Question

An alkali is titrated against an acid with given below indicator, which of the following is a correct combination?

• A.

  Base	Acid	End point
  Weak	Strong	colourless to pink

• B.

  Base	Acid	End point
  Strong	Strong	Pinkish red to yellow

• C.

  Base	Acid	End point
  Weak	Strong	Yellow to pinkish red

• D.

  Base	Acid	End point
  Strong	Strong	Pink to colourless

Answer 1

The correct option is C

Base	Acid	End point
Weak	Strong	Yellow to pinkish red

The given indicator is methyl orange. Its pH range is 3.9 − 4.5.
Below 3.9 pH it is pinkish red and above 4.5 it is yellow. Weak base has pH greater than 7, so when methyl orange indicator is added, the solution turns yellow. When this solution is titrated against strong acid, at the end point pH <3.9. So the solution turns pinkish red.
Option (a) and (d) are incorrect because methyl orange colour range is yellow- pinkish red.
Option (b) is incorrect because initially an alkali is taken, so the colour change will be from yellow to pinkish red.
Option (c) is correct