Question

Calculate the volume of 0.531 mol/L propanoic acid (C2H5COOH, pKa = 4.88) that must be added to 60.0 mL of 0.450 mol/L calcium propanoate (Ca(C2H5COO)2) to prepare a buffer solution with a pH of 5.00.

Calculate the volume of 0.531 mol/L propanoic acid (CH-COOH, PK, -4.88) that must be added to 60.0 mL of 0.450 mol/L calcium propanoate (Ca(CH.COO).) to prepare a buffer solution with a pH of 5.00. 77 mL 98 mL 136 ml 68 ml 220 mL 11 ml 38.5 mL 154 mL

Answer 1

Given that Conc. of Ca(C2H5COO)2 = 0.450 mol/L Number of moles of Ca(C2H5COO)2 = M*V = 0.450 mol/L * 60.0 mL = 27 mmol Number of moles of C2H5000-1 = 2 * moles of Ca(C2H5COO)2 = 2 * 27 mmol = 54 mmol pH of the solution is determined by Henderson equation, pH = pKa+log (CH,C00"] ° [CH,COOH] Bio [C,H,C00-] 5.00 = 4.88+log ICH COOH] [C,H,COO-] -0.12 = log2 [C,H,COOH) [C,H,C00-] -100.12 [C,H,COOH] [C,H,C00-] –1318257 [C,HCOOH] moles of C,H,C00/total volume -=1.318257 moles of C,H,COOH/ total volume moles of C,H,C00 =1.318257 moles of C,H,COOH moles of C,H-COOH = moles of C,H,C00- 1.318257 54 mmol moles of C H2COOH = = 40.96319 mmol 1.318257 Molarity of C,H,COOH = 0.531 mol/L moles Volume of C,HCOOH=" 40.96319 mmol -=77.14348 mL molarity 0.531 mol/L Volume of C,H,COOH to be added = 77 mL Option A is the right answer