Question

11. How would you prepare 1.00 L buffer with a pH = 4.00 using 1.00 M HF and solid Naf. 12. How would you prepare 1.00 L buffer with a pH = 4.70 using 1.00 M HC2H302 and 0.500 M Na C2H302. 13. How would you prepare 1.00 L buffer with a pH = 4.70 using 1.00 M HC2H30, and solid NaC2H3O2.

Answer 1

11 pH = pka + log [salt] [Aud? Ka of HF = 6.6x104 pka = -log ka = -log(6.6x17") = 3.16 4.00 = 3.1 + log Cart Ilang beset = 0.82 - Celta 6 kmalu [NaF] = 6.6069345 [HEZ number of moles of Nat. volume = 6.607 number of moley of HF volume volume = 1 L buffer solution & number of moles of NaF/L - 6.607 1.00 mol

number of mole of NaF = 6.607 mol molar mass of NQF = 41.988 17 g/mol mass of Naf required = 6-607 mot x 41.98817% = 277.4131 g Answer: by dissolving 277.4131 g of NaF in 1L, 1.00m HF

12) 4.70 = 4.75 +log (Na C₂ H3 02] + [H CH3 02] [NaC₂ H₂ 027 - total millimale total volume Let v ml of NaC, Az is used Nagttiez - 0.500 mol x ml IL (HC2 H20] 1.00 mel x (1000-vmu) IL le 0.5 XV mmol = (1000 - V) mmol -0.05 O.SV - = 0.89125 1000-V

0.5.V=891-25-0.89125 7 1.3912509 = 891.25 = v= 640.61 ml (of NaCa Hz Oz) 1000-1=359.39 ml (of HC₂ H₂O2). Answer: 640 ml of 0.50 m Na H₂O + 360 ml of 1.oom HC H₂02

12 13 4.70 = 4.75 + Log IH Cathol you r boo (Na C₂ H₂ 0₂] (Na C₂ H₂ Og [H GO₂ H₃ T = 0.891251 number of moles of Nachz/1L - Cave = 0.89125) 1.00 ml H (₂} H3/IL . mol of Na C₂ H₂O = 0.891251 mol = 0.891251 mol X 82-034 g/mol = 73.11g Answer: By dissolving 73.119 of Natzo, in C 1.00L of 1.00m HC H₂02