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Ph@rm@ > Module 4 > Flashcards

Module 4 Flashcards

1
Q

______ is a separation and purification technique employed to produce a wide variety of materials.

A

Crystallization

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2
Q

Examples of crystalline
materials:

A

a. Quartz
b. Salt (Himalayan salt)
c. Acetylsalicylic acid
(Aspirin)
d. Sugar

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3
Q

__________ may be defined as a phase change in which
a crystalline product is obtained from a __________

A

Crystallization; homogeneous
phase.

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4
Q

A crystal may come from any of the following homogeneous phases:
1. A liquid ______ consisting of a solvent (liquid) and a solute (solid) at the condition of interest.

A

solution

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5
Q

A crystal may come from any of the following homogeneous phases:
2. A _________ , which is a material that is solid at normal conditions but becomes a molten liquid when heated.

A

melt

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6
Q

Crystallization may be defined as a phase change in which
a crystalline product is obtained from homogeneous
phase. 3. A gaseous mixture; i.e., a solution of a solid in a ________

A

supercritical fluid

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7
Q

Crystallization can be regarded as a self-assembly process in
which randomly organized molecules in a fluid come together
to form an _________

A

ordered three-dimensional molecular array with a
periodic repeating pattern.

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8
Q

Crystallization is vital to many processes: both ________ and
.

A

natural; man-made

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9
Q

Crystals are solids in which
the atoms, ions, or molecules
are arranged in a ______
repeating pattern that
extends in ________.

A

periodic; three dimensions

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10
Q

All crystals are ________ but not all
solids are crystals. Materials that have short-range ordering are described as _______ solids.

A

solids; amorphous

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11
Q

A crystal can be represented as a geometric point lattice –
a set of points arranged so that each point has identical
surroundings.

A

Unit cell

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12
Q

The lengths and angles in
a lattice point system are
known as ________.

A

lattice
parameters

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13
Q

A single cell constructed
using the parameters is
called a ___________.

A

unit cell

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14
Q

The representation of planes
in a lattice makes use of
______________.

A

Miller indices {hkl}

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15
Q

If a plane is parallel to a
given axis, the Miller index
is __________.

A

zero

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16
Q

Negative indices are
written with ________ over
them

A

bars

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17
Q

Step 1:
Identify the __________ on the x-,y-,z- axes

A

intercepts

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18
Q

Step 2: Specify the intercepts in ________ co-ordinates

A

fractional

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19
Q

Step 3:
Take the _________ of the fractional intercepts

A

reciprocals

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20
Q

While it seems possible that a number of different lattice
arrangements and unit cells can be constructed, Bravais in
1848, showed that only ____ possible point lattices can be
constructed.

A

14

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21
Q

These 14 point lattices can be divided into _____ crystal
systems.

A

7

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22
Q

Simple/Primitive (P) Crystal systems

A

Triclinic
Monoclinic
Orthorhombic
Tetragonal
Cubic
Trigonal/rhombohedral
Hexagonal

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23
Q

Body Centered (I) systems

A

Orthorhombic
Tetragonal
Cubic

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24
Q

Face Centered (F) systems

A

Orthorhombic
Cubic

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25
Q

Base Centered (C) systems

A

Monoclinic
Orthorhombic

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26
Q

Cubic (axial relationships)

A

a = b = c

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27
Q

Cubic (interaxial angles)

A

alpha = beta = gamma = 90

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28
Q

Hexagonal (axial relationships)

A

a = b =/= c

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29
Q

Hexagonal (interaxial angles)

A

alpha = beta = 90, gamma = 120

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30
Q

Tetragonal (axial relationships)

A

a = b =/= c

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31
Q

Tetragonal (interaxial angles)

A

alpha = beta = gamma = 90

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32
Q

Rhombohedral (axial relationships)

A

a = b = c

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33
Q

Rhombohedral (interaxial angles)

A

alpha = beta = gamma =/= 90

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34
Q

Orthorhombic (axial relationships)

A

a =/= b =/= c

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35
Q

Orthorhombic (interaxial angles)

A

alpha = beta = gamma = 90

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36
Q

Monoclinic (axial relationships)

A

a =/= b =/= c

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37
Q

Monoclinic (interaxial angles)

A

alpha = gamma = 90 =/= beta

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38
Q

Triclinic (axial relationships)

A

a =/= b =/= c

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39
Q

Triclinic (interaxial angles)

A

alpha =/= beta =/= gamma = 90

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40
Q

Amorphous state: atoms or molecules possess no ______, and are organized in essentially a random arrangement.

A

long-range periodicity

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41
Q

Amorphous state is considered as the ______ of a crystalline material.

A

antithesis

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42
Q

For amorphous materials,
the diffraction pattern
would exhibit a broad _____
with ______
maximum.

A

halo; few or a single

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43
Q

Crystalline materials
would have characteristic
__________ peaks that
correspond to the
different ________ planes
within the crystal lattice.

A

diffraction; symmetry

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44
Q

________ are restricted in a crystalline solid – ______ systems
and less susceptible to chemical degradation.

A

Molecules; static

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45
Q

The area of research involved in understanding the true
nature of crystals and how they are identified based on
knowledge of crystal’s internal structure.

A

Crystallography

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46
Q

Law that shows the crystal identification using the XRD where the angle of the incident x-ray is equal to the diffracted x-ray angle.

A

Bragg’s Law

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47
Q

Constructive interference occurs when n*pi = ______ for Bragg’s Law.

A

2dsin(theta)

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48
Q

Different crystal
forms of the same
compound will exhibit
_______ XRD spectra

A

different

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49
Q

The development, design, and control of a crystallization
process involve knowledge of a number of the properties
of the solution.
* As an example, ________ provides the concentration at which the
solid solute and the liquid solution are at equilibrium.

A

solubility

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50
Q

The solubility data allows calculation of the _______ accompanying a change of state from one concentration to another in which crystals form.

A

maximum yield of product crystals

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51
Q

Mass balance plays an important part on crystallization
process design, development, and experimentation;
however, it tells us nothing about the ______ at which the
crystals form and the _____ required to obtain this amount
of solid.

A

rate; time

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52
Q

Crystallization is a rate process, depending on a driving
force called __________ .

A

supersaturation

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53
Q

The amount of solute required to make a saturated solution at a given condition is called ___________.

A

solubility

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54
Q

The solubility of materials depends on_______. The information provided by solubility is vital in crystallization processes.

A

temperature

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55
Q

_________ solubility is seen to have a relatively weak
temperature dependence. _______, by contrast, have really high temperature dependence.

A

Sodium chloride; Potassium nitrate

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56
Q

The solubility of common salts is important because it will determine the amount of ______ required to yield a given amount of product
and whether ________ will provide a reasonable product yield

A

cooling

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57
Q

Curve 1 (e.g. KNO3): ↑T, ↑solubility: ________ a solution is preferred for
those with steep slopes

A

Cooling

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58
Q

Curve 2 (e.g. NaCl) Solubility is almost independent of T; _________ of solution is preferred

A

Evaporation

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59
Q

Curve 3 (e.g. MnSO4∙H2O) : ↓T, ↑sol.
* _________ solubility curve

A

Inverted

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60
Q

The solubility of a compound in a particular solvent is part
of the system phase behavior and can be described graphically by a ________.

A

phase diagram

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61
Q

In phase diagrams of solid-liquid equilibria, the _________ of the solid is usually plotted versus .

A

mass fraction; temperature

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62
Q

The line abcdef is the saturation line that defines a _______ at a given temperature

A

saturated solution

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63
Q

Line ab is the solubility line for the
_____ (when a solution in this region is cooled, _____ crystallizes out and is in equilibrium with the solution)

A

solvent; ice

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64
Q

Point b is the _________ (at this point both ______ will separate as solids)

A

eutectic point; ice and MgSO4

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65
Q

The curve bcdf represents the solubility curve of ________

A

MgSO4

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66
Q

A solution in which the
solute concentration
exceeds the equilibrium
(saturation) solute
concentration at a given
temperature is known
as a ________.

A

supersaturated
solution

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67
Q

It is important to note that a supersaturated solution is considered __________.

A

metastable

68
Q

__________ involves cooling to change solubility.

A

Temperature change

69
Q

_____________ is useful when solvent is non-aqueous with removal of solvent increasing solute concentration.

A

Evaporation of solvent

70
Q

Changing solvent composition happens with addition of an _______ (a specific solvent which causes
solubility to decrease greatly)
- the __________ where the solute is not soluble but miscible to the
system

A

antisolvent

71
Q

_______ causes supersaturation by precipitation.

A

Chemical reaction

72
Q

Referring to the solubility diagram:
If we start with a solution at point 1
and cool it to point 2 just below
saturation, the solution would be
supersaturated. However, crystals
________ to form.

A

may take days

73
Q

Referring to the solubility diagram: If we have a sample cooled further
to point 3, crystallization might
occur in _______.

A

a matter of hours

74
Q

Cooling a sample beyond point 3, the solution becomes ________ and
crystallization occurs _______.

A

unstable; spontaneously

75
Q

The area between the point
of saturation and the
supersaturation limit is
called the _________ and are generally within this
zone.

A

metastable zone width

76
Q

The first step of crystallization is the phase separation, or “birth,” of a new crystal. This step is called ________.

A

nucleation

77
Q

The second step of crystallization is the _____ of these crystals to larger
sizes by the addition of solute molecules from the supersaturated solution. This step is called crystal
________.

A

growth

78
Q

The initial stage of crystallization involves the ________ of a new phase due to the system being in a
condition.

A

spontaneous appearance; non-equilibrium

79
Q

Spontaneous appearance of a new phase is followed by ________ dissolved in
the supersaturated solution, leading to the formation of a
nucleus.

A

aggregation of molecules

80
Q

A ____________ can be defined as the minimum amount of a new phase capable of independent existence. However, the exact nature of nuclei is still unknown.

A

nucleus

81
Q

The birth of these small nuclei in an initially metastable
phase is called __________.

A

nucleation

82
Q

Nucleation may occur spontaneously or be induced
artificially by ____________

A

seeding, agitation, mechanical shock, electric
and magnetic fields, and other external influences.

83
Q

___________ is the generation
of nuclei directly from a
previously crystal-free solution

A

Primary nucleation

84
Q

_______________ takes
place in the presence of
preexisting parent crystals of the
same solute in the solution, which
act as catalysts for further
nucleation

A

Secondary nucleation

85
Q

In pure solutions consisting of only solute and solvent
molecules, nucleation is triggered by the _________ , with the probability of a given
fluctuation occurring being identical over the whole
volume of the system.

A

fluctuations of
solute concentration

86
Q

Homogeneous
nucleation rarely
occurs in practice, but
it forms the ________.

A

basis of nucleation theories

87
Q

The ____________ describes the
homogeneous nucleation process in terms of Gibbs free
energy and a critical cluster size beyond which growth
occurs instantaneously.

A

classical nucleation theory (CNT)

88
Q

According to CNT, ________ give
rise to the appearance of _______ , which continuously form and dissolve in the solution until a
_________ is reached.

A

fluctuations in a metastable phase ; pre-nucleation clusters; critical size

89
Q

Mathematically, homogeneous nucleation is described as
the sum of the free energy change for ________ and the free energy change for the _______.

A

phase transformation (∆Gv); formation of a surface (∆Gs)

90
Q

Because the solid state is more stable than the liquid, the __________ – decreasing the total
free energy.

A

second term (∆Gv) becomes negative

91
Q

By contrast, the ___________
increases the total free energy by an amount proportional to the surface area of the pre-nucleating cluster.

A

first term (∆Gs)

92
Q

Nucleation depends on the competition between a decrease in _____ , which favors growth, and an increase in _____ , which favors dissolution.

A

∆Gv; ∆Gs

93
Q

Small nucleating clusters dissolve unless a _____ is reached,
wherein growth becomes ________ favorable.

A

critical size; energetically

94
Q

At the critical size, rc, d/dr(deltaG) =

A

zero

95
Q

The maximum value of the free energy change is _________.

A

ΔGcrit

96
Q

The growth of clusters is governed by the _____________.

A

Gibbs-Thomson equation

97
Q

We introduce a mathematical term for supersaturation:

A

ln(c/c) = lnS = 2(sigmanu)/(k*T)

98
Q

The GT relationship relates
supersaturation with _________.

A

interfacial diffusion

99
Q

The rate of primary nucleation may
also be empirically expressed using the theory of __________.

A

chemical kinetics

100
Q

Theoretically, the frequency factor A is in the order of_______ nuclei/cm3-s

A

10^30

101
Q

For heterogeneous nucleation, A ≈ ______ nuclei/cm3-s

A

10^25

102
Q

Given the nature of nucleation, a general theory for the prediction of nucleation rate _________.

A

does not exist

103
Q

A model based on a _______ was
found to be satisfactory in explaining most experimental
studies of nucleation kinetics.

A

power-law expression

104
Q

Assumptions to the CNT: Clusters are _______ droplets with uniform ________ and sharp ________.

A

spherical; densities; interfaces

105
Q

Assumptions to the CNT: The molecular arrangement in the crystals’ _______ is identical to the
____________.

A

embryo; macroscopic crystal

106
Q

Assumptions to the CNT: The _________ and ______ of the surface energy is neglected.

A

curvature; temperature dependence

107
Q

Assumptions to the CNT: Cluster growth takes place via ________ addition, while _______ of clusters are ignored.

A

monomer-by-monomer; collisions and break-up

108
Q

Assumptions to the CNT: There is no ___3 ()______ motion.

A

translational, vibrational, or rotational

109
Q

Assumptions to the CNT: Clusters are established _________ at the _______ of supersaturation.

A

instantaneously; onset

110
Q

Assumptions to the CNT:
Nucleation rate is _______ and does not depend on _______
of the sample.

A

time independent; thermal history

111
Q

The clusters are _________. The vapors that might surround them are ideal at __________.

A

incompressible; constant pressure

112
Q

The classical nucleation theory is an _________ of
the nucleation process.

A

oversimplification

113
Q

Other nucleation theories include the _________ and the _________.

A

two-step nucleation
theory; pre-nucleation cluster theoretical pathway

114
Q

Homogeneous nucleation is uncommon in practice
because the presence of foreign particles, such as dust and
dirt, and surfaces, such as container walls and baffles,
induce _________________.

A

heterogeneous nucleation

115
Q

Heterogeneous nucleation occurs because the foreign
particles (or surfaces) decrease the ___________ necessary for nucleation via a reduction of the ________of prenucleation clusters.

A

activation barrier; surface
excess energy

116
Q

Heterogeneous nucleation occurs at _________ than that necessary for homogeneous nucleation.

A

much lower supersaturation

117
Q

__________ happens when crystallization proceeds in the presence of ________ of the
crystallizing solute in a supersaturated solution.

A

Secondary nucleation; parent crystals

118
Q

The parent crystals act as _______ that allow nucleation to occur even at lower supersaturation compared to what is required for primary nucleation.

A

catalysts

119
Q

The secondary nuclei may be from the following:
1. A ______ which allows breeding from a parent crystal
seeded in the solution.

A

seed

120
Q

The secondary nuclei may be from the following:
2. A _________, which may be anything from solid impurities
such as dust or crystalline fragments. Any _______may
become a site for secondary nucleation.

A

crystallite

121
Q
  1. A ________ formed by fluid shear.
    The nucleation occurs along the ______________ between
    the crystal and the solution.
A

solute concentration gradient; boundary layer

122
Q

Once a nucleus reaches critical size and has stabilized, they
begin to grow into macroscopic crystals. This process is
called _________.

A

crystal growth

123
Q

Crystal growth is described by a change in the ________
of the crystal with time.

A

dimension

124
Q

Crystal growth theories generally describe crystals growing in a ________ fashion – meaning a molecule in solution must _______ on a crystal surface.

A

layer-by-layer; desolvate and adsorb

125
Q

There are three possible
sites where a molecule
could attach itself to the
growing crystal: a
___________.

A

terrace, a step, or a kink

126
Q

A _______ is generally a growing crystal surface

A

terrace

127
Q

A _______ is a location where a molecule is attached to both a growing surface layer and a growing step

A

step

128
Q

A __________ is a location where the molecule is attached to three surfaces.

A

kink

129
Q

The general mechanism is described as:
1. Transport of solute molecules from _______ to the crystal surface
2. ______ on the growing crystal surface
3. _______ over the crystal surface
4. Attachment to a ______
5. _____ along a step followed by integration into the growing crystal at a _______ site
6. Diffusion of ______ away from the crystal surface
7. Liberation of ________

A

bulk; Adsorption; Diffusion; step; Diffusion; kink; solvent shell molecules; heat of crystallization

130
Q

One way to measure crystal growth rate is through measurement of the ____________.

A

mass change of the crystal

131
Q

Despite the complex process, we can also express crystal
growth in terms of _________, based on a __________ – a solute
diffuses through a boundary layer and is then incorporated
into the crystal. The rate of growth is based on the distance
moved per unit time in a direction perpendicular to the
surface.

A

rate equations; diffusion model

132
Q

Note that as the solute deposits, two resistances are encountered:
* Resistance to mass transfer from the ________ to crystal surface
* Resistance to the integration of molecules into the ___________

A

bulk liquid; space lattice

133
Q

When a crystalline solid with a particular crystal size
distribution (CSD) is in contact with a saturated solution,
however, the CSD can change with time.

A

Ostwald ripening

134
Q

Ostwald ripening

A

The phenomena in which smaller particles in solution dissolve and deposit on larger particles in order
to reach a more thermodynamically stable state wherein the
surface to area ratio is minimized.

135
Q

_________ refers to the external appearance of a crystal.

A

Crystal habit

136
Q
A
137
Q

The crystal habit (or morphology) is determined by the
relative growth rate of its various crystallographic faces,
with a general rule being that the faces that appear grow the
_________.

A

slowest

138
Q

Many factors influence the overall crystal habit: from the
conditions of crystal growth to possible impurities present
during nucleation, and even the kind of solvent used in the
solution. Generally, crystal habit is strongly affected by:

A
  • Degree of supersaturation
  • Agitation intensity
  • Density and size of crystals
  • Purity of solution
139
Q

Crystal habit can also vary dramatically with the rate of
______ and _______.

A

crystal growth; nucleation

140
Q

In the manufacture of terephthalic acid by _________, the rapid
reaction and high supersaturation
results to a product crystal without
any ________.

A

air oxidation of p-xylene; crystal faces

141
Q

Crystallization of terephthalic acid at slower rates yields a _______.

A

monoclinic
needle

142
Q

______________ may also
be classified by the degree to
which crystal faces are
developed

A

External crystal habit

143
Q

Faces are well- developed due to
uncrowded crystal growth

A

Euhedral

144
Q

Crystals with partially developed faces

A

Subhedral

145
Q

Crystals with undeveloped faces

A

Anhedral

146
Q

Depending on the intended application of the crystalline
material, the solid form is considered a very important
parameter in terms of its performance and _______.

A

processability

147
Q

The crystal habit may affect a product performance in terms of:

A
  • Solubility
  • Product purity
  • Dissolution rate
  • Stability
  • Bioavailability
  • Appearance
148
Q

The crystal habit may affect industry processability in terms of:

A
  • Morphology
  • Flowability
  • Density
  • Particle shape and texture
149
Q

The phenomenon of a chemical species to adopt in more
than one crystalline packing arrangement.

A

Crystal polymorphism

150
Q

When a material crystallizes into a different polymorph,
the _________ of the species remain identical, but
the _________ of the material can be different.

A

chemical nature; physical properties

151
Q

Density, heat capacity, melting point,
optical activity, thermal conductivity, etc.

A

Physical properties

152
Q

Powder properties

A

Compaction and flow

153
Q

According to McCrone (1965): “the number of polymorphs of
a given molecule is proportional to the _______ spent on that compound.”

A

time, money, and experiments

154
Q

A compound with many polymorphs.

A

5-methyl-2-[(2-nitrophenyl)amino]-3-thiopenecabonitrile (ROY)

155
Q

_____________ are crystals
in which the structure contains either a non-stoichiometric or
a stoichiometric amount of solvent in the crystal lattice.

A

Solvates (or hydrates when the solvent is water)

156
Q

Solvates are considered as _________ because of the
inclusion of the solvent molecules in the lattice.

A

“pseudo-polymorphs”

157
Q

Crystallization in polymorphic systems is ruled by a
combination of ___________ and ____________ factors.

A

thermodynamic; kinetic

158
Q

____________ will provide information on relative
stabilities of polymorphs.

A

Thermodynamics

159
Q

__________ will determine which form will be created and for
how long it will survive.

A

Kinetics

160
Q

Glycine form that is stabilized only through confinement (least stable).

A

beta-glycine

161
Q

Glycine form that is stabilized with cooling/evaporation at neutral pH (middle stability).

A

alpha-glycine

162
Q

Glycine form that is stabilized with crystallization at low pH (high stability).

A

gamma-glycine

163
Q

In crystallization processes, two expressions are often
used: crystallization from _________ and crystallization from _________.

A

solution; melts

164
Q

Ulrich, Özoğuz, and Stepanski (1988) suggested that crystallization from solution occurs when _______
effects dominate the process, and crystallization from melt occurs when _________ effects dominate the
phase change.

A

mass transfer; heat transfer

165
Q

Melt crystallization may be applied to the following systems:

A
  • Isomers with close boiling points
  • Azeotropic systems
  • Temperature-sensitive substances
  • Components that tend to polymerize
  • Explosive substances
  • Eutectic systems
  • Solid-solution systems

Ph@rm@ (11 decks)

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