1 / 23

Acid-Base Theories

Acid-Base Theories. The “Boyz”. Arrhenius Theory of Acids. Acid: molecular substances that breaks-ups in aqueous solution into H+ and anions H + (“hydrogen ions” or “protons”) H + gives acids its protons Example: HNO 3(aq)  H + (aq) + NO 3 – (aq). Common Acids.

ludwig
Download Presentation

Acid-Base Theories

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. Acid-Base Theories The “Boyz”

  2. Arrhenius Theory of Acids • Acid: molecular substances that breaks-ups in aqueous solution into H+ and anions • H+ (“hydrogen ions” or “protons”) • H+ gives acids its protons • Example: HNO3(aq) H+(aq) + NO3–(aq) Acid and Base Theories

  3. Common Acids Acid and Base Theories

  4. Arrhenius Theory of Bases • Base: releases OH– ions in aqueous solution • OH– (hydroxide) • OH– gives bases their properties • Example: NaOH (aq) Na+ (aq) + OH– (aq) Acid and Base Theories

  5. Common Bases Acid and Base Theories

  6. Limitations of Arrhenius Theory • H+ does not exist in solution • More likely to find H+ attached to H2O (hydrated) • H3O+ • Some bases, like ammonia, do not fit this definition, the solution is basic, but the compound does not dissociate, forming hydroxide ion • NH3(g) + H2O (l) NH4+(aq) + OH-(aq) • Limited to the solvent water, but acid-base reactions can occur in other solvents Acid and Base Theories

  7. Bronsted and Lowry • Thomas Lowry • London (England) Johannes Bronsted Copenhagen (Denmark) Acid and Base Theories

  8. Brønsted–LowryTheory of Acids and Bases • Acid: proton (H+) donor HCl + NH3 NH4+ + Cl– • HCl donates a H+ to NH3 • H+ does not exist by itself Acid and Base Theories

  9. Bases: accept a proton H2O + NH3 NH4+ + OH– • NH3 accepts a H+ from H2O • A Brønsted -Lowry acid must have a H in its • formula (like an Arrhenius acid) • Any negative ion can be a Brønsted -Lowry • base Acid and Base Theories

  10. For an acid-base reaction: • There must be a transfer of a proton • A substance can behave as an acid, if another substance behaves as a base • i.e. there is a proton donor (acid) and a proton acceptor (base) HCl (aq) + H2O (l) H3O+(aq) + Cl-(aq) acid base conjugate conjugate acid base Acid and Base Theories

  11. Conjugate acid-base pair • The two molecules or ions related by transfer of a proton from one to the other Example. HCl (aq) and H2O (l) • HCl donates the proton and H2O receives the proton Acid and Base Theories

  12. Conjugate base of an acid • The particle remaining when the proton is removed from the acid • HCl (aq) – acid • Remove proton  Cl-(aq) (conjugate base) Conjugate acid of a base • The particle produced when a base receives a proton • H2O (l) – base • Add proton  H3O+(aq) (conjugate acid) Acid and Base Theories

  13. Conjugate Acid-Base Pair Practce H2SO4 + H2O  HSO4- + H3O+ H2SO4 & HSO4- H3O+ & H2O HCl + NH3  Cl- + NH4+ HCl & Cl- NH4+ & NH3 NH3 + H2O  NH4+ + OH- H2O + OH- NH4+ & NH3 Acid and Base Theories

  14. Table 1: Comparing the Arrhenius and Brønsted-Lowry Theory Acid and Base Theories

  15. The Acid Ionization Constant, Ka • The reaction of a weak acid, HA, with water forms a dynamic equilibrium involving H3O+ and a conjugate base, A- HA(aq) + H2O(l) ⇋ H3O+(aq) + A-(aq) Acid and Base Theories

  16. The equilibrium constant, Ka, is called the acid ionization constant • Ka is used for reactions in which an acid, HA(aq), reacts with water to form a conjugate base, A-(aq) Acid and Base Theories

  17. The equilibrium law for HA(aq) + H2O(l) ⇋ H3O+(aq) + A-(aq) Ka = Acid and Base Theories

  18. Ka = • We know H+(aq) does not exist as individual ions in aqueous solution; rather, every hydrogen ion is bound to water molecule as a hydronium ion, H3O+(aq) • For convenience, we can simply write HA(aq) separating into H+(aq) and A-(aq) Acid and Base Theories

  19. Ka= • Second, when the concentration of a substance remains constant during a reaction, that substance is omitted from the equilibrium law equation • In a dilution solution, we assume the concentration of water remains constant, therefore we can omit H2O(l) Acid and Base Theories

  20. Ka = Simplified… where [H+(aq)] is equivalent to [H3O+(aq)] Acid and Base Theories

  21. A Competition for Protons HA(aq) + H2O(l) ⇋ H3O+(aq) + A-(aq) acid base conjugate conjugate acid base • If H2O has a much greater affinity for H+ than does A- (if it is a stronger base), the equilibrium position will be far to the right • Most dissolved acid will be in the ionized form at equilibrium Acid and Base Theories

  22. A Competition for Protons HA(aq) + H2O(l) ⇋ H3O+(aq) + A-(aq) acid base conjugate conjugate acid base • If A- has a much greater affinity for H+ than does H2O, the equilibrium position will be far to the left • Most dissolved acid will be present at equilibrium as HA(aq) molecules Acid and Base Theories

  23. Learning Checkpoint p. 532 Practice UC # 1, 2, 3

More Related