Question

Although not as common, it is possible to prepare a buffer solution in non- aqueous solvents. Consider a 1.000 L solution of liquid ammonia (auto- ionization constant = 10-33) that has 0.3000 moles of di-isopropyl amine (pka = 36 relative to water) and 0.4000 moles of LDA added to it. a. Write out the autoionization reaction for ammonia. List the acid/base definitions that apply to this reaction and identify the most precise definition b. Approximate the pka of di-isopropyl amine in ammonia. Use a pka = 9.26 for the ammonium ion in this approximation. c. Calculate the ammonia-based pH for this buffer solution.

Answer 1

@ The aukolonization reaction kore ammonia is T 2NH3(1) NHAT + NH₃- The acid/base definitions that apply to this reaction are Acid is defined as a substance that dissociates to give hydrogenious when dissolved in water and a base is a substance which dissociates into hydroxylions. when dissolved in watere (Armchanius concept. 6 Bronsted-Lowry concept: Acid is defined as a substance which has a tendency to donate a proton. to any other substance and a base is a substance which has a rendency to accept a preoton from any other substance. W Lewis concept: An acid is a species that is capable of accepting a paire of electrons to forem a covalent bond and a base is a species that is capable of donating a baire of electrons to forum a covalent bond. Harce, in this recaction, the most preecisa definition is m. 3 M₂ M3 M3 H& CN My ( diisobreobyl amine) (LDA – Lithiumdii sobreobylanide (weak acid) (streong base (6 pka of diisopropyl amine in ammonia - .:P" = pka + log Isacid] weak acid - strong) 13 см, [-Z alt base -> pka _ph_log (sally

=> pka = 9.26-log 13000 .4000 = 9.26 0.12 = 9.14 . O Auto-ionization constant, a = 1033 We know, from weakacid - strong base buffer- pH-spka + 1 pk w + 2 log c -(* *9.14) + (3 x34) + (£109°3). = 4.57 + 1-0:26 = 11.31 lbih Station
diisopropyl amine is a weak acid and LDA is a strong base. Weak acid-strong base buffer calculations are done like this.