Principles of Chemistry II © Vanden BoutTodayMore Fun with Acids and BasesThings everyone should know something aboutQuizPrinciples of Chemistry II © Vanden BoutFirst some language for the quizAmphiprotic AcidsThese are the species that are partially protonatedin a polyprotic acidH3PO4 H2PO4- between Ka1 and Ka2HPO42- between Ka2 and Ka3Principles of Chemistry II © Vanden BoutLanguage for weak acidsIonizationH2PO4-(aq) H+(aq) + HPO42-(aq)for amphiprotic, the species is an acidHydrolysis (reaction with water)H2PO4-(aq) + H2O(l) OH-(aq) + H3PO4(aq)for amphiprotic, the species is a basePrinciples of Chemistry II © Vanden BoutBreathing DemoPrinciples of Chemistry II © Vanden BoutWhat is happening in the solution?! A.! ! CO2 is dissolving and hydrolyzing making H2CO3! B.! ! O2 is dissolving making excess OH-! C.! ! N2 is dissolving making the HNO3!! D.! ! the indicator dye is reacting with the N2The solution in getting acidic from the CO2 in peoples breathPrinciples of Chemistry II © Vanden BoutReactions for this equilibriumCO2(g) CO2(aq)CO2(aq) + H2O(l) H2CO3(aq)H2CO3(aq) H+(aq) + HCO3-(aq)HCO3-(aq) H+(aq) + CO32-(aq)pKa1 = 6.37pKa2 = 10.25When the pH is around 7 only Ka1 is relevantPrinciples of Chemistry II © Vanden BoutWho cares?Rising CO2 levels are making the oceans more and more acidic (they are still all slightly basic)Previously lots of CO32- species (the other end of the equilibrium)Adding CO2 slowly shifts equilibrium to the acid endPrinciples of Chemistry II © Vanden BoutMore fun with carbonatesPrinciples of Chemistry II © Vanden BoutWhat is happening?! A.! ! makes H2CO3 which is exothermic and causes the water to boil! B.! ! makes H2CO3 which forms CO2! C.! ! makes CO32- which is exothermic and causes the water to boil!! D.! ! makes H2CO3 which forms in soluble Na2(CO2)3Increasing the H+ concentration protonates the HCO3- makingH2CO3 which decomposes into H2O and CO2Adding an acid to the HCO3-Principles of Chemistry II © Vanden BoutWhy does it work with a weak acid?! A.! ! the pKa of acetic acid is greater than the pKa1 for H2CO3! B.! ! the pKa of acetic acid is smaller than the pKa1 for H2CO3! C.! ! the pKa of acetic acid is equal than the pKa1 for H2CO3!H2CO3 is very weak base pKa1 = 6.37Acetic Acid is a stronger weak acid pKa = 4.75Principles of Chemistry II © Vanden BoutKw = KaKb = 10-14 (25°C)[H+] = (KaCHA)0.5[H+] = (Ka1Ka2)0.5[H+] = CA[H+] = KA(Ca/Cb)[OH-] = (KbCB)0.5[OH-] = (Kb1Kb2)0.5[OH-] = CB[OH-] = KB(Cb/Ca)pKa = logKapH = log[H+]pOH = log[OH-]pH + pOH = 14
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