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Indicators

Part of the Acids and Bases section of Coddy's Chemistry journey. Lesson 24 of 30.

An indicator changes color with the pH. Litmus: red in acid, blue in base.

Red and blue litmus in an acid and a base

Litmus

Phenolphthalein: colorless below about 8, pink above. Methyl orange: red below about 3, yellow above 4.5. Universal indicator: a rainbow from pH 1 (red) to 14 (violet).

Challenge

Universal indicator turns blue in a sample of soapy water, which has [H₃O⁺] = $1.0 \times 10^{-9}\ \mathrm{M}$ . What is its pH, and is it acidic, neutral or basic?

Try it yourself

Acids and basesWork out the solution

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Acids and Bases

1Acids and Bases

What Is an Acid What Is a Base Proton Transfer Conjugate Pairs Water as Acid and Base Recap - Proton Swap

4Neutralization

Neutralization Net Ionic Equations Salts Titration Titration Calculations Recap - Titration Lab

2Strong and Weak

Strong Acids Weak Acids Ions in Acid Solutions Recap - Acid Strength

5Acids Around Us

IndicatorsAcid Rain Antacids Recap - Soil and Lime

3The pH Scale

Ions of Water The pH Scale pH of Strong Acids pH of Strong Bases pOH Diluting an Acid Recap - pH Meter

6Practice Problems

Recap - Vinegar Test Recap - Stomach Acid Recap - Drain Cleaner