INTRODUCTION:
The world has become aware
of environmental issue
in recent years. Synthetic compounds are highly
polluting, hazardous and much more costly. Researchers are working
in the field of natural products extensively
as they are less hazardous, low cost, easily available, and eco-friendly1.
Colours of substances make the world a wonderful place.
Because of the colours and structures; flowers, plants,
animals, and minerals show
their unique characters. There are various organic and inorganic
compounds responsible
for natural colours.
Some of the organic compounds i.e. flavonoids,
flavonols, acylated flavonoids, anthocyanins, glucosylated acylated anthocyanin, quinines, imines, polymethines, napthaquinones, anthraquinonoids, indigoids; dihydropyrans diarylmethanes carotene etc. imparts colours to the flower. Among them anthocyanidins and flavones are main.
Flavones:
Flavones as well as flavonols and their glycosides continue
to attract attention of biologist, because of their presence in many
food plants, and in commonly available medicinal plants.
Currently, most attention
is being given to their anti- inflammatory and antioxidative activities
Flavones are soluble in water and alcohol
and
can be extracted by chopping and macerating the plant material, soaking it for
a few minutes in hot water or rubbing with
alcohol2.
These
are yellow pigments which occur
in plant kingdom either in the free state or
as glycosides
or associated
with
tannins.
These are also known
as the anthoxanthins. Chemically
they are hydroxylated derivative of flavone
(2- phenyl chromen-4-one)3.
Anthocyanins
The other pigment present in plants is anthocyanin
and
substituted anthocyanin. These are the water soluble pigments
and
are largely responsible for attractive colours of flowers, leaves, fruits etc4.
Chemically, anthocyanins are glycosides
and their aglycones, i.e. the sugar free pigments are known
as the anthocyanidins. The various anthocyanins were shown to possess the same carbon skeleton and
differed only in the nature of substituent groups. The fundamental nucleus is 2-
phenyl chromenylium
chloride or (flavylium chloride).
Indicators:
Indicator is a substance used to locate the end point in a titration process,
for example phenolphthalein, methylen
blue, methyl red methyl orange etc are indicators used in acid base
titrations.
Classification
of
indicators:
Indicators are
classified as
an external (added externally during the titration) and internal or self indicator is one which is not added externally but one of
the titrating solutions behaves as an indicator. They are further classified as redox indicator used in redox titrations, precipitating
indicator/adsorption indicators used in
precipitation titration, complexing indicator used in
complexation
titration and acid
base or pH indicators.
pH Indicators
The pH indicators
are
substances whose solutions change color due to changes in pH. These are also called
acid- base indicators or neutralization indicator. They are usually
weak
acids or bases, but their conjugate
base or acid forms have different colors due to differences in their absorption
spectra. Indicators are complicate organic
weak
acids or bases with
complicated
structures. For simplicity, we
represent a
general indicator by the formula HIn for acidic indicators and
In OH for basic indicator.
MATERIALS
AND METHODS:
Titration:
Acid-base titration:
In the chemistry lab it is sometimes
necessary to experimentally determine the
concentration of an acid solution or a base solution.
A procedure for making this kind of
determination is called an acid-base titration.
In this procedure, a
solution of known concentration, called the standard solution, is used to neutralize a precisely measured volume of
the solution of unknown
concentration to which one or two drops of an appropriate indicator
have been added. If the solution of unknown
concentration is acidic, a standard base solution is added to the acid solution until it is neutralized.
If
the solution of unknown
concentration is basic,
a standard acid solution is added to the base solution
until it is neutralized5,6.
When carrying out an acid-base titration
a sudden change
in color of the indicator signals
that
neutralization has
occurred. At this point, the number of
hydronium ions7,8 from the acid is equal to the number of hydroxide ions
from the base.
The point at which this occurs is called the end point
of the titration.
Materials and Reagents required Synthetic
Indicators:
Phenolphthalein
Methyl red
Methyl orange
Natural indicator obtained from fresh vegetable
Procedure
Preparation of indicator
100
gm of chopped beetrrot was added to 100ml of solution
containing Ethanol – Hydrochloric acid (v/v ratio 99:1) and Ethanol – water
(v/v ratio 1: 1) for 45 minutes, after allowing the beaker to cool for 15
minutes, boiled beetroot were squashed and the liquid was filtered. The residue
was squeezed again and the liquid has evaporated to get a highly concentrated
portion of the indicator. The extract was preserved in tightly closed container
and stored away from the sun light.
Titration I
Strong acid Vs
Strong base (Hydrochloric acid and sodium hydroxide)
5
ml sodium hydroxide of was pipette out into a clean conical flask and 3 drops
phenolphthalein indicator was added and titrated against Sodium hydroxide taken
in the burette. Appearance of permanent pale pink colour
is the end point. The titration must be repeated for concordant values. Same
procedure can be followed with different indicators including methylred, methyl orange and natural indicator obtained from
beetroot. The titration was carried in triplicate and standard deviation was
calculated from the results. Same procedure was carried for strong acid – strong
base (Hydrochloric acid
d m y y k S u b
Sodium hydroxide), and Weak
acid weak base (Acetic acid – Ammonium hydroxide). Strong acid- weak base
(Hydrochloric acid – Ammonium hydroxide).
RESULTS
AND DISCUSSION:
Titration I Strong
Acid – Strong Base
Titrations
Titration of Strong acid (Hydrochloric
acid) with strong base (Sodium Hydroxide) using synthetic indicators like
phenolphthalein, methyl red, methyl orange and beet root extract (table-1).
Statistical
analysis was made with the values obtained from the titration. The volume of titrand needed for the neutralization is recorded and
calculated for standard deviation and standard error. Specific end point was
found for each indicator used in the experiment. The mixture of solution turns
an colorless solution to pink when using phenolphthalein as indicator solution,
pink color to yellow in color when using both methyl red and methyl orange as
an indicator separately where as pink color turns colorless solution when crude
methanolic extract of beetroot was used as an acid
base indicator9,10.
Each
sets of color change have its unique range of pH specific against the
indicators used. The neutralization reaction found occurs in particular pH
range like pH 6, 7 and 10 against phenolphthalein, methyl red, methyl orange
and beetroot extract respectively. The mean and standard deviation shows
closeness to the accuracy of the results (table-1).
Titration II Weak acid Vs
Strong base
With
reference to titration II, the volume of sodium hydroxide needed for the
neutralization of acetic acid was recorded and calculated for standard
deviation and standard error. Specific end point was found for each indicator
used in the experiment. The mixture of solution turns an colorless solution to
pink when using phenolphthalein as indicator solution, pink color to yellow in
color when using both methyl red, methyl orange turns orange to yellow, where
as pink color turns colorless solution when crude methanolic
extract of beetroot was used as an acid base indicator. Each sets of color
change have its unique range of pH specific against the indicators used. The
neutralization reaction found occurs in particular pH range like pH 6, 6, 6 and
10 against phenolphthalein, methyl red, methyl orange and beetroot extract
respectively. The mean and standard deviation shows closeness to the accuracy
of the results (table-2).
Titration III - Weak acid Vs Weak base
Titration
III was done for weak acid and weak base. The volume of ammonium hydroxide
needed for the neutralization of acetic acid was recorded and calculated for
standard deviation and standard error. Specific end point was found for each
indicator used in the experiment. The mixture of solution turns an colorless
solution to pink when using phenolphthalein as indicator solution, pink color
to yellow in color when using both methyl red, methyl orange turns orange to
yellow, where as pink color turns colorless solution when crude methanolic extract of beetroot was used as an acid base
indicator. Each sets of color change have its unique range of pH specific
against the indicators used. The neutralization reaction found occurs in
particular pH range like pH 9, 6, 6 and 10 against phenolphthalein, methyl red,
methyl orange and beetroot extract respectively. The mean and standard
deviation shows closeness to the accuracy of the results (table-3).