1. The degree to which a weak base dissociates is givenby the base-ionization constant, Kb. For thegeneric weak base, B B(aq)+H2O(l)⇌BH+(aq)+OH−(aq) this constant isgiven by Kb=[BH+][OH−][B] Strong bases will have a higherKb value. Similarly, strong bases will have a higherpercent ionization value. Percent ionization=[OH−]equilibrium[B] initial×100% Strong bases, for which Kb isvery large, ionize completely (100%). For weak bases, the percentionization changes with concentration. The more dilute thesolution, the greater the percent ionization. Ammonia, NH3, is aweak base with a Kb value of 1.8×10−5.

partA What is the pH of a 0.245 M ammonia solution?

partB What is the percent ionization of ammonia at thisconcentration?

2. To understand the relation between the strength of anacid or a base and its pKa and pKb values. Thedegree to which a weak acid dissociates in solution is given by itsacid-ionization constant, Ka. For the genericweak acid, HA, HA(aq)⇌A−(aq)+H+(aq) and the acid-ionizationconstant is given by Ka=[A−][H+][HA] Similarly, the degreeto which a weak base reacts with H2O in solution is given by itsbase-ionization constant, Kb. For the genericweak base, B, B(aq)+H2O(l)⇌BH+(aq)+OH−(aq) and the base-ionizationconstant is given by Kb=[BH+][OH−][B]

Another way to express acid strength is by usingpKa: pKa=−logKa Another way to expressbase strength is by using pKb:pKb=−logKb

partA: A new potential heart medicine, code-named X-281, isbeing tested by a pharmaceutical company, Pharma-pill. As aresearch technician at Pharma-pill, you are told that X-281 is amonoprotic weak acid, but because of security concerns, the actualchemical formula must remain top secret. The company is interestedin the drug's Ka value because only the dissociated formof the chemical is active in preventing cholesterol buildup inarteries. To find the pKa of X-281, you prepare a 0.086M test solution of X-281 at 25.0 ∘C. The pH of thesolution is determined to be 2.40. What is the pKa ofX-281? pKa=?

3. Classify each salt as acidic, basic, orneutral. (KBr, NaNO2, AlCl3)

4. Rank the following compounds in order of decreasingacid strength using periodic trends. strongest acid to weakest acid(MgH2, HI, HBr, H2Se)