1 / 13

pH Scale

pH Scale. Ionization of Water. Water is amphoteric 2H 2 O ↔ H 3 O + + OH – Acid + base K w = [H 3 O + ][OH – ] = 1.0 × 10 –14 at 25°C Acid: [H 3 O + ] > [OH – ] Base: [H 3 O + ] < [OH – ] Neutral: [H 3 O + ] = [OH – ]. Water is Amphoteric. Amphoteric = both acid and base behavior

minerva-nicholson
Download Presentation

pH Scale

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. pH Scale

  2. Ionization of Water • Water is amphoteric • 2H2O ↔ H3O+ + OH– • Acid + base • Kw = [H3O+][OH–] = 1.0 × 10–14 at 25°C • Acid: [H3O+] > [OH–] • Base: [H3O+] < [OH–] • Neutral: [H3O+] = [OH–]

  3. Water is Amphoteric • Amphoteric = both acid and base behavior • Compound can accept or donate H+

  4. Autoprotolysis Water undergoes self-ionisation  autoprotolysis, since H2O acts as an acid and a base. H2O + H2O H3O+ + OH- The extent of autoprotolysis is very small.

  5. [H3O+] [OH-] [H2O]2 Autoprotolysis The equilibrium constant expression for this reaction is: KC = The concentration of water is essentially constant. Therefore: [H2O]2 KC = [H3O+]  [OH-] constant=KW

  6. Ionization of Water • As usual the K value changes with temperature. • In pure water, what are the [H3O+] and [OH–]?

  7. (1.8 x 10-9)2 x 55.5 a2 x C Kd= = = 1 1-a Self Ionization of Water a25°C = 1.8 x 10-9 1.7982 x 10-16

  8. Self Ionization of Water Kd x 55.5 =Kw = [H+][OH-] =9.98 x 10-15 1 x 10-14 Kw = [H+][OH-] = 10-14 [H+] = [OH-] =10-7 mol dm-3

  9. Review of pH • pH = -log [H+] • pX = -log [anything X] • As [H+] goes down, pH goes up, and the opposite also occurs • Higher pH equals lower hydrogen or hydronium ion concentrations…

  10. pH Scale • Neutral: [H3O+] = [OH–] = 1.0 × 10-7 M • Acid: [H3O+] > [OH–] • Base: [H3O+] < [OH–] • Define pH = –log[H3O+] • Reverse calculation [H3O+] = 10–pH • For pure water, pH = –log[1.0 × 10-7] = 7.00

  11. Neutral, Acidic & Basic Conditions • Both ions are present in all aqueous solutions. • You’d think they would neutralize each other. • The do, but equilibrium keeps regenerating the ions. • Inversely proportional • As one goes up, the other goes down

  12. Temperature Changes Things

  13. Beer NaHCO3 Lemon Juice PureWater 0.1 M NaOH pH 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 0.1 M HCl Milk 0.1 M NH3 Pickles Blood Acidity/Basicity of Solutions

More Related