Recrystallization

Topics: Solvent, Solubility, Ethanol Pages: 10 (880 words) Published: September 3, 2014
Laboratory Experiment Report
Title of Experiment: Recrystallization

Aim:
To determine suitable recrystallization solvents for four organic compounds through their solubility characteristics. To purify sample of organic compounds that is solids by recrystallization at room temperature. To determine the melting point of the substance to characterize it and calculate % recovery.

Material and Method: AS outlined in the lab manual , Page 6-9,Page 20. Recrystallization: Using a hot plate, a mixture of impure phenanthrene (2.2g) and charcoal was dissolved in boiling ethanol (minimum amount) in a 125 mL Erlenmeyer flask. The saturated solution was filtered while it remained hot and then was allowed to cool. The purer substance crystallized out of solution and then was filtered off with suction and washed with small portions of cold solvent, and recrystallized from ethanol to give phenanthrene as white powder ( 1.4g, ), m.p. 101-2 °C Result:

See proforma following.
PART A : The table of solvents, with b.p.s and polarities
Solvent
Structure
B.P. °C
Hildebrand
Constant(H)
water

100.0
23.4
methanol

65
14.6
ethanol

78.5
12.5
acetone

56.2
9.8
toluene

110.6
8.9
Petroleum
Spirit
(b.p.60-70 °C)
Mainly hexane

69
7.3

PART B : Choosing a Solvent
Determine suitable recrystallization solvents for the following compounds:

(a) Phenanthrene

Solvent
Soluble
cold
Soluble
hot (1ml)
Soluble
Hot (4ml)
Crystals
when
cooled
water
x
x
x
-
methanol
x
x

x
ethanol
x

acetone

-
-
-
toluene

-
-
-
hexane
x
x

x

(b)m-dinitrobenzene
Solvent
Soluble
cold
Soluble
hot (1ml)
Soluble
Hot (4ml)
Crystals
when
cooled
water
x
x
x
-
methanol
x

-

ethanol
x

-

acetone

-
-
-
toluene

-
-
-
hexane
x
x
x
-

(c) Acetanilide
Solvent
Soluble
cold
Soluble
hot (1ml)
Soluble
Hot (4ml)
Crystals
when
cooled
water
x

methanol

-
-
x
ethanol

-
-
x
acetone

-
-
x
toluene
x

x

hexane
x
x
x
x

(d) pentaerythritol
Solvent
Soluble
cold
Soluble
hot (1ml)
Soluble
Hot (4ml)
Crystals
when
cooled
water
x

methanol
x
x
x
x
ethanol
x
x
x
x
acetone
x
x
x
x
toluene
x
x
x
x
hexane
x
x
x
x

PART C: Recrystallization and melting point
Calculate the percent recovered using the following written formula and determine the melting point of your recrystallized phenanthrene.

Phenanthrene Data
Sample
Physical appearance
Melting point
Impure
Brown powder
94 °C
Pure
White Crystals

Literature Value
(cite source)
White Crystals
99-101
Amount of Phenanthrene used initially____________________g
Amount of Phenanthrene recovered______________________g
Percentage recovery of Phenanthrene (% Recovered) = 100 X
Weight of phenanthrene obtained after recrystallization

Weight of benzoic acid before recrystallization
=
=
=

Colour and Crystalline form of the product:

Discussion:
1. For a given compound, what is the solubility behavior in a solvent of similar polarity to the compound? To understand the recrystallization process, solubility behavior must first be considered. It is often stated that "like dissolves like". More correctly, it should be stated that, "compounds having similar structural features will be soluble in one another". Some obvious structural features that may affect solubility include polarity and the ability to hydrogen bond. For example, a non-polar compound would be expected to be soluble in non-polar solvents. For known compounds it is useful to consider the structure of the compound when choosing a recrystallization solvent. 2. What happens when the solvent’s polarity differs more from that of the compound? If the solvent’s polarity differs more from that of the compound, the compound will be less soluble in the solvent. For example, Acetanilide is more polar, it is non-soluble in cold water,...
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