Question

CHEM 104 Homework 6 4. (15 points): Chapter 18.6 Quinine (C20H24N:02), a compound extracted from the bark of tropical cinchona trees, was the first effective treatment for malaria and is still used today. The quinine molecule, shown at right, contains two basic nitrogen atoms, N. (pKo = 5.1) and Nz (pKo = 9.7). a) Compare the pk, values of N, and N, and calculate the corresponding Ke values. Which nitrogen is more basic? CH H O b) Medicinal quinine is given as the salt of its conjugate acid, quinine hydrochloride (C20H12N2O-HCI), which is much more soluble in water. Use the Ko of the more-basic nitrogen you determined from part a to calculate the K, of quinine hydrochloride. c) What is the pH of an antimalarial formulation containing 1.5% by mass of quinine hydrochloride in water? Use 1.00 g/mL for the density of H2O.

Answer 1

• Molecular mals of Quinine C C 20 Hz u Nabr) 12х10 +1х24 + 14х2 +10x2 - 324 4 > given pkb N4 = 5.1, pkb N2 = 9.7 Nr 11 к., 5 , I", (к), 41 90 5.) (кЬ) - 16 1 , (к) : « , (к), - Го". , alo » (th) - 16. 10° - (kb/n = 7.94 x10 , (Kb) Ny = 2x10-10 -> allo in any ionization reaction of a bars :- BOH ² Btton (BOH is a base) aolt-d) and and I . К. : Св1 Cou] - Гвои] (а (5) = 7-44 хо, (к) = 2х(а 10 см 19 мазit и O we kntu +4+ Кь Гон) . Мt K, Maw Mov [и 1, 60 м, і, моYt bои с.

(6) we know that during the hydrolysis of a base. Ik haka= kw/ Kb .. KalCro Hau N2O2. HC () = KW kb (N) - Kai 10-14 ... = 1.25 x 10 9 7.94x10-6 - Moler mais (1) given of of quinine hyd so chloride in H2O - 1.5% by mass 1.5 gram quinine in 98.5 gram H₂O ! Moles of quinine wyd so chloride = ls. ~ Moler mass of quinine hydrochlunde = mass of quinine + mass of Hel= 324 + 36,5 = 360.5 M a Molesa lis 360.5 = 0.0041 Moleg

2. Molarity 0.004) ( deurity of H₂O=1 qgis : vol of 98.5 gram. 1000 l water 2985 me a 4.1 0,042 moler allo (ht] = J. Kaxao = 1 1.25x10 9 x 0.042 98.5 & Crt] = {oisas x105 = 0.72x10-s - PH₂ -log(t) = 5 - log(0.72) = 5.14