pH Scale and Indicators
Ever wondered why lemon juice tastes sour whilst soap feels slippery? It's all about the pH scale, which measures how acidic or alkaline something is on a scale from 0 to 14.
Acids pH0−6 contain lots of H+ ions and turn universal indicator red, yellow, or orange. Think vinegar, citrus fruits, and your stomach acid. Neutral substances like pure water sit right in the middle at pH 7 - they're neither acidic nor alkaline.
Alkalis pH8−14 are packed with OH- ions and turn universal indicator green, blue, or purple. Common examples include soap, bleach, and antacid tablets. The further you move from pH 7, the stronger the acid or alkali becomes.
Different indicators help us identify acids and alkalis through colour changes. Universal indicator gives you the full rainbow of colours, whilst litmus paper simply turns red in acid and blue in alkali. Phenolphthalein stays colourless in acid but turns bright pink in alkali - perfect for spotting the exact moment when neutralisation happens!
Quick Tip: Remember "Red = Acid" for litmus paper, and acids always have pH values below 7.