ORGANIC
CHEMISTRY
LAB REPORT 04
EXPERIMENT TITLE:
SUBLIMATION
ABSTRACT
Sublimation
is the transition of solid into a gas phase without passing the liquid phase. Small
samples of unclean solids can be purified by sublimation, or evaporation consolidation.
The imperfect solid is heated on a hot surface, evaporation and condensation (solidifying)
on a cold surface. Once on
the cold surface, the purified compound can be carefully extracted collected,
leaving the impurities behind the hot surface. Sublimation is useful a
purification technique if the impurities are essentially non-volatile and a
desirable substance its melting point has a vapor pressure of at least a few Torre.
Sublimation is best used on small sample sizes since the product loss in
transfer and collection is small.
INTRODUCTION
Sublimation
is the transition from the solid phase to the gas phase without passing through
an intermediate liquid phase. This endothermic phase transition occurs at
temperatures and pressures below the triple point. The term
"sublimation" only applies to physical changes of state and not to
the transformation of a solid into a gas during a chemical reaction. The opposite
process of sublimation where a gas undergoes a phase change into solid form is
called deposition or DE sublimation.
Sublimation
is widely used to separate volatile components from non-volatile components. As
such, it is a useful preparation technique for the recovery of compounds that
can be emptied at reasonable temperatures, atmospheric pressure or reduced
pressure. The temperature at which a sublimate is observed in a particular
system is often called the sublimation temperature, but it is useless for
comparative purposes unless the variables such as pressure, size, and geometry
of the sublimation apparatus are standardized. The list of substances that can
be sublimation includes aromatic hydrocarbon hydrocarbons, benzoic acid,
salicylic acid, camphor, saccharin, quinine, cholesterol, pallet and stearic
acids, acetylsalicylic acid and atropine. Despite its success, sublimation has
limited application and extraction dependence on the vapor pressure of the analyses
at a given temperature and pressure, and the nature of the matrix, make it
difficult to optimize trace analysis.
OBJECTIVES
1) Purifying small amount of solid organic
substances
MATERIALS AND METHOD
MATERIALS
·
Naphthalene
·
Small
dry beaker
·
Round
bottom flask
·
Watch
glass
·
Ice
METHODS
1.
1g of
dry crude material (naphthalene) was placed in a small beaker.
2.
A round
bottom flask which is smaller than the largest diameter of the beaker
containing ice, was put on the top of the beaker
3.
Beaker
was heated gently.
4.
Heating
was stop after the material vaporized and the vapor reached the cold surface of
the round bottom flask where it cools and condenses as fine crystal.
5.
The
system was led to cool for a while and collect the pure crystals formed on dry
clean watch glass.
6.
Product
was weighted and percentage yield of the pure compound was calculated.
RESULTS
Mass
of the impure sample = 1g
Mass
of the weighing paper = 1.03 g
Mass
of the naphthalene crystals + weighing paper = 1.95
1st
time:
Mass
of the pure sample = 1.95 g- 1.03 g= 0.92 g
Percentage
yield of the pure compound = 0.92/1.0 X100 % = 92 %
2nd
time:
Mass
of paper + naphthalene extract = 1.79
Mass
of pure sample = 1.79 – 1.03 = 0.76
Percentage
yield of pure sample= 0.76/1.0 x 100% = 76%
DISCUSSION
This
experiment conducted to study the sublimation of naphthalene. Naphthalene is a compound which
has formula of C10H8. The aim of this
experiment was to observe the phase changes of naphthalene and also
the ability of naphthalene to sublime and so deposit.
Naphthalene crystals disappear with time because they undergo the
method of sublimation within which solids directly change to gas
without probing liquid state. Sublimation is a purification method of
organic compounds was a way or methods to clean the useful
substances from impurities so as to get the required pure
substances.
The impure
naphthalene was heated in a beaker covered with round bottom flask filled
with ice cubes. Once the material vaporizes and the vapor passes up into the
cold surface of the round bottom flask where it cools
and condenses as fine crystals which called as sublimate. The sublimate was
collected afterwards for computing percentage recovery. If we want to collect
maximum amount of crystals the system was
fixed and the processes are repeated .This
percentage recovery was affected thanks to some possible errors.
Sources of errors would come with excess heat and another error would
be the innate difficulty of extracting all of the crystals, which
might affect the percent recovery.
QUESTIONS
1.
Define
the following terms
a.
Evaporation
Evaporation
is the process of which, element or compound transition from its liquid state
to its gaseous state below the temperature at that it boils
b.
Sublimation
Sublimation
is the process of which, element or compound transition from solid phase to
gaseous phase without passing through the liquid phase
2.
Naphthalene,
C10H8 is insoluble in water but sublimes easily when
heated. How could you separate a mixture of naphthalene and NaCl?
Naphthalene will sublime easily but common
salt won't sublime. Heat the mixture of Naphthalene and NaCl.
Naphthalene will sublime into a gas. Place a cooled surface above the fumes.
The cooled surface cause the Naphthalene vapors to return to the solid phase.
But the NaCl will remain within the original container due
to it'll be unaffected by the heating.
APENDIX
Figure 1; heat water bath with naphthalene beaker with ice.
Figure 2; crystals made from naphthalene
REFERENCES
1. Joaquín Isac-García,
... Henar Martínez-García, in Experimental Organic Chemistry, 2016
2. Donald
M. Mattox, in Handbook of Physical Vapor Deposition (PVD) Processing (Second
Edition), 2010
3. Wilfred
L.F. Armarego, in Purification of Laboratory Chemicals (Eighth Edition), 2017
Post a Comment