What is an Indicator in Chemistry? Types and Examples

Natural indicators are obtained from natural sources like plants.

• Litmus: Extracted from lichens. It turns red in acidic solutions and blue in basic solutions.
• Turmeric (Haldi): A common household spice. It remains yellow in acids but turns deep red when exposed to a base (like soap).
• Red Cabbage Juice: Turns red in acidic solutions and green/yellow in basic solutions.

Synthetic indicators are chemical compounds manufactured in laboratories specifically for acid-base titrations and testing.

• Phenolphthalein: A colorless liquid. It remains colorless in acidic solutions but turns vibrant pink in basic solutions.
• Methyl Orange: It shows a red/pink color in acidic mediums and turns yellow in basic mediums.

While most indicators change color, olfactory indicators change their smell depending on whether they are mixed with an acid or a base. This is especially useful for visually impaired students.

• Onion Extract: Loses its strong smell in a basic solution, but retains its smell in an acidic one.
• Vanilla Extract: The pleasant smell vanishes in the presence of a base but remains noticeable in an acid.

A universal indicator is a mixture of several different indicators. Instead of just indicating 'acid' or 'base', it displays a range of different colors depending on the exact pH of the solution. It turns red for strong acids, green for neutral solutions (pH 7), and dark purple for strong bases.