Lesson 19Temperature
and pH
Kw and Temperature
@ this temperature pH + pOH = pKw < 14
pOH < 7
pH < 7
[OH-] > 1.0 x 10-7 M
[H+] > 1.0 x 10-7 M
Kw > 1.0 x 10-14@ 50 oC shifts right
Higher Temperatures
@ 25 oC Kw = 1.0 x 10-14
Energy+ H2O ⇋ H+ + OH-
Kw and Temperature
@ this temperature pH + pOH = pKw > 14
pOH > 7
pH > 7
[OH-] < 1.0 x 10-7 M
[H+] < 1.0 x 10-7 M
Kw < 1.0 x 10-14@ 0 oC shifts left
Lower Temperatures
@ 25 oC Kw = 1.0 x 10-14
Energy+ H2O ⇋ H+ + OH-
Important Points
If you're not @ 25oC
[H+][OH-] ≠ 1.0 x 10-14
pH + POH ≠ 14
All other equations are valid and…….
Pure water is always neutral, but pH ≠ 7 and…….
[H+] = [OH-] and ……
pH = pOH
1. The pH of pure water is 6.50 Is the temperature higher or lower than 25 oC? Calculate the Kw.Energy + H2O ⇋ H+ + OH-
Higher
[H+] = 10-6.50 = 3.1623 x 10-7 M
[OH-] = 3.1623 x 10-7 M
Kw = [H+][OH-] = (3.1623 x 10-7)2
Kw = 1.0 x 10-13
2. The Kw = 5.0 x 10-13 for pure water. Is the temperature higher or lower than 25 oC?Calculate the pH , POH, and pKw.Energy + H2O ⇋ H+ + OH-
Kw > 1.0 x 10-14
shifted right……temperature is higher
Kw = 5.0 x 10-13 = [H+][OH-] = x2
x = [H+] = 7.071 x 10-7 MpH = pOH = 6.15 pKw = 12.30