In: Chemistry
Perform the appropriate calculation to determine the theoretical pH of the buffer solution after 10 drops of 0.1M HCl was added. Ka of acetic acid = 1.8 x 10-5
Suppose, moles of the acid in the buffer be 0.23 mol and the conjugate base be 0.17 mol. (Because nothing has been mentioned about the buffer solution in the question)
Volume of 10 drops of HCl = (0.5 x 10 ) mL = 5 mL = 0.005 L
Moles of HCl added = (0.1 x 0.005 ) mol = 0.0005 mol
HA -----> H+ + A-
Initial 0.23 mol - 0.17 mol
Change + 0.0005 mol - ( - 0.0005 ) mol
Equilibrium 0.2305 mol - 0.1695 mol
pH = pKa + log (A- / HA)
pKa = -log ( 1.8 x 10 ^-5) = 4.74
pH = 4.74 + log ( 0.1695/ 0.2305) = 4.74 - 0.133 = 4.607