1 / 32

Acids and Bases

Acids and Bases. GLY 4241 - Lecture Fall, 2014. Acids. Hydronium ion:. Acids are substances that dissociate to donate protons (Brønsted definition) General Formula: H 2n+1 O n +. Lone Pair Acceptor. Lewis definition of an acid is any substance that accepts a lone pair of electrons

jelani-holloway
Télécharger la présentation

Acids and Bases

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. Acids and Bases GLY 4241 - Lecture Fall, 2014

  2. Acids Hydronium ion: Acids are substances that dissociate to donate protons (Brønsteddefinition) General Formula: H2n+1On+

  3. Lone Pair Acceptor • Lewis definition of an acid is any substance that accepts a lone pair of electrons • Important when studying catalysis

  4. “Acidic” Rocks • Term means any rock containing an excess of nonmetallic oxide (principally silica) over metallic oxides • Many nonmetallic oxides (CO2, SO2, SO3, NO2, etc.) will dissolve in water to yield acids (H2CO3, H2SO4, etc.) and this is the reason that nonmetallic oxides were originally called acidic • However, SiO2 is almost insoluble in water and therefore the term, acidic, applied to silica is very misleading.

  5. Attempt to Correct • An effort to replace the term acidic by the word felsic occurred • The older literature still contains references to acidic rocks, however • Many geologists continued to use the term acidic • So the word has now been redefined as weight percent silica content, not referring to the pH of any solution in contact with the rock

  6. Bases • Bases yield hydroxide ion to solution (classical) • Brønsted modified this definition to be that of a proton acceptor

  7. Basic and Ultrabasic Rocks • The terms basic and ultrabasic rocks also exist in the older literature • These terms describe rocks with an excess or a large excess of metallic oxides (MgO, CaO, FeO, etc.) over nonmetallic oxides • Today these terms are replaced by the words mafic and ultramafic • The terms basic and ultrabasic may be used with the silica weight percent classification of igneous rocks, however • Alkaline was and is used for rocks with an excess of Na2O or K2O over SiO2

  8. Dissociation of Water

  9. Dissociation Constant of Water • pH is the negative log of the hydrogen ion concentration • For water:

  10. Strong Acid • Strong acids dissociate completely in water • Thus a 0.1M solution of nitric acid will have [H+] = 0.1 = 10-1

  11. Strong Base • A strong base will dissociate completely to yield OH- ions • Thus a 0.01M solution of NaOH will have [OH-] = 0.01 =10-2

  12. p(OH) • If [OH-] = 10-2,

  13. Ionization Constant • Many substances do not dissociate completely in water including weak acids, weak bases, and salts • For these substances an ionization constant similar to that for water is needed • An example is hydrofluoric acid. • KHF = 10-3.2

  14. Weak Acids and Bases

  15. Multifunctional Acid Groups • First ionization constant

  16. Multifunctional Acid Groups 2 • Second ionization constant

  17. Multifunctional Acid Groups 3 • Third ionization constant • Five species (H+, PO43-, HPO42-, H2PO4-, H3PO4) will be present at equilibrium

  18. Charge Balance • There are more unknowns than equations, so we need additional equations • These can be charge balance equations:

  19. Total Phosphate Concentration • Or, if the substance is totally dissolved and the total concentration of phosphate is known • If the substance did not dissolve totally then a solubility product equation could be set up

  20. Multifunctional Base Groups • First ionization constant • Similar expressions hold for the second and third constants

  21. Approximations • K2 is weaker than K1 by a factor of 10-4- 10-6 • Thus the total concentration of H+ or OH- is, for practical purposes, given by K1 alone

  22. Use of Approximation • For a 0.01M solution of H3PO4:

  23. Approximation Failure • If K1 is large (≥ 10-2) this approximation begins to fail because [H+] is not small in comparison to [HnA] • On the other hand, if the concentration is too low then the [H+] calculated will be less than that for pure water, and this approach fails again

  24. Ionization of Salt • Multiple ionization constants in salts

  25. Salts Which Produce Neutral Solutions

  26. Strong Base & Weak Acid • The salt of a strong acid and a weak base or a strong base and a weak acid often produce an acidic or a basic solution, respectively. • Li+ will not interact with either H+ or OH- ions • Li+ ions do not affect the pH of the solution

  27. Strong Base & Weak Acid 2 • CO32- can and does interact with H+

  28. Weak Base and Strong Acid • This reduces the [OH-] and makes the solution acidic

  29. Heavy Metal Salts • Soluble salts of heavy metal ions will produce acidic solutions

  30. Hydrolysis Constant

  31. Application of Hydrolysis Constant

  32. Calculation of Hydrolysis Constant

More Related