Crystallization

Question 1

is the formation of solid particles within a homogeneous phase.

Answer 1

Crystallization

Question 2

Crystallization may be carried out from

Answer 2

vapor, melt, or solution

Question 3

Most of the industrial applications of crystallization involve crystallization from

Answer 3

Solutions

Question 4

formation of solid particles in a vapor

Answer 4

Snow

Question 5

solidification from a liquid melt

Answer 5

as freezing of water to ice

Question 6

formation of solid crystals from a solution

Answer 6

as the formation of Glauber’s salt from Na2SO4 solution

Question 7

is the process whereby a solution is supersaturated so as to cause formation of crystals

Answer 7

Crystallization

Question 8

Its wide use has two - fold basis:

Answer 8

1. A crystal formed from an impure solution is itself pure (unless mixed crystals occur)
2. Crystallization affords a practical way of obtaining pure chemical substance in a satisfactory condition for packaging and storing.

Question 9

The rate of crystallization involves two distinct actions:

Answer 9

1. The rate of formation of new crystals (nucleation)
2. The rate of precipitation on crystals already present (crystal growth to macroscopic size)

Question 10

The two rates of crystallization’s driving force

Answer 10

supersaturation

Question 11

The two rates of crystallization can’t occur in

Answer 11

a saturated or undersaturated solution

Question 12

Methods of supersaturating the solutions:

Answer 12

1. By cooling
2. By evaporation of solvent
3. By adiabatic evaporation with cooling
4. By addition of a third component where the solubility of the solute is sharply reduced
5. By addition of a third component which will react with original solute to form an insoluble product.

Question 13

The extent of the supersaturation depends upon

Answer 13

1. The number and shape of crystals upon which precipitation occurs
2. The temperature levels
3. The solution concentration
4. The violence of the agitation present

Question 14

The heat effects in a crystallization process can be computed by two methods:

Answer 14

1. A heat balance
2. An enthalpy balance

Question 15

can be made in which individual heat effects such as sensible heats, latent heats, and the heat of crystallization can be combined into an equation for total heat effects.

Answer 15

heat balance

Question 16

can be made in which the total enthalpy of all leaving streams minus the total enthalpy of all entering streams is equal to the heat absorbed from external sources by the process.

Answer 16

enthalpy balance

Question 17

The advantage of the enthalpy - concentration diagram method is

Answer 17

both heat and mass effects are taken into account simultaneously.

Question 18

In using heat balance method, it is necessary to make ________, since the heat effects are related to the quantities of solids produced through the heat of crystallization

Answer 18

a corresponding mass balance

Question 19

This method has only limited use, however, because of the difficulty in obtaining enthalpy - concentration data.

Answer 19

heat balance

Question 20

With compounds whose solubility increases with increasing temperature there is an absorption of heat when the compound dissolves which is called the

Answer 20

heat of solution

Question 21

When there is no change in solubility with temperature,

Answer 21

there is no heat effect.

Question 22

are generally reported as the change in enthalpy associated with the dissolution of a large quantity of solute in excess of pure solvent.

Answer 22

Heat of solution

Question 23

is equal and opposite in sign to the heat of solution.

Answer 23

heat of crystallization

Question 24

Using the heat of solution at infinite dilution as equal but opposite in sign to the heat of crystallization is equivalent to neglecting

Answer 24

heat of dilution

Question 25

A solution that contains as much of a dissolved solute as it can hold is said to be ________ with that solute.

Answer 25

saturated

Question 26

If a saturated solution is cooled, the solubility of the solute ___

Answer 26

Decreases

Question 27

Equilibrium relations for crystallization are expressed in the form

Answer 27

solubility data

Question 28

Solubility data are ordinarily given as

Answer 28

parts by weight of anhydrous crystals per 100 parts by weight of total solvent

Question 29

Solubility data can be presented efficiently and clearly in ________, which show equilibrium compositions in a system as functions of one or more system variables.

Answer 29

phase diagrams

Question 30

The usual phase diagram for a solid-liquid system is

Answer 30

a plot of temperature versus mass fraction of the solid.