1 / 20

Hydrogen Ions and Acidity

Hydrogen Ions and Acidity. The Ionization of Water and pH. Hydrogen Ions in Water. We are used to thinking of water as a pure liquid that contains only H 2 O molecules. However, as a pure liquid, water ionizes into hydrogen ions and hydroxide ions: H 2 O( l ) → H + ( aq ) + OH - ( aq )

oral
Download Presentation

Hydrogen Ions and Acidity

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. Hydrogen Ions and Acidity • The Ionization of Water and pH

  2. Hydrogen Ions in Water • We are used to thinking of water as a pure liquid that contains only H2O molecules. • However, as a pure liquid, water ionizes into hydrogen ions and hydroxide ions: • H2O(l) → H+(aq) + OH-(aq) • H2O(l) + H2O(l) → H3O+(aq) + OH-(aq)

  3. Hydrogen Ions in Water • The symbol for the concentration of hydrogen ions is [H+] and for hydroxide ions is [OH-]. • We can measure the concentration of the ions in purewater. • [H+] = 1.0×10-7 M • [OH-] = 1.0×10-7 M • By stoichiometry, H2O(l) → H+(aq) + OH-(aq), we see that [H+] = [OH-] in pure water.

  4. Hydrogen Ions in Water • We also know that the product of the concentrations is a constant, Kw. • Kw = [H+][OH-] = 1.0×10-14 • This means that as we change [H+], we change [OH-]. • If [H+] goes up, [OH-] goes down. • If [H+] goes down, [OH-] goes up.

  5. Hydrogen Ions in Water • The higher the value of [H+] and lower the value of [OH-], the more acidic the solution. • The lower the value of [H+] and higher the value of [OH-], the more basic the solution. • For example: [H+] = 1.0×10-6 is acidic. • For example: [H+] = 1.0×10-3 is moreacidic. • For example: [H+] = 1.0×10-8 is basic. • For example: [H+] = 1.0×10-11 is morebasic.

  6. Hydrogen Ions in Water Example 1: Colas are slightly acidic. If a cola solution has [H+] = 1.0×10-5 M, what is the [OH-]? [H+] = 1.0×10-5 M Kw = [H+][OH-] = 1.0×10-14 Kw 1.0×10-14 Kw = [H+][OH-]  [OH-] = = 1.0×10-5 [H+] [OH-] = 1.0×10-9

  7. The pH Concept • pH is another way to measure [H+] and/or [OH-]. • pH = -log[H+] • pOH = -log[OH-] • If [H+] = 1.0×10-7 • then pH = -log(1.0×10-7) = 7.00 • If [OH-] = 1.0×10-7 • then pOH = -log(1.0×10-7) = 7.00

  8. The pH Concept To find pH on the TI-83 or TI-84 Plus ... • press the “(-)” button • press the “LOG” button • enter the value for [H+] • press the “)” button • press “ENTER”

  9. The pH Concept To find pH on the TI-Nspire ... • press the “(-)” button • press the “ctrl” button • press the “10x” button • enter the value for [H+] • press the “)” button • press “ENTER”

  10. The pH Concept • If [H+] = 1.0×10-5 • then pH = -log(1.0×10-5) = 5.00 • If [OH-] = 1.0×10-8 • then pOH = -log(1.0×10-8) = 8.00 • If [H+] = 3.1×10-2 • then pH = -log(3.1×10-2) = 1.51 • If [OH-] = 4.5×10-11 • then pOH = -log(4.5×10-11) = 10.35

  11. The pH Concept • We can also convert from pH and pOH to [H+] and [OH-] respectively. • [H+] = 10-pH • [OH-] = 10-pOH • If pH = 7.00 • then [H+] = 10-7.00 = 1.0×10-7 • If pOH = 3.25 • then [OH-] = 10-3.25 = 5.6×10-4

  12. The pH Concept To find [H+] on the TI-83 or TI-84 Plus ... • press the “2ND” button • press the “LOG” button • press the “(-)” button • enter the pH value • press the “)” button • press “ENTER”

  13. The pH Concept To find [H+] on the TI-Npire ... • press the “10x” button • press the “(-)” button • enter the pH value • press the “)” button • press “ENTER”

  14. The pH Concept • If pH = 2.556 • then [H+] = 10-2.556 = 2.78×10-3 • If pOH = 9.27 • then [OH-] = 10-9.27 = 5.4×10-10 • If pH = 12.12 • then [H+] = 10-12.12 = 7.6×10-13 • If pOH = 6.678 • then [OH-] = 10-6.678 = 2.10×10-7

  15. The pH Concept • pH + pOH = 14 • if pH = 2.0, • then pOH = 14.0 - 2.0 = 12.0 • if pH = 3.250, • then pOH = 14.000 - 3.250 = 10.750

  16. The pH Concept • Solutions with pH = 7 (pOH = 7) are neutral. • Litmus paper remains colorless. • Solutions with pH < 7 (pOH > 7) are acidic. • Litmus paper turns red. • Solutions with pH > 7 (pOH < 7) are basic. • Litmus paper turns blue.

  17. Measuring pH • Indicators may be added to a solution to tell us the range of pH of the solution.

  18. Measuring pH • Indicators are most often used where pH may change, such as in a titration. • But they are also used to tell us where we are in a particular range of pH. • For example, if we wanted to tell if a solution has a pH greater than or less than 7 ... • we might use Bromthymol Blue (which changes color at about pH = 7).

  19. Measuring pH • Indicators are most often used where pH may change, such as in a titration. • But they are also used to tell us where we are in a particular range of pH. • For example, if we wanted to tell if a solution has a pH greater than or less than 7 ... • we would not want to use Methyl Red (which changes color near pH = 5).

  20. Measuring pH • Some meters provide quick and accurate readings of pH. • They vary from the simple to the very complex.

More Related