16.1 Introducing pH scale

A. General concept All aqueous solutions contain H2O, therefore, they contains H+ and OH- Acidity and alkalinity depends on the difference between [H+] and [OH-] If [H+] larger than [OH-] : Acidic [H+] = [OH-] : Neutral [H+]smaller than [OH-] : Alkaline B. Calculating pH value pH = -log [H+] pH has no unit! [ ] means molar concentration, with the unit M When pH decreases by 1 (more acidic), [H+] increases 10 times ~!!! Because of log ~! **Pay attention to calculating pH of polybasic acid : e.g. 2M H3PO4 : pH = -log [2 x 3 ] due to each molecule produces 3 H+ ion. ~!! C. pH Scale Range from 0 to 14. But we have solution smaller than 0 or larger than 14. Recognize the pH value of some daily commodity. e.g. Alkaline: Window clearner, drain clearner, soap, baking soda Acidic: orange juice, coke, stomach juice, car battery