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DOUBLE INDICATOR

TITRATION

Choosing an Indicator in Acid-Base Titrations
Titration curves are used to deternne which indicator(s) is/are suitable fora particular titration

Titration of NezCOs with HCI
enopointI mauesol purpa {,9*9
...
2-4
...
of trant

te

a

pil

tne

rd

ndie
...
0)

***

endpolnt 2methy oranga (3
...


p


...
2-2
...
4-1
...
0-5
...
6

-8
...
8-


...


ATId olo
orang
yclogreen

Base color

O n y r o l hiue 3nd p h n o l red

Sreenea indicato

8

6 b7
...
0

yelow

orngered

ACId C

green

green

dimethryf yellaw and methyfene blua

blue-green

bluevlolot

and metyl orane

*d-violet

romocreot green

violet-:
hlue

promoaeiol greon and chloropiionot red

metryi red and mett»ylene blue

ixed Indicator

? arin yeliovw

cor
moi blye

Dheroi red

ltma

Actd

Choosingan indicatorin Acid-Base

f

su, t

range

at the end-point

colors at the

Indicators are chOsen
...
if the reaction involves
strong base and a weak acid

strong acid and a weak base

Neutral if the reaction involves
a strong acid and a
strong base
Acidic
...


step 2 ind the equivalence point
I t is the steepest part of the curve

The equivalence point can be used to
determine the equivalent weight (molar

mass) of the acid

unsutable: azerin yekow (tco early)

Thration of NaOH with HC

good indicators: bromothymol bue,

Bomus and pheno red

unsutadle: orange IV (too late)

vol
...
methyl orange indicator (ptH-4)

Vino

volume required to reach the imo endpolnt

vofume requlred to reach phe endpoint

vpn *

Vph =Vmo
Vuoztr
Vph

where
Vmo

Co2+H
+

H

+

HOos
H20
Vph< Vmo
Ne2Co3 2Vph
NaHCO3Vmo-Vph

NaHcOg

mo endpoint

phe endpoint

has been converted to

HCO

Na,CO

cO

NaHCO with a Strong Acid

wRh he NaHCO, Is #he some as Uhat
a c t n g with the Na,C0,

(B NacO

ghenaiphiaieh thange1

AO h e i (oe

Is reached when

Step 1 phenolphthalein indicator (pH-9)

[used
certain indicators change color at different stages of a
tiwo end points in
the proportions of the components of certain mixtures byy observing
A
...
50em
Volume of HCI added I cmJ

NaCO

C
...
Titration of a Mixture containing Na,CO3 and Naol with a Strong Acid

oH)
A

-

2Vmo

Vpn

Vph> Vmo

taOH

Nn2C03

Is neutralized and

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