1 / 8

Kw , pH

Kw , pH. Kw: the ion-product constant of water. Q: will pure distilled water conduct electricity it will (slightly). If water conducts electricity, ions must exist Water exists as an equilibrium, which is referred to as the self-ionization of water:.

dirk
Download Presentation

Kw , pH

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Kw, pH

  2. Kw: the ion-product constant of water Q: will pure distilled water conduct electricity it will (slightly). • If water conducts electricity, ions must exist • Water exists as an equilibrium, which is referred to as the self-ionization of water: H2O  H+(aq) or H3O+(aq) + OH–(aq) [H+] [OH–] [H+] [OH–] or Kw = Kc = [H2O] Note: H+ is just shorthand for H3O+

  3. Kw • What is the value of Kw? • It has been measured at 1.0 x 10–14 (25 °C) whenthe solution is [H+] > [OH–] acidic [H+] < [OH–] basic [H+] = [OH–] neutral • Pure water is neutral since [H+] and [OH–]

  4. Answers As temperature increases Kw increases. It must be that: H2O + heat  H+ + OH– (increase temp = shift right =  Kw) PE 1 Kw = [H+] [OH–] 1.0 x 10–14 = [H+] [7.8 x 10–6] [H+] =1.28 x 10–9 Thus, the solution is basic: [H+] < [OH–]

  5. pH • A quick method of denoting [H+] is via pH • pH = – log [H+] • The pH scale, similar to the Richter scale, describes a wide range of values • pH = 7 vs. [H+] = 1 x 10–7

  6. Calculations with pH Ans: 4.2 • what is pH if [H+] = 6.3 x 10–5? Enter 6.3 x 10–5 (‘6.3’, ‘exp’, ‘5’, ‘+/-’) Then hit ‘log’, followed by ‘+/-’ • What is [H+] if pH = 7.4? • To solve this we must rearrange our equation • [H+] = 10–pH mol/L • Enter ’10’, ‘xy’, ‘7.4’, ‘+/-’, ‘=‘ 3.98x10–8 M • pH + pOH = 14 • This is related to Kw = 1.0 x 10–14

  7. Equations and practice [H+] = 10–pH [OH–] = 10–pOH pH = –log [H+] pOH = –log [OH–] pH + pOH = 14

More Related