Question

Part 1B: Acid/Base Indicator Equilibrium Chemical Reaction involved Initial color of the solution: 1. Adding HCI: a. Color change b. Equilibrium shifting 2. Adding NaOH: a. Color change b. Equilibrium shifting

First distilled water was added to a test tube. Then methyl orange indicator was added. The HCl and NaOH.

Answer 1

In alkaline medium, methyl orange indicator gives yellow color. Assume that $In^-$ represents the yellow form of the indicator.

Ov=O Na Yellow form of methyl orange present in alkaline medium In

In acidic medium, methyl orange indicator gives red color. Assume that represents the red form of the indicator.

toto red form of methyl orange present in acidic medium HIN

The equilibrium reacion is

Hin= H+ + In

The initial color is red. This is the color obtained when methyl orage is added to pure water.

1.

HCl is added

a.

Color remains red. No color change is observed.

b.

Equilibrium shifts to left, towards

This is because HCl gives protons. These protons acts as common ions and suppress the ionization of .

2.

NaOH is added

a.

Color changes from red to yellow.

b.

Equilibrium shifts to left, towards $In^-$

This is because NaOH gives hydroxide ions. These hydroxide ions combines with protons to form water. In this way protons are removed from the solution. These protons acts as common ions and their removal increases the ionization of