pH

Definition

pH in plain English

PH is just a quick score for how acidic or basic a liquid is, running from about 0 (battery acid) to 14 (drain cleaner), with 7 (pure water) right in the middle. Acids are things loaded with loose hydrogen ions (written as H^+, or H_3O^+ once they grab onto water), and pH is a compact way to report how crowded those ions are. The catch is the scale is 'backwards' and jumps by 10s: a lower pH means MORE acid, and each step of 1 means 10 times more, so pH 3 is ten times as acidic as pH 4. Formally, pH = -log_10[H_3O^+] — the negative log just turns tiny, awkward numbers like 0.001 into a clean '3'.

Practice pH

What is the atom’s net charge?

Related MCAT terms

• Absolute threshold
• Acid
• Acid-base titration curve
• Action potential
• Activation energy
• Active vs passive transport
• Aldol condensation
• Allele
• Amino acid (essential 9)
• Amphipathic