CHEM 108 1st Edition Lecture 21Chapter 16 Acid–Base and Solubility Equilibrium continuedFactors affecting strengths of Acids and Bases:- Molecular structure can be used to rationalize strengths of a series of acids or bases - Effect of size and bond strength: HF <HCl<HBr< HI o increase size, decrease HX bond strength, increase strength of acid- Effect of electronegativity: CH4 < NH3 < H2O < HF o increase electronegativity of atom adjacent to H, increase polarity of bond, increase strength of acido The more electronegative the main atom the more it pulls electron density away from the hydrogen atoms and the more easily the hydrogen atom ionizes and the stronger the acid.- Oxoacid: H-O-Y o As electronegativity of Y increases, acid strength increases: HOI <HOBr<HOCl- The greater the number of oxygens, the stronger the acid.o The more oxygen atoms there are in an acid, the higher the oxidation number of the main atom and therefore the more electronegative it will be when it dissociates.Acid-Base Properties of Salts:- Weak Acid: HF(aq) (acid) + H2O(l) ⇌ F− (aq) (conj. base) + H3O+ (aq) - The Salt, NaF: NaF(s)dissociated in water Na+ (aq) + F− (aq) - F− (aq)(base) + H2O(l) ⇌ HF(aq) (conj. acid) + OH− (aq) - Thus when NaF dissolves in water it creates a slightly basic solution because F− (aq) is a strong base. pH of salt solutions:- F− (aq) + H2O(l) ⇌ HF(aq) + OH− (aq)- Determine Ka or Kbo Kb= ([HF][OH−])/[F−] using I.C.E tableso pOH=-log[OH−]o pH= pKw- pOH ( pKw= 14)- By Solving equilibrium problem for [H+], [OH−] you can determine pH of the solution.Aqueous solutions of salts can be acidic, basic, or neutral - To predict, dissociate salt and determine if cations and anions are acids, bases, or neutral o conjugate bases of strong acids are neutral o conjugate acids of strong bases are neutral o conjugate bases of weak acids are weak bases o conjugate acids of weak bases are weak acids- Ex: NaClo Na+ is the conjugate acid of NaOH, NaOH is a strong baseo so Na+ is neutral Clis the conjugate base of HClo HCl is a strong acid, so Cl is neutral o NaCl is neutral- Ex: NH4F o NH4+ is conjugate acid of NH3o NH3 is a weak base, so NH3 + is a weak acid o Fis conjugate base of HF o HF is a weak acid, so Fis a weak base o Ka for NH4+ is 5.56 10-10o Kb for Fis 1.59 10-11o Ka> Kb , so solution is acidicRelationship between Ka and Kb:- Kw=Ka*Kbo Kw= 1*10-14o Ka = equilibrium constants for acido Kb = equilibrium constants for
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