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Understanding Temperature and pH in Chemistry

Explore the impact of temperature on pH levels and the ionization of water in this comprehensive lesson. Learn how temperature variations affect the equilibrium constant Kw and the balance between H+ and OH- ions.

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Understanding Temperature and pH in Chemistry

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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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