What is the pH after 0.023 moles of HCl is added to a 100.0mL buffer solution containing 0.65M HOBr and 0.55M NaOBr ? Ka HOBr = 2.5 x 10-9
Ka = 2.5 *10-9
pKa = -log ( 2.5 *10-9) = 8.60
Moles of HOBr = Molarity * Volume = 0.65 M *100 mL = 0.65 mol/L *0.100L = 0.065 moles
Moles of NaOBr = 0.55mol/L *0.100L = 0.055 moles
Now HCl is added, then it will reacts with NaOBr and forms HOBr
Thus, Moles of NaOBr added = 0.055 moles - 0.023 moles = 0.032 moles
Moles of HOBr = 0.065 moles + 0.023 moles = 0.088 moles
Using henderson Hasselbalch equation
pH = pKa + log[salt]/[acid]
pH = 8.60 + log( 0.032 / 0.088 ) = 8.16
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