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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
Q

__________ provide SHARP EDGES where CRYSTALS MAY GROW

A

MICROSCOPIC SCRATCHES

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26
Q

stirring and agitating the solution will INDUCE BUMPING OF CRYSTALS which causes to REFORMATION OF MORE CRYSTALS

A

STIRRING AND AGITATION

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27
Q

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

A

AIRBORNE CONTAMINANTS

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28
Q

solution should not be ________ AS IT COOLS, since this also leads to production of small crystals

A

DISTURBED

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29
Q

cool the solution in an ______ to hasten crystal formation

A

ICE BATH

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30
Q

crystals EASILY FORM at a

A

LOW TEMPERATURE

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31
Q

be careful not to use _______ as it MAY FORM SMALL CRYSTALS

A

TOO LOW TEMPERATURE

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32
Q

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

A

OILING OUT

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33
Q

the solid product is isolated by _______ using a Büchner or Hirsch funnel and a clean, dry filter flask or by _________

A

VACUUM FILTRATION or GRAVITATIONAL FILTRATION

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34
Q

used in VACUUM FILTRATION

A

BUCHNER OR HIRSCH FUNNEL

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35
Q

removing the last traces of solvent from the crystalline product may be accomplished by

A

AIR OR OVEN DRYING (air dry is better)

36
Q

% recovery formula

A

weight of crystals recovered / weight of the orginal sample x 100

37
Q

the PURITY OF CRYSTALS is usually assessed using ________________, as the presence of the impurities decreases the melting point of the product

A

MELTING POINT DETERMINATION

38
Q

the PRESENCE OF IMPURITIES _______ the MELTING POINT of the product

39
Q

employed to DETECT ANY SODIUM CHLORIDE IMPURITY LEFT on the purified crystals

A

SILVER NITRATE TEST

40
Q

indicates presence of NaCl

A

WHITE PPT or TURBID SOLN

41
Q

SOLID TO GAS

A

SUBLIMATION

42
Q

GAS TO SOLID

A

DEPOSITION

43
Q

defined as the DIRECT CONVERSION of a substance from its SOLID PHASE TO ITS GAS PHASE without passing through the liquid phase

A

SUBLIMATION

44
Q

MOTH BALLS, NAPHTHALENE

A

SUBLIMATION

45
Q

DRY ICE FORMATION

A

DEPOSITION

46
Q

sublimation process ENTIRELY RELIES on the ___________________ rather than solid and liquid phases

A

EQUILIBRIUM BETWEEN SOLID & GAS PHASES

47
Q

where IMPURE SAMPLE IS PLACED

A

OUTER or LOWER VESSEL

48
Q

where the PURE SOLID is FORMED

A

INNER or UPPER VESSEL

49
Q

the UPPER VESSEL must be _____ for the pure solids to form on it

50
Q

DIFF FORMS OF CRYSTALS

A
  • light and feathery crystals
  • round and scaly crystals
  • needle-like crystals
  • blocks of crystals
51
Q

the crystals, deposit, or material OBTAINED WHEN A SUBSTANCE IS HEATED

52
Q

has high vapor pressure, low melting point, and more volatile

53
Q

the solid particle that REMAINED ON THE DISH

54
Q

has low vapor pressure, high melting point, and less or non-volatile

55
Q

purification process depends on _____

A

VOLATILITY

56
Q

less volatile or non-volatile impurities remain as a ______

57
Q

the process of sublimation is very convenient to apply; however, its application is LIMITED since it CANNOT BE USED for SEPARATING COMPOUNDS that have _______________

A

SIMILAR VAPOR PRESSURES

58
Q

employed to DIFFERENTIATE the
ORGANIC SUBSTANCE FROM the INORGANIC RESIDUE

A

BARIUM CHLORIDE TEST

59
Q

BaCl2 will react with __________, producing WHITE PPT, thereby identifying the residue from the sublimate

A

SODIUM SULFATE
Na2SO4

60
Q

BaCl2 will react with Na2SO4, producing _______________, thereby identifying the residue from the sublimate

61
Q

antifungal and preservative

A

BENZOIC ACID

62
Q

BENZOIC ACID molecular weight

A

122.12 g/mol

63
Q

BENZOIC ACID melting point

64
Q

BENZOIC ACID boiling pojnt

65
Q

BENZOIC ACID synonyms

A

CARBOXYBENZENE, BENZENE CARBOXYLIC ACID

66
Q

BENZOIC ACID density

A

1.32 g/cm3

67
Q

toxic to the lungs & nervous system (prolonged exposure may lead to target
organ damage)

A

BENZOIC ACID

68
Q

the crystals will ________ if methylene blue is INCOMPLETELY SEPARATED

A

REMAIN BLUE

69
Q

the crystals upon the SILVER NITRATE TEST
must ___________ to be able to conclude a COMPLETE SEPARATION

A

MUST NOT YIELD WHITE PPT

70
Q

keratolytic, used to treat acne, seborrhea, corn, calluses and warts

A

SALICYLIC ACID

71
Q

SALICYLIC ACID mw

A

138.12 g/mol

72
Q

SALICYLIC ACID melting point

73
Q

SALICYLIC ACID boiling point

74
Q

SALICYLIC ACID synonym

A

2-hydroxybenzoic acid

75
Q

SALICYLIC ACID density

A

1.44 g/cm3

76
Q

Toxicity: salicylism (through ingestion)

A

SALICYLIC ACID

77
Q

SEPARATION (SUBLIMATION)
COMPOUND - sublimate

A

SALICYLIC ACID

78
Q

SEPARATION (SUBLIMATION)
COMPOUND - residue

A

SODIUM SULFATE

79
Q

SEPARATION (SUBLIMATION)
APPEARANCE - sublimate

A

NEEDLE-LIKE CRYSTAL

80
Q

SEPARATION (SUBLIMATION)
APPEARANCE - residue

A

AMORPHOUS POWDER

81
Q

SEPARATION (SUBLIMATION)
POLARITY - sublimate

82
Q

SEPARATION (SUBLIMATION)
TYPE - sublimate

83
Q

SEPARATION (SUBLIMATION)
VAPOR PRESSURE - sublimate

A

8.2 × 10-5 mmHg at 25°C

84
Q

SEPARATION (SUBLIMATION)
VAPOR PRESSURE - residue

A

3.4 × 10-5 mmHg at 25°c

85
Q

SEPARATION (SUBLIMATION)
TYPE - residue

86
Q

SEPARATION (SUBLIMATION)
POLARITY - residue

ORG CHEM LAB (20 decks)

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