What volume of 0.2 M CH ₃ COOH needs to be added to 100 ml of 0.4 M CH ₃ COONa ^2 solution to prepare a buffer of pH equal to 4.91 ? ( pK _ a of CH ₃ COOH is 4.76)

Step-by-step solution

The Henderson-Hasselbalch equation for an acidic buffer is given by: pH = pK _ a + ( [ Salt ] [ Acid ] ) Given pH = 4.91 , pK _ a = 4.76 , and the concentration of salt [ CH ₃ COONa ] = 0.4 M with volume V_ s = 100 ml . Substituting the values into the equation: 4.91 = 4.76 + ( n_ salt n_ acid ) 0.15 = ( 0.4 100 0.2 V_ a ) Taking the antilog of both sides: 10^ 0.15 = 40 0.2 V_ a 1.4125 = 40 0.2 V_ a 0.2 V_ a = 40 1.4125 0.2 V_ a = 28.3186 V_ a = 28.3186 0.2 = 141.59 ml Answer: 141.59 ml