2 pH ScaleCreated to express acidity as a more simple number than molarity.pH stands for “power” of the hydrogen ion concentration.pH = - log [H+]If [H+] = 1 x then pH = 7 (neutral)[H+] = 1 x then pH = 3 (acid)[H+] = 1 x then pH = 10 (base)It is based on a logarithmic scale which has a base power of 10.A pH of 1 differs from a pH of 2 by a factor of 10.
3 How to calculate pH….What is the pH of a solution with a [H+] = 4.2 x 10-10M?pH= -log [H+]= -log (4.2 x 10-10)= 9.38Enter into calculator like thisor,Enter 4.2 x in calculator and hit log button, then remove (-) sign.
4 To find the [H+] from pH [H+] = 10-pH Determine the [H+] of a solution with a pH = 6.35.[H+] = 10-pH[H+] =[H+] = 4.47 x 10-7 MFind the “log” button on your calculatorAbove this button it should say “10x”You can use the 2nd key and this button to “un-log” the pH.But, remember to put the (-) sign on the pH first!!
5 pOH We can also express the [OH-] as pOH pOH = -log [OH-] pOH stands for the “power of the hydroxide ion.”pOH<7 is basicpOH=7 is neutralpOH>7 acidic
6 pH and pOH together pH + pOH =14 What is the pH of a solution which has a pOH of 11.2 ? Is this solution acidic or basic?pH = 14pH = 2.8So, the solution is acidic.
7 What is the pH of a solution with a [OH-] = 4.0 x 10–11M? Step 1: Find pOHpOH = -log[OH-]= -log (4.0 x 10-11)= 10.40Step 2: Find pH usingpH + pOH = 14pH = 14pH = 3.60