since amino acids and protein are organic molecules, the fundamental principles of acid-base chemistry apply to them as well

Answer 33

isoelectric point

Question 34

At a low pH, [H+] is relatively high. Thus, at a pH < pI, proteins will tend to be ___ and, as a result, positively charged. At a relatively high (basic) pH, [H+} is fairly low and proteins will tend to be deprotonated, thus carrying a negative charge

Answer 34

protonated

Question 35

If a mixture of proteins is placed in an electric field in a gel with ah pH gradient, the proteins will move until they reach the point at which the pH is equal to their pI. At this location, the protein will be uncharged and will no longer move in the field. ___ differing by as little as one charge can be separated in this manner, which is called isoelectric focusing.

Answer 35

molecules

Question 36

___ is a technique used to separate biological macromolecules. The sample (proteins, DNA, or RNA) are transferred onto a substrate, usually nitrocellulose. This technique often follows the electrophoresis steps above. After the blotting, a visualization stain is used to help isolate the sample. Southern blots are used to visualize DNA, northern blots are used for RNA and western blots are used for proteins

Answer 36

blotting

Question 37

___, Northern, o, Western DNA, RNA, o, protein

Answer 37

Southern, SNoW DRoP