Question

What is the pH of a solution that consists of 0.50 M H2C6H6O6 (ascorbic acid) and 0.75 M NaHC6H6O6 (sodium ascorbate)? What is the pH if 20.0 mL of a 0.280 M perchloric acid is added to 200.mL of the ascorbic acid sodium ascorbate solution? What is the pH if 30.0 mL of a 0.125 M sodium hydroxide is added to 200.mL of the ascorbic acid sodium ascorbate solution? The ionization constant for ascorbic acid is 6.8 x 10–5

Answer 1

pH of ascorbic acid and sodium ascorbate solution = 4.35

pH after addition of perchloric acid = 4.306

pH after addition of sodium hydroxide = 4.373

0.5 m ascorbic acid and 0.75 M Sodium ascorbate 108ms a bubbex Solution ka = 6.8*105 pka = -log ka = -log (6.8x10-5) [pka = 4.17] 0 pH = pka + log (NaHCGHG 06) (H₂ C6H606] PH = 4.17 +10g (075) O.S pH = 4.17+ 0.1761 (pH = 4.35] © added to 20 ml 06 0.280 M perchloric acid 200 ml of bulbes--solution Milli moles of perchloric acid - 20 X 0:28 x = 5.6 mmol Before addition of perchloric aud millimoles o ascorbic acid = 0.5x200 = 100 mmol millimoleso sodium ascorbate = 0.75 x 200 = 150 mmol

Abtex addition of a perchloric acid millimoles of ascorbic acid : 100 + x = 100+5.6 = 105.6 mmol millimoles of sodium ascorbate = 150-x. = 150-5.6 - 144.4 mmol total volume = 200 + 20 = 220 ml PH = pka + log CNaHC6H6O6] [H₂ C6H6O6] pH = 4.17 + log (144.4/220) (105.6 /220) pH = 4.17 + log (1944) 105.6 PH = 4.17 +0.136 1pH = 4.306 3 30 ml 06 0.125 M of buffer solution NaOH added to 200 m Millimoles 06 NaOH = 30X0.125 - 3.75 mmol

After addition 06 Nach millimoles 06 ascorbic acid : 100 -3.75 = 96.25 mmol millimoles of sodium ascorbate = 150+ 3.75 = 153.75 mmol total volume = 230 ml pH = pka + log [NaHC6H6O6] [H2C6H606] PH = 4.17 + log (153.75/230) (96.25/230) pH = 4.17 + log ( 53,75) pH = 4.17 + 0.203 1pH = 4.373