Video narration
Why do lemon juice and soapy water behave so differently? An indicator shows the difference: lemon juice, an acid, changes color one way; soapy water, a base, changes color another. That difference has a measurable place on the pH scale. pH shows whether a liquid is acidic, neutral, or basic: acids are below 7, pure water is neutral at 7, and bases are above 7. That's why: lemon juice is acidic, soapy water is basic, and pH places each one.