Molality= molsolute 9.79 kgsolvent0.777-12.6m (c)[4 marks]Calculate the boiling point of a 5 m aqueous solution of ethanol,C2HOH. For water,Ko=0.51 C kg mol" △T。=K,m =0.51Ckgmol-'(5.0molkg') =2.55℃ Thus,T。=100.00°C+2.55°C =102.55C C6.(a)[10 marks]Calculate the pH of an aqueous solution that is 2.5 M triethylamine.(C2Hs)N K for this compound is 5.6x10 (C2Hs)3N+H2O Y(C2H5)3NH)+OHa) (C2Hs)3N (C2Hs)3NH'(a)OH9 Initial 2.5 0 Change -X +X +X Equilibrium 2.5-x 2器2x=5610 25*56×10 x2≈2.5(5.6×104) x2=1.4×10-3 ×=0.0374 Thus,[OH(a】=x=0.0374 pOH=-logIo[OH(ag]=-logIo(0.0374)=1.43molsolute 9.79 Molality 12.6m kgsolvent 0.777 = == (c) [4 marks] Calculate the boiling point of a 5 m aqueous solution of ethanol, C2H5OH. For water, Kb = 0.51 o C kg mol-1 b b o 1 o o o b o T Km 0.51 Ckgmol (5.0molkg ) 2.55 C Thus,T 100.00 C 2.55 C 102.55 C − − Δ = = = = + = 1 C6. (a) [10 marks] Calculate the pH of an aqueous solution that is 2.5 M triethylamine, (C2H5)3N. Kb for this compound is 5.6 x 10-4 (C2H5)3N + H2O(l) Ý (C2H5)3NH+ (aq) + OH- (aq) (C2H5)3N (C2H5)3NH+ (aq) OH- (aq) Initial 2.5 0 0 Change -x +x +x Equilibrium 2.5-x x x 4 2 4 2 4 2 3 x(x) 5.6 10 2.5 x x 5.6 10 2.5 x 2.5(5.6 10 x 1.4 10 x 0.0374 − − − − = × − ≈ × ≈ × = × = ) Thus, [OH- (aq)] = x = 0.0374 pOH = -log10[OH- (aq)] = -log10(0.0374) = 1.43