Question

ACDS AND BASES Calculating the composition of a buffer of a given pH A chemistry graduate student is given 450 ml. of a 0.50 M chloroacetic acid (HCH,CICO,) solution. Chloroacetic acid is a weak acid with What mass of NCH,CICO, should the student dissolve in the HCH.CICO, solution to turn it into a buffer with pH 2.76? 1.310 You may assume that the volume of the solution doesn't change when the NaCH.CICO, is dissolved in it. Be sure your answer has a unit symbol, and round it to 2 significant digits Check

Answer 1

weak acid = CICH2COOH salt = CICH2COONa [ CICH2COONa ] = ? [ CICH2COOH ] = 0.500 M pH = 2.760 M pKa = -log[Ka] = -log[1.3x10-3 ] = 2.89 Calculating concentration: According to Henderson-Hasselbalch equation pH = pka + + log [ salt [ weak acid ] [ CICH2COONa ] [ 0.500 ] 2.76 = 2.89 log – + [ CICH2COONa ] = 0.374 M Volume = 450.0 mL = 0.450 L molar mass of CICH2COONa = 116.48 g/mol concentration = (mass)/(molar mass x volune in L) mass = (concentration x molar mass < Volume in L) mass = 0.374 x 116.48 x 0.450 = 19.605 mass of CICH2COONa = 19.61 g g