Download Recrystallisation Benzoic Acid Determination Melting Point

Producing pure substances is a very important process,
especially in the pharmaceutical industry. Separating
insoluble solids from solvents is easily achieved using a
simple technique called filtration. Soluble solids again
are easily separated from solvents by evaporation, and
chromatography is used to separate a mixture of liquids. But
what happens when we have two soluble solids that we want
to separate? In this lesson we will look at recrystallisation, a
commonly-used process in the pharmaceutical industry.
Fig.1 Filtration to remove insoluble impurities
Benzoic Acid
Fig.1 Finding the melting
point of benzoic acid
Beaker containing benzoic acid dissolved in
minimum amount of boiling water
Filter funnel with fluted filter paper to
speed up the filtrarion process. Insoluble
impurities left behind as residue
Melting Point
Thermometer
Benzoic acid crystals
and
Recrystallisation
of its
Determination
of
Benzoic Acid
and
of
Recrystallisation
tapped sharply against the
desk causing the crystals to
fall to the sealed end. When
about 3 mm of crystals are
in the base of the tube it is
placed in the oil bath. The
temperature at which the
sample begins to melt and
the temperature at which
it is completely melted are
recorded.
Aluminium block
To double check your
Producing pure substances is a very important process,
Fig.1 Filtration to remove insoluble impurities
result, mix a sample of
What is recrystallisation?
benzoic acid with some
especially in the pharmaceutical industry. Separating
pure benzoic acid. If both
Recrystallisation is a very important purification technique, purifying
Conical flask with hot concentrated
Bunsen burner
are pure benzoic acid the
insoluble
solids
from
solvents
isused
easily achieved usingbenzoic
a acid solution which still contains
substances
by removing
unwanted
by-products.
It is also
melting
will remain
to manufacture the correct crystal size and shape of a material.
soluble impurities
Beaker containing benzoic
acidpoint
dissolved
in
simple
technique
called
fi
ltration.
Soluble
solids
again
the same but if the sample
These factors can have a very significant impact on how a
minimum amount of boiling
water
is not
pure benzoic acid
medicine acts when taken by a patient. The same principles and
are ofeasily
separated
solvents
then the melting point will
techniques
recrystallisation
can be applied from
both on a laboratory
and by evaporation, and
be lowered.
industry scale.
chromatography is used to separate a mixture of liquids. But
Fig.2 After that
cooling, we
the remaining
what
whenbehind
we have two soluble solids
wantsolution is filtered off
How do I know I have a pure substance?
What
arehappens
the principles
recrystallisation?
Pure
benzoic
acid cystals
The melting Filter
point of funnel
a substance
is not
the exact
pointpaper
at which to
it melts
with
fluted
filter
to separate? In this lesson we will look at recrystallisation,
a
but rather the range of temperatures from when the samples starts to melt
The process depends on two principles; the fact that substances tend
speed
up
the
filtrarion
process.
Insoluble
until it has completely melted. The greater the range the more impurities
in the
pharmaceutical
industry.
to becommonly-used
more soluble in a hot solventprocess
than in cold solvent,
and that
each
Büchner funnel
solute tends to behave as though it were alone in the solvent.
How is crystallisation used in industry?
How
do I know
what solvent to use?
What
is recrystallisation?
Using the correct solvent is a very important part of the process. The
solute
must be insoluble in the solvent
room temperature,
andpurifi
as the cation technique, purifying
Recrystallisation
is a atvery
important
temperature of the solvent increases, the solubility of the solute also
substances
by that
removing
by-products.
It is also used
increases.
It is also important
the impuritiesunwanted
present are soluble
in
the solvent
at room temperature
and insoluble
at higher
temperatures.
to manufacture
the
correct
crystal
size and shape of a material.
An excellent
showinghave
this process
is benzoic
acid cant impact on how a
These substance
factorsfor can
a very
signifi
(C 6 H 5COOH). A molecular crystal rather than an ionic crystal, shown
medicine
actsof 122
when
takenacidby
a patient.
by its
low melting point
°C, benzoic
is used
as an anti- The same principles and
microbial
agent and is of
found
in toothpastes, mouthwashes,
techniques
recrystallisation
can becosmetics
applied both on a laboratory and
and deodorants.
Büchner flask
Water containing soluble impurities
industry scale.
Impure benzoic acid contains the impurities phthalic acid and
benzylbenzoate. If the impure sample is dissolved in a minimal volume of
hot solvent – in this case boiling water – and filtered to remove insoluble
impurities, the resulting solution will contain dissolved benzoic acid as
well as dissolved impurities.
present. A range
of less thanleft
1 °Cbehind
indicates aas
pure
substance.
impurities
residue
The use of crystallisation in the pharmaceutical industry is an important
process for controlling the physical properties, yield and purity of an
ConicalIngredient
flask with
hot
concentrated
Active Pharmaceutical
(API).
Many
production processes
use crystallisation
in theacid
final stage
of manufacture
achieve
these
benzoic
solution
which tostill
contains
targets. Recent advances in crystallisation process monitoring allow for
soluble
impurities
a better understanding of the process. These advances allow crystals
with specific physical properties, for example particle size and shape,
to be created. It is possible to produce crystals of varying particle size,
shape and form polymorphs of the same substance, but only one will be
suitable for drug development and manufacture.
D
Glaxo
comp
the s
a lea
infect
nervo
The
comm
qualit
to live
World
manu
Curra
the a
facilit
in de
chem
The C
site w
autom
with P
We a
GSK’
Type
Canc
Glaxo
Dung
Dubli
In industry, the way an API is filtered and dried can have a very significant
impact on the physical properties of the material.
How can we check the purity of
Calculating
percentage
yield
our substance?
Fig.2 After cooling, the
remainingthe
solution
is filtered
off
What are the principles behind
After the crystallisation process the amount of sample will have been
A pure substance has a fi xed melting point while an impure substance
reduced as impurities have been removed. To calculate how much of the
Upon cooling, the benzoic acid crystals comes out of solution as its
melts over a wide range of temperatures and at a lower temperature
recrystallisation?
Purepure
benzoic
acid cystals
substance was present in the initial impure sample, the percentage
solubiluty in the solvent decreases. The impurities will remain in solution
than the pure substance. The melting points of almost all substances
and can be filtered off.
yield is calculated.
are available in tables.
The process depends on two principles; the fact that substances tend
It is very important when carrying out this experiment that rubber gloves
To check the melting point place a few crystals of the sample on an
to be
moreorganic
soluble
in a can
hotbesolvent
than in
andwhich
thathaseach
are worn,
because
substances
absorbed through
the cold solvent,
aluminium block
a thermometer inserted. Use a hot plate
skin,solute
and as well,
goggles
should
be
worn
to
protect
your
eyes
from
hot
heatsolvent.
the block slowly. Watch the crystals carefully and note the
tends to behave as though it were alone intothe
liquids which may spray out from the flask.
temperature at which they begin to melt and the temperature at which
they have all melted. Compare this value with the value found on the
bottle of pure substance. Another method of checking the melting point of
crystals is to use a narrow capillary tube in an oil bath. The capillary tube
has one end open and the other end sealed. The open end is pressed
into fine crystals of the substance and the turned upside down and
How do I know what solvent to use?
Percentage yield = Mass of pure sample (after recrystallisation)
x 100
Mass of impure sample (before recrystallisation)
Büchner funnel
The percentage yield is a good indicator of the purity of the initial
sample. A high percentage yield implies a low concentration of
impurities, whereas a low percentage yield indicates a sample with a
lot of impurities.
Using the correct solvent is a very important part of the process. The
solute must be insoluble in the solvent at room temperature, and as the
temperature of the solvent increases, the solubility of the solute also
increases. It is also important that the impurities present are soluble in
the solvent at room temperature and insoluble at higher temperatures.
An excellent substance for showing this process is benzoic acid
(C 6 H 5COOH). A molecular crystal rather than an ionic crystal, shown
by its low melting point of 122 °C, benzoic acid is used as an antimicrobial agent and is found in toothpastes, mouthwashes, cosmetics
and deodorants.
Impure benzoic acid contains the impurities phthalic acid and
benzylbenzoate. If the impure sample is dissolved in a minimal volume of
hot solvent – in this case boiling water – and filtered to remove insoluble
impurities, the resulting solution will contain dissolved benzoic acid as
well as dissolved impurities.
Upon cooling, the benzoic acid crystals comes out of solution as its
solubiluty in the solvent decreases. The impurities will remain in solution
and can be filtered off.
It is very important when carrying out this experiment that rubber gloves
are worn, because organic substances can be absorbed through the
skin, and as well, goggles should be worn to protect your eyes from hot
liquids which may spray out from the flask.
Büchner flask
Water containing soluble impurities
How can we check the purity of
our substance?
A pure substance has a fi xed melting point while an impure substance
melts over a wide range of temperatures and at a lower temperature
than the pure substance. The melting points of almost all substances
are available in tables.
To check the melting point place a few crystals of the sample on an
aluminium block which has a thermometer inserted. Use a hot plate
to heat the block slowly. Watch the crystals carefully and note the
temperature at which they begin to melt and the temperature at which
they have all melted. Compare this value with the value found on the
bottle of pure substance. Another method of checking the melting point of
crystals is to use a narrow capillary tube in an oil bath. The capillary tube
has one end open and the other end sealed. The open end is pressed
into fine crystals of the substance and the turned upside down and
You
Glax
www
of its
Determination
Melting Point
���
����������������������
������� ��������������
Melting Point
Producing pure substances is a very important process,
especially in the pharmaceutical industry. Separating
insoluble solids from solvents is easily achieved using a
simple technique called filtration. Soluble solids again
are easily separated from solvents by evaporation, and
chromatography is used to separate a mixture of liquids. But
what happens when we have two soluble solids that we want
to separate? In this lesson we will look at recrystallisation, a
commonly-used process in the pharmaceutical industry.
and
of
Benzoic Acid
��
Determination
of its
and
Recrystallisation
Fig.1 Filtration to remove insoluble impurities
Fig.1 Finding the melting
point of benzoic acid
Beaker containing benzoic acid dissolved in
minimum amount of boiling water
Filter funnel with fluted filter paper to
speed up the filtrarion process. Insoluble
impurities left behind as residue
Thermometer
Benzoic acid crystals
tapped sharply against the
desk causing the crystals to
fall to the sealed end. When
about 3 mm of crystals are
in the base of the tube it is
placed in the oil bath. The
temperature at which the
sample begins to melt and
the temperature at which
it is completely melted are
recorded.
Aluminium block
To double check your
tapped sharply against the
result, mix a sample of
Fig.1
the melting
What
is Finding
recrystallisation?
desk causing the crystals to
benzoic acid with some
point
of
benzoic
acid
pure benzoic acid. If both
Recrystallisation is a very important purification technique, purifying
fall to the sealed end. When
Conical flask with hot concentrated
Bunsen burner
are pure benzoic acid the
substances by removing unwanted by-products. It is also used
benzoic acid solution which still contains
about 3 mm of crystals are
melting point will remain
to manufacture the correct Thermometer
crystal size and shape of a material.
soluble impurities
the same but if the sample
These factors can have a very significant impact on how in
a the base of the tube it is
is not pure benzoic acid
medicine acts when taken by a patient. The same principles and
placed
in
the
oil
bath.
The
then the melting point will
techniques of recrystallisation can be applied both on a laboratory and
be lowered.
industry scale.
temperature at which the
sample begins to melt and
Fig.2 After cooling, the remaining solution is filtered off
How do I know I have a pure substance?
What are the principles behind
the temperature at which
Benzoic acid crystals
recrystallisation?
Pure benzoic acid cystals
The melting point of a substance is not the exact point at which it melts
it is completely melted
are
but rather the range of temperatures from when the samples starts to melt
The process depends on two principles; the fact that substances tend
recorded.
until it has completely melted. The greater the range the more impurities
to be more soluble in a hot solvent than in cold solvent, and that each
GlaxoSmithKline ispresent.
a leading
Büchner funnel
A range ofresearch-based
less than 1 °C indicates a pharmaceutical
pure substance.
solute tends
to behaveblock
as though it were alone in the solvent.
Aluminium
company committed to excellence and innovation. We are
To double check your
the second largest How
life science
company in
the in
world
and have
result, mix a sample of
is crystallisation
used
industry?
How do I know what solvent to use?
a leadership position
inof four
major
therapeutic
areasis an– important
antibenzoic acid with some
The use
crystallisation
in the
pharmaceutical industry
Using the correct solvent is a very important part of the process. The
process for controlling the physical
properties, yield
and central
purity of an
infectives, gastrointestinal/metabolic,
respiratory
and
pure benzoic acid. If both
solute must be insoluble in the solvent at room temperature, and as the
Active Pharmaceutical Ingredient (API). Many production processes
temperature
of the solvent
Bunsen
burnerincreases, the solubility of the solute also
nervous system. use crystallisation in the final stage of manufacture to achieve these
are pure benzoic acid the
increases. It is also important that the impurities present are soluble in
targets. Recent advances in crystallisation process monitoring allow for
the solvent at room temperature and insoluble at higher temperatures.melting point will remain
allow crystals
better understanding
of the process. is
These
advances
The source of our a competitive
advantage
the
energy
and
with specific physical properties, for example particle size and shape,
An excellent substance for showing this process is benzoic acid
the same but if the sample
Büchner flask
commitment of ourtoemployees.
Our tomission
is toof varying
improve
the
be created. It is possible
produce crystals
particle
size,
(C 6 H 5COOH). A molecular crystal rather than an ionic crystal, shown
is not pure benzoic acid
same
substance,
only oneand
will be
and form polymorphs
by its low melting point of 122 °C, benzoic acid is used as an antiquality of human lifeshape
to enable
people oftothedo
more,
feelbutbetter
Water containing soluble impurities
suitable for drug development and manufacture.
microbial agent and is found in toothpastes, mouthwashes, cosmetics
then the melting point will
to live longer.
and deodorants.
In industry, the way an API is filtered and dried can have a very significant
be lowered.
impact on the physical properties of the material.
Impure benzoic acid contains the impurities phthalic acid and
World-wide
we
employ
over 110,000 people and have 80
benzylbenzoate. If the impure sample is dissolved in a minimal volume of
How can we check the purity of
hot solvent – in this case boiling water – and filtered to remove insoluble
manufacturing sites in 37 countries. At our Cork Site in
Calculating the percentage yield
impurities, the resulting solution will contain dissolved benzoic acid as
our substance?
How
do
I know I have a pure substance?
Currabinny, which was established in 1975, we manufacture
well
as dissolved
impurities.
After the crystallisation process the amount of sample will have been
A pure substance has a fi xed melting point while an impure substance
active
ingredients
ofasmedical
compounds.
Currabinny
reduced
impurities have
been removed. To Our
calculate
how much of the
Upon cooling, the benzoic acid crystals comes out of solution as its
melts over a wide range of temperatures and atthe
a lower
temperature
The
melting
point
of
a
substance
is
not
the
exact
point
at
which
it
melts
pure500
substance
was present
in the of
initial
impure sample,
the percentage
solubiluty in the solvent decreases. The impurities will remain in solution
than the pure substance. The melting points of almost
all substances
facility
employs over
people,
many
whom
are engaged
yield is calculated.
and
canrather
be filtered
off. range of temperatures from when the samples
are available in
tables. to melt
but
the
starts
in development chemistry, analytical and quality chemistry and
It is
very important
when carrying outmelted.
this experiment
rubber gloves
To the
checkmore
the melting
point place a few crystals of the sample on an
until
it has completely
Thethat
greater
the range
impurities
Percentage yield = Mass of pure sample (after recrystallisation)
x 100
chemical
and
Mass of impure sample (before recrystallisation)
are worn, because organic substances can be absorbed through the
block which has a thermometer inserted.
Use a hot
plateprocess engineering.
present.
Agoggles
rangeshould
of less
than
1 °Cyour
indicates
a purealuminium
skin,
and as well,
be worn
to protect
eyes from hot
tosubstance.
heat the block slowly. Watch the crystals carefully and note the
percentage yield
is a good
of the introduction
purity of the initial
liquids which may spray out from the flask.
temperature at which they begin to melt and the The
temperature
which
Corkat facility
is The
a strategic
global
newindicator
product
sample. A high percentage yield implies a low concentration of
they have all melted. Compare this value with the value found on the
site
within
GSK’s
manufacturing
network.
We
have
highly
impurities, whereas a low percentage yield indicates a a
sample
with a
bottle of pure substance. Another method of checking the melting point of
lot of impurities.
crystals is to use a narrow capillary tube in an oil bath.
The capillary tube
How is crystallisation used in industry?
automated
manufacturing
facility, as well as an R&D Pilot Plant
has one end open and the other end sealed. The open end is pressed
with
Pilot
Plant
into fine crystals of the substance and the turned
upside
down
and Laboratories on site.
The use of crystallisation in the pharmaceutical industry
is an important
process for controlling the physical properties, yield and purity of an
We are currently the primary production site for a number of
Active Pharmaceutical Ingredient (API). Many production processes
GSK’s top selling drugs which treat illnesses such as depression,
use crystallisation in the final stage of manufacture to achieve these
Type 2 Diabetes, Congestive Heart Failure, Ulcers, HIV, Ovarian
targets. Recent advances in crystallisation process monitoring allow for
Cancer, Breast Cancer, Parkinson’s Disease and Arthritis.
a better understanding of the process. These advances allow crystals
GlaxoSmithKline also has a manufacturing and R&D facility in
with specific physical properties, for example particle size and shape,
Dungarvan, Co. Waterford and sales and marketing functions in
to be created. It is possible to produce crystals of varying particle size,
Dublin. GSK currently employs over 1,400 in Ireland.
shape and form polymorphs of the same substance, but only one will be
suitable for drug development and manufacture.
In industry, the way an API is filtered and dried can have a very significant
impact on the physical properties of the material.
Calculating the percentage yield
After the crystallisation process the amount of sample will have been
reduced as impurities have been removed. To calculate how much of the
pure substance was present in the initial impure sample, the percentage
yield is calculated.
Percentage yield = Mass of pure sample (after recrystallisation)
x 100
Mass of impure sample (before recrystallisation)
The percentage yield is a good indicator of the purity of the initial
sample. A high percentage yield implies a low concentration of
impurities, whereas a low percentage yield indicates a sample with a
lot of impurities.
You can find out more about the work of
GlaxoSmithKline at www.gsk.com,
www.gsk.com/worldwide/ie.htm or at www.sta.ie
Glaxo
comp
the s
a lea
infect
nervo
The
comm
qualit
to live
World
manu
Curra
the a
facilit
in de
chem
The C
site w
autom
with P
We a
GSK’
Type
Canc
Glaxo
Dung
Dubli
You
Glax
www
Producing pure substances is a very important process,
especially in the pharmaceutical industry. Separating
insoluble solids from solvents is easily achieved using a
simple technique called filtration. Soluble solids again
are easily separated from solvents by evaporation, and
chromatography is used to separate a mixture of liquids. But
what happens when we have two soluble solids that we want
to separate? In this lesson we will look at recrystallisation, a
commonly-used process in the pharmaceutical industry.
Fig.1 Filtration to remove insoluble impurities
Beaker containing benzoic acid dissolved in
minimum amount of boiling water
Thermometer
Benzoic acid crystals
tapped sharply against the
desk causing the crystals to
fall to the sealed end. When
about 3 mm of crystals are
in the base of the tube it is
placed in the oil bath. The
temperature at which the
sample begins to melt and
the temperature at which
it is completely melted are
recorded.
Aluminium block
To double check your
result, mix a sample of
benzoic acid with some
pure benzoic acid. If both
Conical flask with hot concentrated
Bunsen burner
are pure benzoic acid the
benzoic acid solution which still contains
melting point will remain
soluble impurities
the same but if the sample
Recrystallisation of benzoic acid and determination isofnot
its pure
melting
point.
benzoic
acid
then the melting point will
be lowered.
and at the same
Boil about 100 cm3 deionised water in a suitable beaker
Syllabus
Reference
What
is recrystallisation?
Practical Activities
Recrystallisation is a very important purification technique, purifying
substances by removing unwanted by-products. It is also used
to manufacture the correct crystal size and shape of a material.
These
have Carbon
a very signifi
cant impact on how a
Unitfactors
7.2 – can
Planar
compounds
medicine acts when taken by a patient. The same principles and
techniques of recrystallisation can be applied both on a laboratory and
industry scale.
Leaving Certificate Chemistry
Mandatory Experiment – Leaving Certificate
Junior Certificate Science
Section 2A7 – Water and solutions
What are the principles behind
recrystallisation?
Benzoic Acid
Fig.1 Finding the melting
point of benzoic acid
Filter funnel with fluted filter paper to
speed up the filtrarion process. Insoluble
impurities left behind as residue
Melting Point
and
Recrystallisation
of its
Determination
of
Benzoic Acid
and
of
Recrystallisation
time place a conical flask with about the same volume of boiling water
I know
I have
a place
pure substance?
on a hot plate. Into the How
neck do
of this
conical
flask
a fluted filter paper
melting
point ofwater.
a substance
the exact
point atin
which
melts
and wet the filter paperThe
with
boiling
Theis not
boiling
water
theitconical
but rather the range of temperatures from when the samples starts to melt
keeps everything warmuntil
and
stops
premature
recrystallisation.
it has completely melted. The greater the range the more impurities
Fig.2 After cooling, the remaining solution is filtered off
Pure benzoic acid cystals
The process depends on two principles; the fact that substances tend
to be more soluble in a hot solvent than in cold solvent, and that each
solute tends to behave as though it were alone in the solvent.
How do I know what solvent to use?
Using the correct solvent is a very important part of the process. The
solute must be insoluble in the solvent at room temperature, and as the
temperature of the solvent increases, the solubility of the solute also
increases. It is also important that the impurities present are soluble in
the solvent at room temperature and insoluble at higher temperatures.
Learning Objectives
On completing this section, the student will be able to:
An excellent substance for showing this process is benzoic acid
A molecular crystal
rather than an ionic
shown
(C 6 H 5COOH).
• Recognise
the importance
ofcrystal,
the recrystallisation
process
by its low melting point of 122 °C, benzoic acid is used as an antimicrobial agent and is found in toothpastes, mouthwashes, cosmetics
• Understand the principles behind recrystallisation
and deodorants.
Büchner funnel
present. A range of less than 1 °C indicates a pure substance.
Dissolve 1 gram of impure benzoic acid in the minimum amount of boiling
water and leave it on theHow
hot plate.
Empty the boiling
from the conical
is crystallisation
usedwater
in industry?
flask and replace the flThe
askuseonof crystallisation
the hot plate.
Immediately
filteris an
the
benzoic
in the pharmaceutical
industry
important
process for
controlling
the physical
properties,
yield
and purityform
of an on
acid solution into the conical
flask
in small
amounts.
If any
crystals
Active Pharmaceutical Ingredient (API). Many production processes
the paper use tiny amounts
of boilingin water
dissolve
them.
use crystallisation
the final to
stage
of manufacture
to This
achieveprocess
these
targets.
Recent advances
in crystallisation
process
monitoring
allow for
will have removed all the
insoluble
impurities
from the
benzoic
acid.
a better understanding of the process. These advances allow crystals
with specific physical properties, for example particle size and shape,
Büchner flask
The filtrate is then poured
intoIt isa possible
warmto beaker
andof the
water
gently
to be created.
produce crystals
varying
particle size,
substance,
onlyside
one will
form polymorphs
evaporated
until tracesshape
of and
crystals
beginof the
to same
appear
on but
the
ofbe the
Water containing
soluble impurities
suitable for drug development and manufacture.
beaker. At this point you have a hot saturated solution of benzoic acid
In industry, the way an API is filtered and dried can have a very significant
so when the solution impact
is cooled,
crystals
of of
benzoic
acid will come out
on the physical
properties
the material.
Impure •
benzoic
acid contains
the impurities yield
phthalicofacid
and
Calculate
the
percentage
a
sample
after
recrystallisation
benzylbenzoate. If the impure sample is dissolved in a minimal volume of
solution. Cool the solution by placing the beaker in an ice bath – the
How can we check the purityofof
hot solvent – in this case boiling water – and filtered to remove insoluble
• the
Outline
role
recrystallisation
in industry
lower the temperature the
more benzoic
acid will come
out of solution and
Calculating
the percentage
yield
impurities,
resulting the
solution
will of
contain
dissolved benzoic acid
as
our substance?
well as dissolved impurities.
theangreater
your yield After
will the
be.crystallisation
If the crystals
don’t
form
immediately
they
process the
amount
of sample
will have been
A pure substance has a fi xed melting point while
impure substance
•
Measure
the
melting
point
of
crystals
using
the
outlined
procedure
reduced as impurities have been removed. To calculate how much of the
Upon cooling, the benzoic acid crystals comes out of solution as its
melts over a wide range of temperatures and at a lower temperature
can
be
encouraged
by
scraping
the
inside
of
the
fl
ask
with
a
glass
rod.
pure substance was present in the initial impure sample, the percentage
solubiluty in the solvent decreases. The impurities will remain in solution
than the pure substance. The melting points of almost all substances
is calculated.
Remember that in any yield
purifi
cation process you are going to lose some of
and can•
be fiIdentify
ltered off. crystals using melting point data from
aretables.
available in tables.
Mass of pure
sample (after
recrystallisation)
theofsubstance
want.
Filteryieldoff
crystals
using
vacuumx 100
filtration
It is very important when carrying out this experiment that rubber gloves
To check the melting point place a few crystals
the sample on you
an
Percentage
= these
Mass of impure sample (before recrystallisation)
are worn, because organic substances can be absorbed through the
aluminium block which has a thermometer inserted. Use a hot plate
if possible. Any soluble impurities that
are in the solution will still be fully
skin, and as well, goggles should be worn to protect your eyes from hot
to heat the block slowly. Watch the crystals carefully and note the
The percentage
a good
indicator
of the purity
the initial
liquids which may spray out from the flask.
temperature at which they begin to melt and soluble
the temperature
at which
in the
cold water
and so yield
theyis will
pass
through
the of
filter
paper.
sample. A high percentage yield implies a low concentration of
they have all melted. Compare this value with the value found on the
Finally
wash
the
crystals
using
tiny
amounts
of
ice
cold
water
to
impurities, whereas a low percentage yield indicates a sample remove
with a
bottle of pure substance. Another method of checking the melting point of
lot of impurities.
crystals is to use a narrow capillary tube in an oil
bath.
The traces
capillary tube
the
last
of the impurities
from their surface. The fact that the water
General Learning Points
has one end open and the other end sealed. The open end is pressed
is
ice
cold
means
that
it
will dissolve the minimum amount of benzoic acid.
into fine crystals of the substance and the turned upside down and
Dry the crystals on a filter paper. Weigh the crystals and calculate your
• Different separation techniques are used depending on nature of
percentage yield.
solutes and solvents.
•
Filtration can be used to separate insoluble solids from solvents.
•
Evaporation is used to separate soluble solids form solvents.
•
Recrystallisation is used to separate soluble solutes from a mixture of
them in solution.
•
Benzoic acid is used as a microbial agent in toothpastes,
mouthwashes, cosmetics and deodorants.
True or False
Indicate whether the following are true (T) or false (F) by
drawing a circle around T or F.
(a) Separation is used to separate two insoluble solids.
T F
Melting points are calculated to identify substances and to verify
purity of samples.
(b) Recrystallisation is a purifying technique.
T F
(c) An impure substance has a fixed melting point.
T F
•
Recrystallisation is widely used in the pharmaceutical industry to
control physical properties, yield and purity of Active Pharmaceutical
Ingredients.
(d) Organic substances tend to be less soluble in a hot solvent
than in a cold solvent.
T F
•
When choosing what solvent to use, remember more-polar
compounds require polar solvents, where less-polar compounds
require less polar solvents.
(e) A range of 1 °C in melting point of a substance indicates a
pure substance.
T F
(f) Benzoic acid is an ionic crystal due to its high melting point.
T F
(g) Polymorphs are substances with similar molecular
composition but varying crystal structure.
T F
(h) A saturated solution is one which contains more
solvent than solute.
T F
(i) The percentage yield is the mass of the pure sample divided
by the mass of the initial sample.
T F
(j) Recrystallisation is used to produce crystals of specific size
and shape.
T F
•
Check your answers to these questions on www.sta.ie
D
Glaxo
comp
the s
a lea
infect
nervo
The
comm
qualit
to live
World
manu
Curra
the a
facilit
in de
chem
The C
site w
autom
with P
We a
GSK’
Type
Canc
Glaxo
Dung
Dubli
You
Glax
www
Determination
of its
Benzoic Acid
and
of
Recrystallisation
Melting Point
���
����������������������
������� ��������������
��
mental Monitoring
Producing pure substances is a very important process,
especially in the pharmaceutical industry. Separating
insoluble solids from solvents is easily achieved using a
simple technique called filtration. Soluble solids again
are easily separated from solvents by evaporation, and
chromatography is used to separate a mixture of liquids. But
what happens when we have two soluble solids that we want
to separate? In this lesson we will look at recrystallisation, a
commonly-used process in the pharmaceutical industry.
Fig.1 Filtration to remove insoluble impurities
Fig.1 Finding the melting
point of benzoic acid
Beaker containing benzoic acid dissolved in
minimum amount of boiling water
Thermometer
Benzoic acid crystals
Filter funnel with fluted filter paper to
speed up the filtrarion process. Insoluble
impurities left behind as residue
Examination
Questions
What
is recrystallisation?
Junior Certificate 2005, Technology - Higher
potential dividers)
Aluminium block
To double check your
result, mix a sample of
benzoic acid with some
pure benzoic acid. If both
Conical flask with hot concentrated
Bunsen burner
are in
pure1800
benzoicprovided
acid the
• The
invention
of the battery by Alessandro Volta
benzoic acid solution
which still
contains
melting point will remain
soluble impurities
curious experimenters with a source of steady
electric
the same
but if the current
sample
not pure much
benzoic of
acid
whose properties they explored. During the 19th iscentury
the
then the melting point will
basic theory of electricity was developed and many
applications of
be lowered.
Did You Know?
Recrystallisation is a very important purification technique, purifying
substances by removing unwanted by-products. It is also used
to manufacture the correct crystal size and shape of a material.
These
factors
have a 2
very significant impact on how a
Section
B,can
Question
medicine acts when taken by a patient. The same principles and
(concerning
the design
function
of two different
techniques
of recrystallisation
can beand
applied
both on a laboratory
and
industry
scale.C, Question 4
Section
tapped sharply against the
desk causing the crystals to
fall to the sealed end. When
about 3 mm of crystals are
in the base of the tube it is
placed in the oil bath. The
temperature at which the
sample begins to melt and
the temperature at which
it is completely melted are
recorded.
electricity were invented: electromagnet (1820), electric motor (1821),
(concerning robotics, remote control, sensor feedback
in relation to the
Fig.2 After cooling, the remaining solution is filtered off
theory of electricity generation
(1831),
electric
light (1878),
first power
How do I know
I have
a pure
substance?
What are the principles behind
Mars Lander)
recrystallisation?
Pure benzoic acid cystals
station (1879), first hydroelectric
station
(1882),
first
alternating
The melting point ofpower
a substance
is not the
exact point
at which
it melts
but rather the range of temperatures from when the samples starts to melt
The process depends on two principles; the fact that substances tend
current generator (1888),
electricity
distribution
system
(1893),
electric
until it has completely melted. The greater the range the more impurities
toJunior
be more soluble
in a hot
solvent 2004,
than in cold
solvent, and that each
Certifi
cate
Technology
- Higher
Büchner funnel
A rangemachine
of less than 1(1903).
°C indicatesAll
a pure
substance.
vacuum cleaner andpresent.
washing
these
devices are
solute tends to behave as though it were alone in the solvent.
classed as electric.
A student is required to produce a circuit which will turn on a water pump
How is crystallisation used in industry?
whendo
low
water what
levelssolvent
are detected
by a sensor.
How
I know
to use?
• The invention of the diode
in 1904 could be described as the beginning
The use of crystallisation in the pharmaceutical industry is an important
Thethe
components
below part
areofavailable
Using
correct solvent islisted
a very important
the process.to
Theconstruct the circuit.
process
for controlling
the physical
properties,
and purity of an
of electronics. Unlike
wires,
electric
lights
and yield
electromagnets,
solute
must be
insoluble in
the solvent at room
temperature,
andResistor
as the
LED
Sensor
Transistor,
Resistor
2K2,
330R, Motor (pump),
Active Pharmaceutical Ingredient (API). Many production processes
temperature of the solvent increases, the solubility of the solute also
diodes conducts electricity
in one
direction
only
and their
operation
use
crystallisation
in
the
fi
nal
stage
of
manufacture
to
achieve these
Variable
resistor,
battery
increases.
It is also
important 9V
that the
impurities present are soluble in
targets.
Recent advances
in crystallisation
monitoring Another
allow for
cannot be adequately
explained
except
in terms process
of electrons.
the solvent at room temperature and insoluble at higher temperatures.
a better understanding of the process. These advances allow crystals
development along with
thespecifi
same
lines,properties,
the triode,
enables
weak
signals
c
physical
for
example
particle
size
and
shape,
An
excellent
substance
for
showing
this
process
is
benzoic
acid
Büchner
flask
1. Using the sensor and the variable resistor, sketch the circuit diagram for
to bevacuum
created. It is
possible
to produce
crystals
of varying
size,as
(C 6 H 5COOH). A molecular crystal rather than an ionic crystal, shown
to be amplified. These
tube
diodes
and
triodes
(or particle
‘valves’
inisthis
shape and form polymorphs of the same substance, but only one will be
by itsthe
low potential
melting pointdivider
of 122 °C,required
benzoic acid
usedcircuit.
as an antiWater containing
soluble
impurities
they
were
called) were
theforbuilding
blocks
electronics for about fifty
suitable
drug development
andof
manufacture.
microbial
agent
and
is
found
in
toothpastes,
mouthwashes,
cosmetics
2. Name and explain your choice of material for the sensor.
and deodorants.
years.
In industry, the way an API is filtered and dried can have a very significant
3. Explain why a variable resistor is used in the potential divider.
impact on the physical properties of the material.
Impure benzoic acid contains the impurities phthalic acid and
4. IndicateIfclearly
onin athe
variable
benzylbenzoate.
the impure which
sample is pins
dissolved
minimal
volume ofresistor should be used in
• ofSolid-state semiconductor devices began to replace valves in the
How can we check the purity
hot solvent – in this case boiling water – and filtered to remove insoluble
the potential divider.
1950s—crystal diodes
at first and
transistors
some
years later. In the
Calculating
the
percentage
yield
impurities, the resulting solution will contain dissolved benzoic acid as
our substance?
well as dissolved impurities.
first integrated
came
onthe
the
market
andwill
inhave
1972
the
After thecircuits
crystallisation
process
amount
of sample
been
A pure substance has a fi xed melting point while 1960s
an impurethe
substance
reduced as impurities
have been
To calculate how much of the
Upon cooling, the benzoic acid crystals comes out of solution as its
melts over a wide range of temperatures and atfiarst
lower
temperature
commercial
microprocessor
chip
wasremoved.
released.
Junior Certificate 2001, Technology - Higher
solubiluty in the solvent decreases. The impurities will remain in solution
and can be filtered off.
than the pure substance. The melting points of almost all substances
lot of impurities.
2001 Junior Certificate Technology HigherhasLevel
one end open and the other end sealed. The open end is pressed
• Transistors are the active components in many ‘transistorised’ devices
into fine crystals of the substance and the turned upside down and
The sketch shows a circuit for a high temperature alarm.
(i) Identify the components ‘X’ any ‘Y’
State the purpose of component ‘Y’ in the circuit.
S1
+9 V
Z
X
R
Y
such as radios, tape recorders, etc. Increasingly they are integrated
into more complex ‘chips’. The transistor is the solid state successor
to the triode valve and following its invention it gradually replaced the
vacuum tube in most applications. The invention is usually attributed
to William Shockley, John Bardeen and Walter Brattain who in 1947
produced the first practical transistor device. However similar devices
had been described in 1928 and 1934 but it seems that they were not
manufactured. In contrast to the triode, the transistor is a solid device
and its invention marked the beginning of solid-state physics.Today
transistors are the basic subunits in most integrated circuits (ICs or
‘chips’) including microprocessors.
0V
Why is a transistor used in this circuit?
How can the cathode of the LED be correctly identified?
(ii) If the maximum permitted current for the LED is 0.02 A, show how to
calculate the value of the resistor ‘R’ required for the circuit.
Which of the following values should be used for resistor ‘R’?
270 Ω, 330 Ω, 390 Ω, 470 Ω, 560 Ω,
The fourth band in a resistor is either silver or gold. What does the
colour of this band indicate?
(iii) Name and sketch the symbol for the component which should be
located at ‘Z’.
For further examples of past paper questions
check www.sta.ie
The
comm
qualit
to live
World
manu
Curra
the a
facilit
in de
chem
The C
site w
autom
with P
We a
GSK’
Type
Canc
Glaxo
Dung
Dubli
pure substance was present in the initial impure sample, the percentage
yield is calculated.
are available in tables.
Section B, Question 2
• Although the distinction between electric and electronic devices is not
It is very important when carrying out this experiment that rubber gloves
To check the melting point place a few crystals of the sample on an
Percentage yield = Mass of pure sample (after recrystallisation)
100
(concerning
the
design
and
operation
of
a
temperature
alarm:
an
sharp, the word electronic
is nowadays
usually reserved for xdevices
Mass of impure sample (before recrystallisation)
are worn, because organic substances can be absorbed through the
aluminium block which has a thermometer inserted. Use a hot plate
incomplete
circuit
diagram
students
were
expected
to the crystals carefully
skin,
and as well, goggles
should
be worn to was
protect given
your eyesand
from hot
to heat
the block
slowly. Watch
andoperation
note the
whose
depends on solid-state semiconductors. On this
The percentage yield is a good indicator of the purity of the initial
liquids which may spray out from the flask.
temperature at which they begin to melt and the temperature at which
complete it and explain how it functioned.)
basis
an ordinary
electric
‘electric’
but
it could
argued that
sample. lamp
A high is
percentage
yield
implies
a lowbe
concentration
of
they have all melted. Compare this value with the
value found
on the
impurities, whereas a low percentage yield indicates a sample with a
bottle of pure substance. Another method of checking
the melting
point
a CFL
lamp
isof‘electronic’.
crystals is to use a narrow capillary tube in an oil bath. The capillary tube
Glaxo
comp
the s
a lea
infect
nervo
Revise the Terms
Can you recall the meaning of these terms? Reviewing the
terminology is a powerful aid for recall and retention.
Electricity; electric circuit; current; voltage; battery; switch;
automatic; sensor; component; thermostat; bimetallic strip;
temperature; pressure; humidity; potential divider; in series;
resistor; resistance; electronic; thermistor; LDR; calibrate; speaker;
microphone; electric motor; electric generator; transducer; volt;
millivolt; computer; operating system; computer network; ad hoc
network; mote; wireless communication; pH probe; chemical
sensor
Check the Glossary of Terms for this lesson at www.sta.ie
You
Glax
www