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Lesson 19 Temperature and pH

Lesson 19 Temperature and pH. Kw and Temperature. Energy + H 2 O ⇋ H + + OH -. @ 25 o C Kw = 1.0 x 10 -14. Higher Temperatures. @ 50 o C shifts right. Kw > 1.0 x 10 -14. pH < 7. [H + ] > 1.0 x 10 -7 M. pOH < 7. [OH - ] > 1.0 x 10 -7 M.

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Lesson 19 Temperature and pH

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  1. Lesson 19 Temperature and pH

  2. Kw and Temperature Energy + H2O ⇋ H+ + OH- @ 25 oC Kw = 1.0 x 10-14 Higher Temperatures @ 50 oCshifts right Kw > 1.0 x 10-14 pH < 7 [H+] > 1.0 x 10-7 M pOH < 7 [OH-] > 1.0 x 10-7 M @ this temperature pH + pOH = pKw < 14

  3. Kw and Temperature Energy + H2O ⇋ H+ + OH- @ 25 oC Kw = 1.0 x 10-14 Lower Temperatures @ 0 oCshifts left Kw < 1.0 x 10-14 pH > 7 [H+] < 1.0 x 10-7 M pOH > 7 [OH-] < 1.0 x 10-7 M @ this temperature pH + pOH = pKw > 14

  4. Important Points If you're not @ 25oC [H+][OH-] ≠ 1.0 x 10-14 pH + POH ≠ 14 All other equations are valid and……. Pure wateris always neutral, but pH ≠ 7and……. [H+] = [OH-] and …… pH = pOH

  5. 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

  6.  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 M pH = pOH = 6.15 pKw = 12.30

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