Question

What is the colour of methyl orange in acidic and basic medium respectively?

• A. Yellow, Red
• B. Red, Yellow
• C. Colourless, Red
• D. Colourless, Yellow

Answer 1

The correct option is B Red, Yellow

$\left(B\right)$ Red, Yellow

$Reason$ : Methyl orange is a natural pH indicator used in titration or used to test whether a substance/a solution is acidic or basic in nature.It is orange in colour. The indicator changes its colour depending on the pH of the solution.

At pH values less than $3.1$, methyl orange is $red$ and a pH values greater than $4.4$, it will be $yellow$.In the range between $3.1$ and $4.4$, it will be a mixture of red and yellow, such that in the middle of this range, the solution will appear to be orange.

Since acidic solution has low pH values, it will be red and transition to orange or 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 colour change of methyl orange.

$Note$ : Methyl orange has a $p{K}_a$ of $3.47$ in water at ${25}^{o}C$.