1 / 11

Water as and Acid and a Base pH Scale

Water as and Acid and a Base pH Scale. Pg 569 - 581. Ionization and Concentration. Amphoteric substance : can act as an acid or as a base Water is the most common amphoteric substance Self-ionization of water: H 2 O(l) + H 2 O(l) H 3 O + ( aq ) + OH - ( aq ).

malachi-sanford
Download Presentation

Water as and Acid and a Base 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. Water as and Acid and a Base pH Scale Pg 569 - 581

  2. Ionization and Concentration • Amphoteric substance: can act as an acid or as a base • Water is the most common amphotericsubstance • Self-ionization of water: H2O(l) + H2O(l) H3O+(aq) + OH-(aq)

  3. Self-ionization of Water • At 25oC actual concentrations are: • [H3O+] = [OH-] = 1.0 x 10-7 M • The product of the two concentrations is: • [H3O+]*[OH-] = 1.0 x 10-14 @ 25oC • We call this Kw • To simplify the equation, we write H3O+ as H+ • Kw = [H+]*[OH-] = 1.0 x 10-14 @ 25oC

  4. Self-ionization of Water • Kw= ion-proton constant • In any aqueous solution at 25oC, no matter what it contains, the product of [H+] and [OH-] must ALWAYS equal 1.0 x 10-14 • What will happen if the concentration of H+ increases? If it decreases? • If [H+] increases, [OH-] decreases • If [H+] decreases, [OH-] increases

  5. Using Kw to Classify Solutions • [H+] = [OH-] neutral • [H+] > [OH-] acidic • [H+] < [OH-] basic Remember: [H+]*[OH-] = 1 x 10-14

  6. Calculate [H+] or [OH-] as required for each of the following solutions at 25 °C, and state whether the solution is neutral, acidic, or basic. • 1.0 x 10-5M OH- H+ = 1.0 x 10-9M, basic • 1.0 x 10-7M OH- H+ = 1.0 x 10-7M, neutral • 10.0 M H+ OH- = 1.0 x 10-15M, acidic • Calculate [H+] in a solution in which [OH-] = 2.0 x 10-2 M. Is this solution acidic, neutral or basic? • 5.0 x 10-13M, basic

  7. pH scale • pH measures the “power” of the hydrogen ion • “Power” refers to exponent of 10 • Based on the base 10 log scale. • pH = -log[H+] • If [H+]= 1.00 x 10-7, pH = ? • If [H+]= 1.00 x 10-2, pH = ? • [H+] = inverse log (-pH) • If pH = 9, [H+]=? • If a solution has a pH of 2, how much more acidic is it than a solution with a pH of 4? • 100 times more acidic!!

  8. pH Examples Try the following: • Find pH if [H+] = 3.5 x 10-3 Find pH if [OH-] = 1.4 x 10-3 2. If the pH = 9.4 what is [H+] ? If the pH = 4.9 what is [OH-] ? Answers: 1) 2.45 2) 11.15 3) 4.0 x 10-10 4) 7.9 x 10-10

  9. Figure 16.3: The pH scale.

  10. Calculating pOH • pOH= -log[OH-] • If pH = 5, What would pOH be? • pH + pOH = 14.00

  11. Sample Problems • The pOH of a solution is 5.67. What is the [OH-] of the solution? What is the [H+]? • The [OH-] of drain cleaner is 3.2 x 10-11M. What is the pOH? The pH? Is it acidic, basic or neutral? • 2.1 x 10-6M and 4.8 x 10-9M • 10.50 and 3.50 = acidic!!

More Related