What volume of 0.2 ~M Acetic acid is to be added to 100 ml of 0.4 M Sodium acetate so that a Buffer solution of pH equal to 4.94 is obtained? ( pK _ a of CH ₃ COOH =4.76)

Step-by-step solution

The Henderson-Hasselbalch equation for an acidic buffer is given by: pH = pK _ a + ( [ Salt ] [ Acid ] ) Given pH = 4.94 , pK _ a = 4.76 , and the volume of salt ( V_ s ) = 100 ml with concentration ( M_ s ) = 0.4 M . Let the volume of acid be V_ a with concentration ( M_ a ) = 0.2 M . Substituting the values into the equation: 4.94 = 4.76 + ( M_ s V_ s / (V_ s + V_ a ) M_ a V_ a / (V_ s + V_ a ) ) 4.94 - 4.76 = ( 0.4 100 0.2 V_ a ) 0.18 = ( 40 0.2 V_ a ) Taking the antilog of both sides ( 10^ 0.18 1.5136 ): 1.5136