Question

An analytical chemist is titrating 66.3 mL of a 0.9100 M solution of benzoic acid (HCH,CO2) with a 0.8600 M solution of NaOH. The pK, of benzoic acid is 4.20. Calculate the pH of the acid solution after the chemist has added 77.8 mL of the NaOH solution to it. Note for advanced students: you may assume the final volume equals the initial volume of the solution plus the volume of NaOH solution added. Round your answer to 2 decimal places. pH= 0 x h

Answer 1

• - Soln As this is a reaction of strong Base & Weak acid. We can write the reaction as GlycooH + NaOH e o usloona 66.3 ml 0.9100m 0.8600 77.8ml + H2O 6.083x10' milsmolo 6.033 milimales 3 6.69 x 10 mils moles . As some Na oH is still left in the solution There fore first we should caleulate the remaing moles of Naon. I 66.9 - 60.33 - 6. 578 milemoles O ) " = 0.04564 6.578 concentration concentration of Na oH = (77.8 +66.3) . : [OH-] = 0.0456 Pon = -log[ou ] =- log [o .0456] 1.341 . . PH = 14- 1.341 - 12.66 Note There is no need for calculating anything with Pka of weak and as there is still strong base left in the solution,