Question

An alkali is titrated against an acid with methyl orange as indicator. Which of the following is a correct combination ?
A. ${:(,"Base","Acid","End point",),((a),"Weak","Strong","Colourless to pink",):}$
B. ${:(,"Base","Acid","End point",),((b) , "Strong","Strong","Pinkish red to yellow",):}$
C. ${:(,"Base","Acid","End point",),((b) , "Weak ","Strong","Yellow to pinkish red",):}$
D. ${:(,"Base","Acid","End point",),((b) , "Strong","Strong","Pink to colourless",):}$

Answer 1

Correct Answer - C
pH range of methyl orange is 3.1 - 4.5 . Below 3.1, it is pinkish red and above 4.5, it is yellow.
Weak base has $pH gt 7$. When methyl orange is added to weak base solution, the solution becomes yellow. When the solution is titrated with a strong acid, after the end point, solution is acidic and pH is $lt $ 3.1 . Therefore solution becomes pinkish red.