What is the pH of a neutral solution like pure water?

pH scale measures acidity/alkalinity from 0 to 14: pH < 7 = acidic; pH = 7 = neutral; pH > 7 = basic/alkaline. Pure water has pH 7. Logarithmic scale: each integer change is a 10-fold change in H+ concentration. So pH 4 is 10× more acidic than pH 5, 100× more than pH 6. Common substances and approximate pH: stomach acid 1-2; lemon juice 2; vinegar 2-3; orange juice 3-4; coffee 5; rain (natural) 5.6; milk 6.5; pure water 7; blood 7.4; baking soda solution 9; ammonia 11; bleach 12; lye (sodium hydroxide) 14. Acids: substances that donate H+ ions (Brønsted-Lowry definition) or accept electron pairs (Lewis definition). Strong acids fully dissociate (HCl, H₂SO₄); weak acids partially dissociate. Bases: substances that accept H+ ions or donate hydroxide (OH-). Strong bases fully dissociate (NaOH, KOH); weak bases partially. Acid-base reactions produce salt and water. Buffers resist pH change — blood pH maintained 7.35-7.45 by bicarbonate buffer system. pH affects enzyme function; small changes can disrupt metabolism.