A buffer solution is prepared by dissolving 0.400 mol of CH3COOH and 0.200 mol of CH3COONa in 1.00 L of water. 1.00 mL of 10.0 M HCl is added to a 100 mL portion of this solution. What is the final pH of the resulting solution?
Ka of CH3COOH = 1.8 x 10¯5
You want to make an ICE chart and use the Henderson-Hasselbalch equation.
Let's simply our typing by calling CH3COOH just HAc and CH3COONa will be NaAc.
mmoles HAc = 0.400 M x 100 mL = 40.0
mmoles Ac^- = 0.200M x 100 mL = 20.0
mmoles HCl added = 1.00 mL x 10.0 M = 10.0
...............Ac^- + HCl ==> HAc + Cl^-
initial.......20.0.....0......40.0
added................10.0..........
change.......-10.0...-10.0.....+10.0
equil.........10.0....0.........+50.0
Now plug all of that into the HH equation and solve for pH. Post your work if you get stuck.
To find the final pH of the resulting solution, we need to consider the acid-base equilibrium between CH3COOH and CH3COO- in the buffer solution, as well as the additional HCl that was added. Here's how you can solve the problem:
Step 1: Calculate the initial concentration of CH3COOH and CH3COO- in the buffer solution.
Given that 0.400 mol of CH3COOH and 0.200 mol of CH3COONa are dissolved in 1.00 L of water, the initial concentration of CH3COOH and CH3COO- can be calculated as follows:
CH3COOH: 0.400 mol / 1.00 L = 0.400 M
CH3COO-: 0.200 mol / 1.00 L = 0.200 M
Step 2: Calculate the concentration of H+ ions resulting from the addition of HCl.
1.00 mL of 10.0 M HCl is added to a 100 mL portion of the solution. To find the concentration of H+ ions resulting from this addition, we need to consider the dilution factor.
The initial volume of the solution before adding HCl is 100 mL, or 0.100 L.
Using the formula for dilution, we can calculate the new concentration of H+ ions as follows:
(10.0 M) x (0.001 L) / (0.100 L + 0.001 L) = 0.099 M
Step 3: Set up the equilibrium expression for the reaction between CH3COOH and H2O.
CH3COOH + H2O ⇌ CH3COO- + H3O+
The equilibrium constant expression for this reaction, using the given Ka value, is:
Ka = [CH3COO-][H3O+] / [CH3COOH]
Step 4: Use the Henderson-Hasselbalch equation to calculate the pH of the resulting solution.
The Henderson-Hasselbalch equation for a buffer is given by:
pH = pKa + log([A-] / [HA])
Where pH is the desired final pH, pKa is the negative logarithm of the acid dissociation constant (Ka), [A-] is the concentration of the conjugate base (CH3COO-), and [HA] is the concentration of the weak acid (CH3COOH).
In this case, we know the pKa value (given as Ka), the concentrations of CH3COO- and CH3COOH (from Step 1), and the concentration of H+ ions resulting from the addition of HCl (from Step 2).
Plugging in the values, the equation becomes:
pH = -log(1.8 x 10^-5) + log(0.200 M) / 0.400 M) + log(0.099 M)
By calculating this equation, you will get the final pH of the resulting solution.