Consider the titration of 20.0mL of 0.300M acetic acid, HAc, with 0.150M NaOH solution. Ka=1.75*10^-5
HAc + NaOH ---> NaAc + H2O
What is the composition of the solution at the equivalence point of the titration? Give both the formula of the compound and its concentration.
Calculate the pH at the equivalence point of the titration.
20*0.300 = x mL*0.150
Solve for x mL = 40 mL
Total volume at equivalence point is 40 + 20 = 60 mL
HAc + NaOH ==> NaAc + H2O
So the solution at the equivalence point is sodium acetate, NaAc, and the concn is millimols/mL = (20*300)/60 mL = ? = approx 0.1 The pH at the equivalence point is determined by the hydrolysis of the acetate ion.
..........Ac^- + HOH => HAc + OH^-
I.........0.1...........0......0
C........-x.............x......x
E......0.1-x............x......x
Kb for Ac^- = (Kw/Ka for HAc) = (x)(x)/(0.1-x)
Solve for x = (OH^-) and convert to pH.
Thank you so much. You cleared things up.
To determine the composition of the solution at the equivalence point, we need to find the moles of acetic acid, HAc, and sodium hydroxide, NaOH, that react.
Step 1: Find the moles of HAc.
Given that the volume of 0.300 M HAc is 20.0 mL (or 0.0200 L), we can use the formula:
moles = concentration × volume
moles of HAc = 0.300 M × 0.0200 L
Step 2: Find the moles of NaOH.
Since the balanced equation shows 1:1 stoichiometry between HAc and NaOH, the moles of NaOH are the same as the moles of HAc.
moles of NaOH = moles of HAc
Step 3: Calculate the concentration of the resulting compound.
The balanced equation shows that HAc and NaOH react to form sodium acetate, NaAc, and water. At the equivalence point, all the acetic acid has reacted, resulting in a solution containing sodium acetate and water. The concentration of NaAc can be found by dividing the moles of NaOH by the total volume of the solution after the reaction is complete.
total volume of solution = volume of HAc + volume of NaOH
total volume of solution = 20.0 mL + 20.0 mL
total volume of solution = 40.0 mL (or 0.0400 L)
concentration of NaAc = moles of NaOH / total volume of solution
Now, let's calculate it:
moles of NaOH = 0.300 M × 0.0200 L
concentration of NaAc = (0.300 M × 0.0200 L) / 0.0400 L
The resulting compound is sodium acetate, NaAc, with a concentration of [NaAc] = (0.300 M × 0.0200 L) / 0.0400 L.
Moving on to calculating the pH at the equivalence point:
At the equivalence point, the moles of NaOH and HAc are equal. The reaction between NaOH and HAc forms a salt, sodium acetate (NaAc), which is the conjugate base of the weak acid acetic acid (HAc).
NaAc can hydrolyze in water to produce hydroxide ions (OH-). The resulting solution is basic, and the pH can be calculated using the hydrolysis reaction:
NaAc + H2O ⇌ NaOH + HAc
Since NaOH is a strong base, it dissociates fully to produce hydroxide ions (OH-). The concentration of OH- can be found by multiplying the concentration of NaOH by the stoichiometric ratio:
[OH-] = [NaOH]
Finally, use the equation for the hydrolysis of the acetate ion (Ac-) to calculate the concentration of hydroxide ions in the solution:
Kw = [OH-] [HAc] / [NaAc]
The Ka (dissociation constant) of acetic acid can be used to find the concentration of HAc:
Ka = [H+][Ac-] / [HAc]
Since the concentration of HAc is the same as that of NaAc at the equivalence point, we can set up the equation:
Ka = [H+][Ac-] / [NaAc]
Solving for [H+], we get:
[H+] = (Ka × [NaAc]) / [Ac-]
Finally, calculate the pH using the equation:
pH = -log10 [H+]
By following these steps, you will be able to determine the composition of the solution and calculate the pH at the equivalence point of the titration.