Newton 4

Question 1

What is the difference in complete and partial separation?

Answer 1

In complete separation you separate all of the compounds in the mixture, in the partial separation you separate just one compound out of the mixture.

Question 2

What is basis of precipitation and filtration?

Answer 2

Difference in solubility of compounds formed.

Question 3

Waht is the basis of distillation?

Answer 3

Difference in volatility of compounds

Question 4

What is the basis of extraction?

Answer 4

Difference in solubility in two immiscible liquids

Question 5

What is the basis of ion exchange?

Answer 5

Difference in interaction of reactants with ion-exchange resin

Question 6

What is the basis of chromstography?

Answer 6

Difference in rate of movement of a solute through a stationary phase

Question 7

What is the basis of electrophoresis?

Answer 7

Difference in migration rate of charged species in an electric field

Question 8

What is the basis of field-flow fractionation?

Answer 8

Difference in interaction with a field or gradient applied perpendicular to transport direction

Question 9

What are the two general common separation categories?

Answer 9

Those that occur between two bulk phases.

Those that occur between a bulk phase and a thin layer

Question 10

What crystallization is used for?

Answer 10

To separate solid state from liquid.

Question 11

What sublimation is used for?

Answer 11

The process of sublimation is used to separate the components of a mixture that possesses one sublimable volatile component and a non- sublimable component often referred to as the impurity.

Question 12

What is sublimation?

Answer 12

When anything solid turns into a gas without first becoming liquid

Question 13

What precipitation - crystallisation involves?

Answer 13

Involves the preferential formation oa a desired solid precipitate of the analyte from a mixture that also contains interfering solutes. These remain in solution and can then be discarded.

Question 14

Before conducting precipitation- crystallisation what are the factors that you need to conseder?

Answer 14

Feasibility of separation can be determined from differences in the solubility or solubility product.

The efficiency of the precipitation step is crytical.

Care to avoid, co-precipitation of soluble material, inclusion and occlusion of impurities.

Question 15

What is liquid-liquid extraction?

Answer 15

It is separation based on their relative solubilities in two different immiscible liquids.

Question 16

How does aqueous ‘wash’ in liquid- liquid extraction works?

Answer 16

You add aqueous solution into the mixture and anything aqueous will move into aqueous layer that you can discard.

Question 17

When doing liquid-liquid extraction what you will think about when choosing solvent?

Answer 17

Consider the solubility of an analyte in each solvent.

Beware of solvents that are mutually soluble with one another, and are prone to form azeotropes.

Consider the difference between the densities of choosen solvents, those with densities that lie close to one another could form emulsions.

Think very carefully about which phase will contain the desired analyte, don’t throw other layers away.

Be careful when using volatile solventsm vapour pressures may develop in the separation.

Question 18

What is azeotrope?

Answer 18

It is a mixture of liquids that has a constant boiling point because the vapour has the same composition as the liquid mixture.

Question 19

What is distribution law?

Answer 19

If the solute species A is allowed to distribute between water and an organic phase, the resulting equilibrium may be written as

A_(aq)<====>A_(org)

Ideally, the ration of activities for A in the two phases will be consistant and independent of the total concentration of A.

K=[A]_org / [A]_aq

Question 20

What is the distribution coefficient (K) used for?

Answer 20

K allows us to establish the concentration of analyte remaining in solution after a certain number of extractions. Also, K provides guidance as tyo the most efficient way to crry out a particular extraction.

Question 21

How can you calculate the remaining concentration of A in liquid-iquid extraction?

Answer 21

Where [A]_i is the concentration of A remaining in the aqueous phase after extracting V_aq mL of the solution, concentration [A]_o, with i portions of organic solvent, each of volume V_org mL

Question 22

What is liquid- liquid continuous extraction?

Answer 22

It is also known as exhaustive extraction, used to isolate solutes with extremely low distribution coefficients. The organic solvents must be less dense than water. Solvent is continually distilled and condenses into long tube immersed in the water. A sufficient ‘head; of solvent in the tube forces it out into the aqueous phase where it can extract the solute. The solvent is continually re-circulated by re-distillation.

Question 23

What is solid-liquid soxhlet extraction?

Answer 23

Sample, often a solid or a resin is placed in a porous thimble in the extractor. The solvent is continually delivered to the extractor thimble by redistillation. The solvent gradually extracts the analyte from the solid matrix. When the thimble is full of solvent it is siphoned back to the solvent reservoir to avoid saturation, maintaining maximum efficiency.