Question

1. What is the pH of a buffer solution prepared with a 0.4 M sodium citrate and 1% citric acid (pka for citric acid - 3.13, MW - 192 g/mol)? 8. A buffer solution is prepared using 0.4 mole of a weakly basic drug (pka - 10.1) and an unknown quantity of its salt. The final solution has a pH of 8.99. How much of the salt was used? 9. A buffer solution with a desired pH of 8.15 needs to be prepared with boric acid and sodium borate. Calculate the molar ratio of salt to acid needed to prepare the solution (Ka of boric acid is 5.80 x 10-19).

Answer 1

(7) 1% citric acid = 19 citric acid in 100 ml solution. . 1000 mL solution contains nog citric acid un Molarity = 10g 192 g/mol (MW) 20.052 M [salt .. Using Henderson equation pH = pka + log kereta pka = 3.13 [salt] = 0.4M [acid] =0.052 m -.PH - 3.13 + log 0:has = 313 + 6.886 - pHz 4.016 ~ 4:02 0 0.052

(8) The equilibrium BH + H2O + B + H30t [base Using Henderson equation pHepka + log – [acid] Here [base] = [B] = 0.4 mole/v Thets suppose the volume of [acid] - [salt] - [.BH+] buffen is v. me] = no supose ne number of moles of pka = 10.1 pH = 8.99 salt 0.078 pH = 8.99 = 10.1 + log & (0.4 more() (n/V) $8.99 - 10.1 = log onky => -1.11 = log on the story = 0.078 O n= 0.4 . 5.13 5.13 mole of salt was used. (9) Given Ka of boric acid = 5.808 10 10 i. pka : - log ka = – log (5.80 x 15 10) = 9.24 Here salt = sodium borate and acid boric acid .. pHapka + 104 [salt] [acid] > 8.15 = 9.24 + log [sodium borate] [boric acid] + log [sodium borate] [bonic acid = -1.09 :.. [sodium bonate] [bomic acid7 -0.081