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  4. An alkali is titrated against an acid with methyl orange as indicator, which of the following is a correct combination? Base Acid End point Strong Strong Pink to colourless Weak Strong Colourless to pink Strong Strong Pinkish red to yellow Weak Strong Yellow to pinkish red

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Q. An alkali is titrated against an acid with methyl orange as indicator, which of the following is a correct combination?
Base Acid End point
Strong Strong Pink to colourless
Weak Strong Colourless to pink
Strong Strong Pinkish red to yellow
Weak Strong Yellow to pinkish red

NTA AbhyasNTA Abhyas 2020Redox Reactions

Solution:

Methyl orange is weak organic base. It is used in the titration of weak base vs strong acid.

$\underset{\underset{\left(\right. \text{Yellow} \left.\right)}{\text{Unionized form }}}{M e O H}\rightleftharpoons Me^{+}+\underset{\underset{\left(\right. \text{Red} \left.\right)}{\text{Ionized form}}}{O H^{-}}$

In basic medium, equilibrium lies in backward direction and therefore it shows yellow colour.

In acidic medium, equilibrium shifts in forward direction and therefore, colour changes from yellow to red.