Question

Calculations. Preparation of 0.1M phosphate buffer pH=74 1. Calculate the amount mL this buffer. O of NaH2PO4 (MW=120g/mol) you will need to prepare m 100 added to prepare 100ml of phosphate buffer 2. Calculate how many ml of 1M NaOH must be at pH=7.4. MOOS. O Imo.ea gnizim vd som slud 1096 MOOS.O ses to Horse Snodulo bios MOOS.Os lo Im 0.0a bris not to muit

pka=6.86

Answer 1

(11 100 me 0.1 m phosphate buffer contains 0:1 x 100 mol 1000 = 0.01 mol phosphate solution should be 7.4 Here pH of the & pka = 6.86 Now from Henderson - Hasselbalch equation we know, pH = pka + log o [salt] [acid] 7.4 = 6.86 + HPO 4 ) [H₂PO4 [HP042-] - [H₂PO4 ] 3.467 " [H₂PO4 ] - [ HPO4 2-] 31467 0.01 - [H₂PO4 ] 3.467 = 0.002 - 0.288 [H₂PO4 ] 1.288 [H₂PO4 ] = 0.002 : [H₂PO4 ] = 0.0016 mol or So, the 100 mL amount of NaH₂PO4 need to prepare of this buffer solution = 0.0016 mol =(0.0016 x 120 ) 9 = 0.192 g

As NaOH is strong base , rso NaoH must be added in mole will be same as the conc. of HPO ise, (0.01 -0.0016) mol = 0.0084 mol Now, 1 mol Nooth present in 1000 ml soln 0.0084 mol Nooth present in 8.4 ml soln.