1 / 25

Acidity and pH

Acidity and pH. Review. Acids are substances that: taste sour. react w/ bases to form salts and water. are electrolytes. turn blue litmus red. produce H 3 O +1 ions in aqueous solution. donate H +1 ions (protons). Review. Bases are substances that: taste bitter.

ipo
Download Presentation

Acidity and 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. Acidity and pH

  2. Review • Acids are substances that: • taste sour. • react w/ bases to form salts and water. • are electrolytes. • turn blue litmus red. • produce H3O+1 ions in aqueous solution. • donate H+1 ions (protons).

  3. Review • Bases are substances that: • taste bitter. • react w/ acids to form salts and water. • are electrolytes. • turn red litmus blue. • produce OH-1 ions in aqueous solutions. • accept H+1 ions (protons).

  4. Autoionization • H2O + H2O  H3O+1 + OH-1 • Extremely small Keq. • Keq = Kw = 1.0 x 10-14 • Only 0.00001% of H2O molecules autoionize. • In pure water, [H3O+1] = 1.0 x 10-7 Molar. • [OH-1] also equals 1.0 x 10-7 M. • Less than 2 H3O+1 and OH-1 ions per billion water molecules. • Since [H3O+1] = [OH-1], water is pH neutral. • Adding an acid or a base upsets this balance.

  5. Autoionization H O H O H H - +

  6. Adding an Acid to Water HA HA HA HA HA H2O H2O H2O A-1 H3O+1 H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H3O+1 H2O H2O H3O+1 A-1 H2O A-1 H3O+1 H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O A-1 H2O H3O+1 H2O H2O H2O A-1 OH-1 H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O

  7. Adding a Base to Water A-1 A-1 A-1 A-1 A-1 H2O H2O H2O H2O HA OH-1 H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O OH-1 H2O OH-1 H2O HA H2O HA OH-1 H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O OH-1 HA H2O H2O H2O HA H3O+1 H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O

  8. 1x10-1 M 1x10-1 M 1x10-2 M 1x10-2 M 1x10-3 M 1x10-3 M Neutral Solution 1x10-4 M 1x10-4 M 1x10-5 M 1x10-5 M 1x10-6 M 1x10-6 M Acid added to neutral solution 1x10-7 M 1x10-7 M 1x10-8 M 1x10-8 M Base added to neutral solution 1x10-9 M 1x10-9 M 1x10-10 M 1x10-10 M 1x10-11 M 1x10-11 M 1x10-12 M 1x10-12 M 1x10-13 M 1x10-13 M As [H3O+1] Increases, [OH-1] Decreases [OH-1] [H3O+1]

  9. [H3O+1] and [OH-1] in Water • In any aqueous solution: • [H3O+1] [OH-1] = 1x10-14 • As [H3O+1] goes up, [OH-1] must decrease. • As [OH-1] goes up, [H3O+1] must decrease. • In other words, adding an acid to water causes the solution to become more acidic and less basic. • Adding a base to water causes the solution to become less acidic and more basic.

  10. [H3O+1] and [OH-1] in Water • If [H3O+1] = 1x10-3 M, what is [OH-1]? • [H3O+1][OH-1] = 1x10-14 • (1x10-3 M)[OH-1] = 1x10-14 • [OH-1] = (1x10-14) / (1x10-3) • [OH-1] = 1x10-11 M • If [OH-1] = 1x10-8 M, what is [H3O+1]? • [H3O+1][OH-1] = 1x10-14 • [H3O+1](1x10-8 M) = 1x10-14 • [H3O+1] = (1x10-14) / (1x10-8 M) • [H3O+1] = 1x10-6 M

  11. Acidity • Acidity • How much H3O+1 is dissolved in a sol’n. • Remember, acids increase [H3O+1] in solutions. • Acidity = pH.

  12. pH • pH = power of Hydrogen • negative logarithmic (powers of ten) scale. • pH = -log10[H3O+1] • If [H3O+1] = 1x10-1 M, • pH = -log(1x10-1 M) = 1 • If [H3O+1] = 1x10-2 M, • pH = -log(1x10-2 M) = 2 • If [H3O+1] = 1x10-3 M, • pH = -log(1x10-3 M) = 3

  13. A Few Words About Logarithms • The logarithm of a number is the power to which you would have to raise a base to equal that number. • Unless otherwise indicated, assume the base is 10. • log(100) = 2 • because 102 = 100 • log(1000) = 3 • because 103 = 1000 • log(0.001) = -3 • because 10-3 = 0.001 • log(0.000 001) = -6 • because 10-6 = 0.000 001

  14. Why Use Logarithms At All? • The [H3O+1] and [OH-1] of an aqueous solution can vary by a very large degree. • [H3O+1] = 1 M for a very acidic soln • [H3O+1] = 1x10-7 M for a neutral soln • [H3O+1] = 1x10-14 M for a very basic soln • 1 M is ten million times greater than 1x10-7 M. • If you tried to plot both concentrations on the same graph, 1x10-7 M would barely register above zero. • If 1x10-7 M was 1 mm above the 0 mark, the axis would have to be ten kilometers (six miles) tall to show 1 M. • Logarithms allow us to compare numbers that are widely different by thinking of them as powers of ten.

  15. This graph shows pH as a function of hydrogen ion concentration. It isn’t a very useful graph because it is hard to get accurate information for [H3O+1] below 1x10-3 M.

  16. In this graph the x-axis is logarithmic. It allows a much greater range of data to be displayed in a readable format.

  17. pH • Each unit decrease in pH is a 10-fold increase in acidity. • Imagine a soln with a pH of 5. • A soln with a pH of: • 4 is 10 times more acidic. • 3 is 100 times more acidic. • 2 is 1000 times more acidic. • 1 is 10,000 times more acidic. • 0 is 100,000 times more acidic.

  18. pH Scale

  19. pH Scale

  20. pH Scale

  21. pH Scale

  22. pH Scale

  23. [H3O+1] and [OH-1] [H3O+1] [OH-1]

  24. pH and pOH • What are the pH values of the following solutions? • 1x10-1 M H3O+1 • pH = -log(1x10-1 M) = 1 • 1x10-3 M H3O+1 • pH = -log(1x10-3 M) = 3 • 1x10-5 M H3O+1 • pH = -log(1x10-5 M) = 5 • 1x10-1 M OH-1 • [H3O+1] = (1x10-14) / (1x10-1 M) = 1x10-13 M • pH = -log(1x10-13 M) = 13

  25. [H3O+] and [OH-] • Given pH, you can calculate [H3O+1] and [OH-1]. • [H3O+1] = 10-pH • [H3O+1] [OH-1] = 1x10-14 • If pH = 2, • [H3O+1] = 1x10-2 M • [OH-1] = 1x10-12 M

More Related