CHEM 104 1st Edition Lecture 28- Svante Arrhenius (1887) definition of acids/baseso Acid = ionizes in aqueous solution to form H+ (protons) HA(aq) H+(aq) + A-(aq) o Base = ionizes in aqueous solution to form HO- (hydroxide) o *But some acids or bases (for example NH3) don’t fit this definition - Brønsted-Lowry (1923) definition of acids/bases o Acid = proton donoro Base = proton acceptor HA(aq) + H2O(l) H30+(aq) + A-(aq) - Molecular compounds/anions/cations can all be acids or bases- Amines are B-L bases – similar to ammonia, lone pair on N used to “accept” the proton - If a compound doesn’t have oxygen, it isn’t a B-L acid- Polyprotic acid = can donate 2 or more protons o Also applies to baseso Ex. of polyprotic acid: phosphoric acid H3PO4- Amphiprotic species = functions as an acid or a base (i.e. can donate or accept a proton) o Ex. is water- Conjugate acid-base pair = pair of molecules/ions that differ from each other by the presence of one proton o Ex.: H2S (acid) + CO32- (base) HS- (conjugate base) + HCO3- (conjugate acid) - H2O(l) (acid) + H2O(l) (base) HO-(aq) + H3O+(aq) o Ion product constant Kw = [HO-][H3O+] = (1*10-7 M)( 1*10-7 M) = 1*10-14 at 25˚Co When hydroxide concentration equals hydronium concentration, solution is neutral; when hydroxide conc. exceeds hydronium conc., solution is basic; when hydronium conc.exceeds hydroxide conc., solution is acidic - pH = -log[H3O+] These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.pOH = -log[HO-] pH + pOH = 14 In pure water at 25˚C: neutral pH = 7, acidic pH < 7, basic pH >
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