jaguar7
Nov17-10, 06:32 PM
Haha --- nvm, found it. Sorry/Thanks... ^_^
Where does the 2.19 come from?
How many moles of NaOH would need to be added to 500.0 mL of 0.70 M HClO to create a buffer with a pH of 7.80?
Initially, we have 0.35 mol of HClO. We are going to add NaOH which will react with the weak acid to create the conjugate weak base.
HClO + OH- → H2O + ClO-
It is this weak base we’ll need to have for the buffer. First, let’s find the ratio of the weak base to the weak acid using the Henderson-Hasselbalch equation:
7.80 = -log(3.5*10^(-8) + log(base/acid)
base/acid = 2.19
Since we will be making base from the weak acid, we will react x moles of OH-. So after the reaction takes place, we have 0.35 – x moles of acid and x moles of base.
x / (0.35 - x) = 2.19
x = 0.240 moles
Where does the 2.19 come from?
How many moles of NaOH would need to be added to 500.0 mL of 0.70 M HClO to create a buffer with a pH of 7.80?
Initially, we have 0.35 mol of HClO. We are going to add NaOH which will react with the weak acid to create the conjugate weak base.
HClO + OH- → H2O + ClO-
It is this weak base we’ll need to have for the buffer. First, let’s find the ratio of the weak base to the weak acid using the Henderson-Hasselbalch equation:
7.80 = -log(3.5*10^(-8) + log(base/acid)
base/acid = 2.19
Since we will be making base from the weak acid, we will react x moles of OH-. So after the reaction takes place, we have 0.35 – x moles of acid and x moles of base.
x / (0.35 - x) = 2.19
x = 0.240 moles