Acid-Base Reactions

pH scale, neutralization, and indicator color changes

Acids are substances that release hydrogen ions (H⁺) in water, giving solutions a sour taste and pH below 7. Bases release hydroxide ions (OH⁻), feel slippery, and have pH above 7. The pH scale runs from 0 (extremely acidic) to 14 (extremely basic), with 7 being neutral (pure water). Each step on the pH scale represents a 10-fold change in H⁺ concentration — lemon juice at pH 2 is 100,000 times more acidic than pure water at pH 7. When an acid and base mix, the H⁺ and OH⁻ ions combine to form water (H₂O) in a neutralization reaction. The remaining ions form a salt (like NaCl from HCl + NaOH). Indicators are chemicals that change color at different pH values — universal indicator turns red in strong acid, green at neutral, and purple in strong base. Strong acids (like HCl) fully dissociate in water, while weak acids (like vinegar) only partially release their H⁺ ions.