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Sublimation and Melting Point Determination
Adolfo, Angela Angela Nicole G., G., Alcaraz, Frances Jillian Jillian F. F. Aliman, Stephanie Stephanie T., T., Astor, Astor, Jashmin D. Bauzon, Franchesca D., a!ral, Danica "ose G.
Department of Pharmacy, Faculty of Pharmacy University of Santo Tomas
ABSTA!T The sample of !enzoic acid #as purified through su!limation. su!limation. This process occurs if the $apor pressure of a su!stance is greater than the atmospheric pressure. The product o!tained after the heating process is called a su!limate, and it is in the form of needle% li&e cr'stals. For the melting point determination, the su!limated #as grinded into a fine po#der and a small tu!e #as pressed into it. (ure !enzoic acid #as also pressed into the tu!e for comparati$e reasons. The t#o capillar' tu!es together #ith the thermometer #as immersed in an oil !ath and #as heated. The oil !ath #as used since it is a!le to #ith #ithst stan and d temp temper erat atur ures es e)ce e)ceed edin ing g 1** 1** ℃ and and is ther theref efor ore e a!le a!le to meas measur ure e more more accuratel'.
than the pure compound. "#T$DU!T"$#
n this e)periment, su!limation is
Su!limation is a process of direct
used to purif' the crude form !enzoic acid
$aporization of solids #ithout passing
#hich is impure. t has amino compounds
through the li+uid state. Also, it #ill occur
#hich must !e remo$ed !ecause it
in solids onl' if the $apor pressure is
contains phen'l and !enz'l compounds
greater than the atmospheric pressure at
that can affect the product. -oreo$er,
the melting point. The $aporization%
there is the process of melting point
solidification c'cle can !e used as a
determination to ascertain the identit' and
purification process #hich is applica!le
purit' of an un&o#n compound that
onl' if the impurities are non%$olatile or
should !e done together #ith su!limation.
ha$e significantl' lo#er $apor pressure
The follo#ing are the o!ecti$es to !e
/
achie$ed !' the group0
tu!ing. (ure !enzoic acid #as also #eighed and #ell%pac&ed in capillar'
1 to use the process of su!limation to
tu!es to ser$e as a standard of reference.
purif' the impure !enzoic acid
The capillar' tu!es #ere then attached to
/ to determine and compare the melting
a thermometer using a thread, the closed
points of the su!limate and the pure
end attached to the mercur' !ul! of the
!enzoic acid
thermometer. An oil !ath setup #as then
2 to calculate the percentage reco$er' of
assem!led, #here the capillar' tu!es #ill
the !enzoic acid
!e immersed, and then it #as put into heat.
M%T&$D$'$()
The
students
recorded
the
temperature at #hich !oth compounds started to melt and the temperature at
First a su!limation setup #as used to
#hich !oth has completel' melted.
purif' the !enzoic acid, place 3g of impure !enzoic acid in an e$aporating
%SU'TS A#D D"S!USS"$#
dish co$ered #ith a perforated filter paper and a pre%#eighed in$erted #atch glass,
Table *+ Data and esults
fastened it using a mas&ing tape to ser$e
5eight of impure
as a co$er. 4eat it on a hot plate for 13
!enzoic acid 5eight of #atch
g
glass 6 su!limate 5eight of #atch
-. g
glass 7empt' 5eight of su!limate
-/+ g
minutes, #hile
da!!ing
a
moistened
tissue paper on top of the #atch glass. Allo# it to cool after to room temperature, then collect the su!limate found in the #atch glass and perforated filter paper,
0+ g
#eigh it in the same #eighing scale used
(ercentage
to #eighing the pre%#eighed #atch glass
reco$er' -elting point of
*01
!enzoic acid
2.℃
used
in
percentage
the
setup.
reco$er'
alculate from
the
the data
collected. For the determination of melting point, the su!limate #as pac&ed into a capillar' tu!e, and to ensure that it is tightl' pac&ed together the capillar' tu!e #as dropped for se$eral times in a glass
Table 2+ Melting Points
2
Temperature
Temperatur
1
e/
Su!limate
/1℃
//℃
8
Standard
19℃
//℃
the standard in order to compare their melting points. The standard !egan to melt at /1℃ and it completel' melted at
!A'!U'AT"$#S
//℃ . The sample !egan to melt at 19 ℃ and it completel' melted at // ℃ .
mass of su!limate : reco$er' ; ) 1** mass of sample
!$#!'US"$# Su!limation method is $er'
; ) 1**
0.5 g 5 g
; 1*: Discussion
effecti$e for purif'ing su!stances in small +uantities !ecause there
The !enzoic acid 7the su!limate #as
for the percentage reco$er'. This ma'!e
heated on a hot plate, and solidified into
!ecause of the small amount of cr'stals
cr'stalline forms after appro)imatel' 13
or su!limate collected #ithin the process
minutes. This #as due to the $apor of the
of su!limation. =onger time for the
!enzoic acid acting upon the heat and
process to occur is needed so enough
proceeding into the su!limation phase.
and more su!limate #ill !e gathered.
The *.3 g of the !enzoic acid that #as collected from the pre$ious 3.* g of
n melting point determination,
!enzoic acid sample #ill !e used to
e)periment sho#s that the su!limate is
compute for the percentage reco$er' of
still not that pure !ut is close to !eing a
the su!stance, #hich resulted in 1*:.
pure !enzoic acid, !ecause the range of
The colorless needle%li&e cr'stals #ere
/> indicates a pure su!stance !ut the
later grinded on to !e a!le to insert it into
collected su!limate has a range of 8>.
the capillar' tu!es. The grinded cr'stals
Factors that might affect the e)periment
are then inserted into the capillar' tu!e
included loss $apor due to poor
attached to a thermometer, #hich #as
su!limation set%up or inaccurate
later su!ected to a hot oil !ath #hich #as
measurements of the su!stances.
used to melt the su!stance together #ith
%F%%#!%S
The University of North Carolina at Chapel Hill (2014). Melting and sublimation. Retrievedfrom https0??cssac.unc.edu?programs?learning% center?"esources?Stud'?Guides?hemistr':/*1*/?-elting:/*and:/*Su!limation
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The 5ired hemist 7/*1@. Determination of melting point. "etrie$ed from http0??###.#iredchemist.com?chemistr'?instructional?la!orator'%tutorials?determination% of%melting%point
D$!UM%#TAT"$#
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