Presentation on theme: "Bases Sodium hydroxide Preferred IUPAC name Systematic name"— Presentation transcript:
1Bases Sodium hydroxide Preferred IUPAC name Systematic name Sodium oxidanideOther namesCaustic soda LyeBasesGraphics Source: Wikipedia
2Acid/Base Definitions Arrhenius ModelAcids produce hydrogen ions in aqueous solutionsBases produce hydroxide ions in aqueous solutionsBronsted-Lowry ModelAcids are proton donorsBases are proton acceptorsLewis Acid ModelAcids are electron pair acceptorsBases are electron pair donors
3Dissociation of Strong Bases MOH(s) M+(aq) + OH-(aq)Strong bases are metallic hydroxidesGroup I hydroxides (NaOH, KOH) are very solubleGroup II hydroxides (Ca, Ba, Mg, Sr) are less solublepH of strong bases is calculated directly from the concentration of the base in solution
4Reaction of Weak Bases with Water The base reacts with water, producing its conjugate acid and hydroxide ion:CH3NH2 + H2O CH3NH3+ + OH- Kb = 4.38 x 10-4
5Kb for Some Common Weak Bases FormulaConjugate AcidKbAmmonia NH3 NH4+ 1.8 x 10-5 Methylamine CH3NH2 CH3NH3+ 4.38 x 10-4 Ethylamine C2H5NH2 C2H5NH3+ 5.6 x 10-4 Diethylamine (C2H5)2NH (C2H5)2NH2+ 1.3 x 10-3 Triethylamine (C2H5)3N (C2H5)3NH+ 4.0 x 10-4 Hydroxylamine HONH2 HONH3+ 1.1 x 10-8 HydrazineH2NNH2 H2NNH3+ 3.0 x 10-6 Aniline C6H5NH2 C6H5NH3+ 3.8 x 10-10 Pyridine C5H5N C5H5NH+ 1.7 x 10-9
6Reaction of Weak Bases with Water The generic reaction for a base reacting with water, producing its conjugate acid and hydroxide ion:B + H2O BH+ + OH-(Yes, all weak bases do this – DO NOTendeavor to make this complicated!)
7A Weak Base Equilibrium Problem What is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?Step #1: Write the equation for the reactionNH3 + H2O NH4+ + OH-
8A Weak Base Equilibrium Problem What is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?Step #2: ICE it!NH3 + H2O NH4+ + OH-ICE0.50- x+x+xxxx
9A Weak Base Equilibrium Problem What is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?Step #3: Set up the law of mass actionNH3 + H2O NH4+ + OH-Exxx
10A Weak Base Equilibrium Problem What is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?Step #4: Solve for x, which is also [OH-]NH3 + H2O NH4+ + OH-Exxx[OH-] = 3.0 x 10-3 M
11A Weak Base Equilibrium Problem What is the pH of a 0.50 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?Step #5: Convert [OH-] to pHNH3 + H2O NH4+ + OH-Exxx
13Text Pg do question 16.75Then you can practice for hw 16.76
14For conjugate acid base pairs only Ka x Kb = KwpKa = -logKapKb = -logKbpKa + pKb = 14Now do question on Pg. 713
15Hydrolysis of Salts Salt of strong acid and strong base – neutral Salt of weak acid and strong base – basicSalt of strong base and weak acid – acidicIn general Ka>Kb acidicKb>Ka basicSoft cover book Pg. 387
17Reactions of Anions with Water Anions are bases.As such, they can react with water in a hydrolysis reaction to form OH− and the conjugate acid:X−(aq) + H2O(l)HX(aq) + OH−(aq)
18Reactions of Cations with Water Cations with acidic protons (like NH4+) will lower the pH of a solution.Most metal cations that are hydrated in solution also lower the pH of the solution.
19Reactions of Cations with Water Attraction between nonbonding electrons on oxygen and the metal causes a shift of the electron density in water.This makes the O-H bond more polar and the water more acidic.Greater charge and smaller size make a cation more acidic.
20Effect of Cations and Anions An anion that is the conjugate base of a strong acid will not affect the pH.An anion that is the conjugate base of a weak acid will increase the pH.A cation that is the conjugate acid of a weak base will decrease the pH.
21Effect of Cations and Anions Cations of the strong Arrhenius bases will not affect the pH.Other metal ions will cause a decrease in pH.When a solution contains both the conjugate base of a weak acid and the conjugate acid of a weak base, the affect on pH depends on the Ka and Kb values.
22Factors Affecting Acid Strength The more polar the H-X bond and/or the weaker the H-X bond, the more acidic the compound.Acidity increases from left to right across a row and from top to bottom down a group.
23Factors Affecting Acid Strength In oxyacids, in which an OH is bonded to another atom, Y, the more electronegative Y is, the more acidic the acid.
24Factors Affecting Acid Strength For a series of oxyacids, acidity increases with the number of oxygens.
25Factors Affecting Acid Strength Resonance in the conjugate bases of carboxylic acids stabilizes the base and makes the conjugate acid more acidic.
26Lewis Acids Lewis acids are defined as electron-pair acceptors. Atoms with an empty valence orbital can be Lewis acids.
27Lewis Bases Lewis bases are defined as electron-pair donors. Anything that could be a Brønsted–Lowry base is a Lewis base.Lewis bases can interact with things other than protons, however.