Here is a concise explanation of the concepts of acid, base, and indicator: Acid:

• An acid is a substance that increases the concentration of hydrogen ions (H⁺) or hydronium ions (H₃O⁺) in an aqueous solution.
• Acids typically have a pH less than 7 and can donate protons (H⁺ ions) to other substances.
• Examples include hydrochloric acid (HCl) and acetic acid (CH₃COOH).

Base:

• A base is a substance that increases the concentration of hydroxide ions (OH⁻) or can accept protons (H⁺ ions) in an aqueous solution.
• Bases typically have a pH greater than 7.
• Examples include sodium hydroxide (NaOH) and ammonia (NH₃).

Indicator:

• An acid-base indicator is a compound, usually a weak acid or weak base, that changes color depending on the pH of the solution.
• Indicators undergo a chemical equilibrium where their protonated and deprotonated forms have different colors.
• They are used to visually determine the acidity or basicity of a solution, often during titrations.
• For example, phenolphthalein is colorless in acidic solutions but turns pink in basic solutions above pH 8.3.
• Methyl orange is red in acidic solutions and yellow in basic ones.
• The choice of indicator depends on the expected equivalence point pH in a titration.

These indicators provide a convenient method to estimate the pH of solutions by changing colors at specific pH ranges, making acid-base analysis accessible without electronic pH meters.