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Maryam
khalil
Hifza
iqbal
Tanzeela
mujahid
Farheen
fazal
Ifrah
fahim

DEFINITION:
“It is a substance which is used to indicate the end point or completion of a reaction
by it’s colour change.”
TYPES: Indicators are of two types –
1. natural e.g. turmeric, litmus, china rose and red cabbage
2. artificial. E.g. Ph indicators, redox indicators, adsorption indicator etc
ACID BASE INDICATORS:
“Indicators are substances that are used to test whether a substance is weakly acidic
or basic or neutral in nature. They change their color when added to a solution
containing an acidic or a basic substance.”
Or
“Substances whose solutions change color due to changes in ph. These are
called acid-base indicators. They are usually weak acids or bases, but their
conjugate base or acid forms have different colors due to differences in their
absorption spectra”.

PH INDICATOR:
A pH indicator is a halochromic chemical
compound added in small amounts to a solution so
the pH (acidity or basicity) of the solution or end
point of titration can be determined visually by color
change.
1.Methyl yellow:
ph range: 2.9-4.0
In alkaline solution: it imparts a yellow color .If acid is slowly
added, the solution remains yellow until all the alkali has been
neutralized, where upon the color suddenly changes to red.
Use:
In titration:
The common application of indicators is the detection of end
points of weak base vs strong acid .titration.

2. Phenolphthalein:
Ph range: 8.3- 10.0
It is organic weak base ph indicator.
in acidic solution it remains color less but turns pink to red as the solution
becomes alkaline.
Use:
In titration:
Phenolphthalein is an organic compound used as a laboratory
reagent and pH indicator.
It is use as indicator in weak acid vs strong base titration
Other uses:
Phenolphthalein exerts laxative effects by stimulating the intestinal mucosa
and constricting smooth muscles. However, phenolphthalein is no longer
used as a laxative due to the suspected carcinogenicity of this compound.

3.Methyl red:
it is an ph indicator that turns red in acidic solution.
Ph range: 4.8 - 6.0
Uses:
as indicator in strong acid vs. strong base titration.
Principle:
a pH indicator is a chemical detector for hydronium ions (H3O+) or hydrogen
ions (H+) in the titration.
Application:
pH indicators are frequently employed in titrations in analytical chemistry
and biology to determine the extent of a chemical reaction.
https://en.wikipedia.org/wiki/PH_indicator#Precise_pH_measurement.

“ A redox indicator is an indicator compound that changes color at specific
potential differences.”
OR
“Is a chemical compound that undergoes a color change as it goes from its
oxidized form to its reduced form.”
Redox indicators are ph independent
Principle:
Based on an oxidation-reduction reaction between analyte and
titrant
EXAMPLES:
Redox visual indicators are of two types.
 Self indicator e.g. kMno4
 external indicator e.g. L3Fe(CN)6
Use :
in redox titration

 The choice of an indicator in an acid/base titration actually depends on the strength
of acids and bases involved, ph of indicator, and how well the colors can be
distinguished by the eyes.
 If the difference in volume is small between the equivalence and end points, then the
indicator can be used.
 For a strong acid and a strong base titration (e.g. Hcl and NaoH) methyl orange is a
suitable indicator for this titration.
 Methyl orange changes color over a ph range of 3.2 - 4.4. At ph of 4.4, methyl
orange gives a full color change, indicating the equivalence point. Methyl orange
gives color change very close to the equivalence point, with an error of less than
0.1%. Methyl red (ph range of 4.8 - 6.0) is also suitable for strong acid and strong
base titrations.
 For a weak acid and a strong base (e.g. Acetic or ethanoic acid and NaoH) A suitable
indicator is phenolphthalein. The ph of the mixture at the equivalence point is 8.73 –
phenolphthalein gives color change between the ph range of 8.2 to 10.0.
 For a weak acid and a weak base color indicators are not suitable for use to indicate
the end-point (equivalence point). Color indicators are useful if small quantities of
either titrant is needed to produce sharp recognizable color change. However, for
weak acid/base titration, large quantities of titrants are needed if color change is to
from - this results in huge errors.

A complexometric indicator is an ionochromic dye that undergoes a
definite color change in presence of specific metal ions.[1] It forms a weak
complex with the ions present in the solution, which has a significantly
different color from the form existing outside the complex.
NATURE:
Complexometric indicators are water-soluble organic molecules.
EXAMPLES:
Calcein with EDTA for calcium
Fast Sulphon Black with EDTA for copper
Hematoxylin for copper
Xylenol orange for gallium, indium and scandium
USES:
1.In analytical chemistry, complexometric indicators are used in
complexometric
titration to indicate the end point when all the metal ions in the solution are
sequestered by a chelating agent e.g. EDTA.
2.Analysis of metal ions.

EXPLANATION:
Indicators used in complexometric titration are
to some extent similar to those used in acid-
base titrations. Their color changes depending
on the concentration of metal ions, just like
color of pH indicators changes depending on
the H+ concentration

“A type of indicator used in reactions that involve precipitation
such as precipitation titration”.
Or
“An indicator used in solutions to detect slight excess of a
reactant or ion in a precipitation reaction’’.
EXAMPLE:
The yellow dye Fluorescein
Dichlorofluorescein
Eosin
Di-iodo diethylfluorescein
Tartarazine
Phenosaframine
Rhodamine 6 G

Explanation:
fluorescein is added to an NaCl solution being titrated with silver nitrate.
Fluorescein is used to detect the completion of the reaction of silver ion
with chloride ion. After a quantity of silver large enough to precipitate all
the chloride has been added, additional silver ion is partially adsorbed on
the surface of the particles of silver chloride. Fluorescein also is adsorbed
and, in combining with the adsorbed silver ion, changes from yellow-green
to red.
Use:
these indicator use in argentometry i.e. for the detection of metallic halide
e.g. Nacl titrated against silver nitrate.
WHY THEY ARE TERMED AS ADSORPTION INDICATOR?
At the end point, indicator is absorbed by the precipitate of Agcl, and during
the process of adsorption, a change in color of indicator take places which
indicate s neutralization point so they are called as adsorption indicator.

 UNIVERSAL INDICATOR:
“A universal indicator is a solution which undergoes several color changes
over a wide range of pH's”
 USES:
It is use to determine the ph of various solution , but not use in titration because of
its wide range of ph.
Litmus
Litmus is a natural dye extracted from lichens. It is the most commonly used natural
indicator.
Litmus turns acidic solutions red and basic solutions blue. Neutral solutions do not
change the color of either red or blue litmus.
Turmeric
Turmeric gives brownish red color in basic medium and yellow in acidic medium.
Lemon juice and vinegar turn turmeric yellow and china rose pink

 CHINA ROSE
A solution of china rose turns green in a basic
solution, and bright pink or magenta in an acidic
solution.
IDENTIFICATION OF BASIC SUBSTANCES
Soap, milk of magnesia and limewater turn red litmus paper blue.
This indicates the basic nature of these solutions.
Soap, milk of magnesia and limewater turn turmeric red and the
china rose green.
IDENTIFICATION OF ACIDIC SUBSTANCES
Red litmus paper when dipped in lemon juice and vinegar remains
red. But they turn blue litmus paper red. This indicates the acidic
nature of these solutions.

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Indicator

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