Methyl Orange

Methyl orange is a pH indicator frequently used in titrations because of its clear and distinct colour change. Because it changes colour at the pH of a midstrength acid, it is usually used in titrations for acids. Unlike a universal indicator, methyl orange does not have a full spectrum of colour change, but has a sharper end point. Methyl orange shows red colour in acidic medium and yellow colour in basic medium.

In a solution becoming less acidic, methyl orange moves from red to orange and finally to yellow with the reverse occurring for a solution increasing in acidity.The entire color change occurs in acidic conditions.In an acid, it is reddish and in alkali, it is yellow. Methyl orange has a pKa of 3.47 in water at 25 °C (77 °F).

Modified (or screened) methyl orange, an indicator consisting of a solution of methyl orange and xylene cyanol, changes from grey-violet to green as the solution becomes more basic.

Since acidic solutions have low pH values, it will be red and transition to orange and yellow as the acidity of the solution decreases. In basic solutions, it will be yellow as well as in neutral solutions because the pH of a neutral solution is approximately 7 and falls after the color change of methyl orange.

Dissolve 0.5 g of bromothymol blue in 500 mL of water. Add a drop of ammonia solution to turn the solution deep blue in colour. Prepare methyl orange acid-base indicator, pH < 3.1 red to pH > 4.4 yellow-orange. It is best for solutions with concentration > M/5.

pH-related color changes result from changes in the way electrons are confined in a molecule when hydrogen ions are attached or detached. Here is the structure of methyl orange in acidic solution: The molecule absorbs blue-green light, which makes its solution appear red.

Methyl orange is a pH indicator frequently used in titrations because of its clear and distinct colour change. Because it changes colour at the pH of a midstrength acid, it is usually used in titrations for acids.