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ORG CHEM LAB > EX5: RECRSYTALLIZATION & SUBLIMATION > Flashcards

EX5: RECRSYTALLIZATION & SUBLIMATION Flashcards

1
Q

also known as fractional crystallization

A

RECRYSTALLIZATION

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2
Q

RECRYSTALLIZATION is also known as

A

fractional crystallization

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3
Q

involves the DISSOLUTION OF THE SOLID in an appropriate solvent AT AN ELEVATED TEMPERATURE and the subsequent RE-FORMATION OF CRYSTALS UPON COOLING, so that any impurities remain in solution

A

RECRYSTALLIZATION

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4
Q

almost all ______ are MORE SOLUBLE in a HOT than in a cold solvent, and solution crystallization takes advantage of this fact

A

SOLIDS

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5
Q

almost all SOLIDS are ________ than in a cold solvent, and solution crystallization takes advantage of this fact

A

MORE SOLUBLE IN HOT SOLVENT

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6
Q

RECRYSTALLIZATION PROCESS

A

Selection of an appropriate solvent
Dissolution of the solid to be purified in the solvent
Decoloration with activated charcoal
Filtration of the hot solution to remove insoluble impurities
Formation of the crystals as it cools
Isolation of the purified crystals by filtration
Drying the crystals

SE DIDEy FInale FOR Isol Dry

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7
Q

MOST CRITICAL STEP in the process: selected to form a product of high purity and in good recovery or yield

A

SELECTION OF AN APPROPRIATE SOLVENT

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8
Q

desired compound should be _______ in the HOT SOLVENT, and ________________ in the COLD SOLVENT

A

SOLUBLE in HOT; INSOLUBLE or NEARLY INSOLUBLE in COLD

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9
Q

__________ should either be INSOLUBLE in the solvent AT ALL TEMPERATURES or must remain at least MODERATELY SOLUBLE in the COLD SOLVENT

A

IMPURITIES

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10
Q

the __________ of the solvent should be LOW enough so that it can readily be removed from the crystals

A

BOILING POINT

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11
Q

the solvent should _____________ with the SUBSTANCE BEING PURIFIED

A

SHOULD NOT REACT CHEMICALLY

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12
Q

what do you call the solvent that DISSOLVES the solute in HOT solution but NOT in the
COLD solution

A

GOOD SOLVENT

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13
Q

what do you call the solvent that DOES NOT DISSOLVE the solute in HOT solution but DISSOLVES in the COLD solution

A

POOR SOLVENT

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14
Q

most ________ dissolves in HOT solvents than in cold ones

A

ORGANIC COMPOUNDS

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15
Q

COMMON ERRORS IN DISSOLUTION

A
  1. too much solvent is used
  2. supersaturated soln
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16
Q

using excessive amounts may decrease recovery

A

TOO MUCH SOLVENT IS USED

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17
Q

what method should be used in putting solvent

A

DROPWISE METHOD

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18
Q

HIGH DEGREE OF MICROPOROSITY; has large surface area

A

ACTIVATED CHARCOAL

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19
Q

it is important to filter the solution while _____ to PREVENT PREMATURE CRYSTALLIZATION during filtration

A

HOT

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20
Q

a ________ or _____________ should be used to minimize crystallization in the funnel

A

SHORT-STEMMED or STEMLESS GLASS FUNNEL

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21
Q

using ___________ will minimize crystallization on the filter

A

FLUTED FILTER PAPER

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22
Q

REDUCE THE TEMPERATURE to induce crystal formation; generally the solution should not be disturbed as it cools, since this also leads to production of small crystals

A

COOLING

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23
Q

CRYSTAL OF THE ORIGINAL SOLID is ADDED to the SOLUTION to INDUCE CRYSTALLIZATION, which may then be QUITE RAPID

A

SEEDING

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24
Q

a GLASS ROD is to RUB the INSIDE SURFACE of the crystallization vessel at or just above the air/solution interface; microscopic
scratches provide sharp edges where crystals may grow

A

SCRATCHING

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25
__________ provide SHARP EDGES where CRYSTALS MAY GROW
MICROSCOPIC SCRATCHES
26
stirring and agitating the solution will INDUCE BUMPING OF CRYSTALS which causes to REFORMATION OF MORE CRYSTALS
STIRRING AND AGITATION
27
during cooling and crystallization, the solution should be protected from _________ by covering the opening with a piece of filter paper, an inverted beaker, or by loosely plugging it with a clean cork
AIRBORNE CONTAMINANTS
28
solution should not be ________ AS IT COOLS, since this also leads to production of small crystals
DISTURBED
29
cool the solution in an ______ to hasten crystal formation
ICE BATH
30
crystals EASILY FORM at a
LOW TEMPERATURE
31
be careful not to use _______ as it MAY FORM SMALL CRYSTALS
TOO LOW TEMPERATURE
32
occasionally the solute will SEPARATE from solution AS AN OIL rather than a solid; this type of separation is UNDESIRABLE FOR PURIFICATION of solutes because the OILS USUALLY CONTAINS SIGNIFICANT AMOUNT OF IMPURITIES
OILING OUT
33
the solid product is isolated by _______ using a Büchner or Hirsch funnel and a clean, dry filter flask or by _________
VACUUM FILTRATION or GRAVITATIONAL FILTRATION
34
used in VACUUM FILTRATION
BUCHNER OR HIRSCH FUNNEL
35
removing the last traces of solvent from the crystalline product may be accomplished by
AIR OR OVEN DRYING (air dry is better)
36
% recovery formula
weight of crystals recovered / weight of the orginal sample x 100
37
the PURITY OF CRYSTALS is usually assessed using ________________, as the presence of the impurities decreases the melting point of the product
MELTING POINT DETERMINATION
38
the PRESENCE OF IMPURITIES _______ the MELTING POINT of the product
DECREASES
39
employed to DETECT ANY SODIUM CHLORIDE IMPURITY LEFT on the purified crystals
SILVER NITRATE TEST
40
indicates presence of NaCl
WHITE PPT or TURBID SOLN
41
SOLID TO GAS
SUBLIMATION
42
GAS TO SOLID
DEPOSITION
43
defined as the DIRECT CONVERSION of a substance from its SOLID PHASE TO ITS GAS PHASE without passing through the liquid phase
SUBLIMATION
44
MOTH BALLS, NAPHTHALENE
SUBLIMATION
45
DRY ICE FORMATION
DEPOSITION
46
sublimation process ENTIRELY RELIES on the ___________________ rather than solid and liquid phases
EQUILIBRIUM BETWEEN SOLID & GAS PHASES
47
where IMPURE SAMPLE IS PLACED
OUTER or LOWER VESSEL
48
where the PURE SOLID is FORMED
INNER or UPPER VESSEL
49
the UPPER VESSEL must be _____ for the pure solids to form on it
COLD
50
DIFF FORMS OF CRYSTALS
* light and feathery crystals * round and scaly crystals * needle-like crystals * blocks of crystals
51
the crystals, deposit, or material OBTAINED WHEN A SUBSTANCE IS HEATED
SUBLIMATE
52
has high vapor pressure, low melting point, and more volatile
SUBLIMATE
53
the solid particle that REMAINED ON THE DISH
RESIDUE
54
has low vapor pressure, high melting point, and less or non-volatile
RESIDUE
55
purification process depends on _____
VOLATILITY
56
less volatile or non-volatile impurities remain as a ______
RESIDUE
57
the process of sublimation is very convenient to apply; however, its application is LIMITED since it CANNOT BE USED for SEPARATING COMPOUNDS that have _______________
SIMILAR VAPOR PRESSURES
58
employed to DIFFERENTIATE the ORGANIC SUBSTANCE FROM the INORGANIC RESIDUE
BARIUM CHLORIDE TEST
59
BaCl2 will react with __________, producing WHITE PPT, thereby identifying the residue from the sublimate
SODIUM SULFATE Na2SO4
60
BaCl2 will react with Na2SO4, producing _______________, thereby identifying the residue from the sublimate
WHITE PPT
61
antifungal and preservative
BENZOIC ACID
62
BENZOIC ACID molecular weight
122.12 g/mol
63
BENZOIC ACID melting point
122-123 C
64
BENZOIC ACID boiling pojnt
249 C
65
BENZOIC ACID synonyms
CARBOXYBENZENE, BENZENE CARBOXYLIC ACID
66
BENZOIC ACID density
1.32 g/cm3
67
toxic to the lungs & nervous system (prolonged exposure may lead to target organ damage)
BENZOIC ACID
68
the crystals will ________ if methylene blue is INCOMPLETELY SEPARATED
REMAIN BLUE
69
the crystals upon the SILVER NITRATE TEST must ___________ to be able to conclude a COMPLETE SEPARATION
MUST NOT YIELD WHITE PPT
70
keratolytic, used to treat acne, seborrhea, corn, calluses and warts
SALICYLIC ACID
71
SALICYLIC ACID mw
138.12 g/mol
72
SALICYLIC ACID melting point
158 C
73
SALICYLIC ACID boiling point
211 C
74
SALICYLIC ACID synonym
2-hydroxybenzoic acid
75
SALICYLIC ACID density
1.44 g/cm3
76
Toxicity: salicylism (through ingestion)
SALICYLIC ACID
77
SEPARATION (SUBLIMATION) COMPOUND - sublimate
SALICYLIC ACID
78
SEPARATION (SUBLIMATION) COMPOUND - residue
SODIUM SULFATE
79
SEPARATION (SUBLIMATION) APPEARANCE - sublimate
NEEDLE-LIKE CRYSTAL
80
SEPARATION (SUBLIMATION) APPEARANCE - residue
AMORPHOUS POWDER
81
SEPARATION (SUBLIMATION) POLARITY - sublimate
non-polar
82
SEPARATION (SUBLIMATION) TYPE - sublimate
ORGANIC
83
SEPARATION (SUBLIMATION) VAPOR PRESSURE - sublimate
8.2 × 10-5 mmHg at 25°C
84
SEPARATION (SUBLIMATION) VAPOR PRESSURE - residue
3.4 × 10-5 mmHg at 25°c
85
SEPARATION (SUBLIMATION) TYPE - residue
INORGANIC
86
SEPARATION (SUBLIMATION) POLARITY - residue
POLAR

ORG CHEM LAB (20 decks)

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