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