Titration of 50.0 mL of acetic acid reaches equivalence after delivery of 22.5mL of standardized NaOH 0.21 M.
What is the initial concentration of acetic acid and what is the pH of the solution?
What is the pH at equivalence?
What is the pH adition of 20.0 mL of NaOH?
What volume of titrant (NaOH) must be delivered to reach a pH of 4.74?
HAc + NaOH ==> NaAc + H2O
First, determine the molarity of the HAc.
mL x M = mL x M
22.5 x 0.21 = 50*x
x = 0.0945M
Now divide the titration curve into four sections.
a. at the beginning.
b. between initial and eq point
c. eq pt
d. after eq pt
Which of these do you have trouble doing? I see no point in repeating those steps you know how to do.
I figured it out. Thank you!
To calculate the initial concentration of acetic acid and the pH of the solution, we can use the concept of stoichiometry and the properties of the acetic acid in water.
1. Initial concentration of acetic acid:
The balanced chemical equation for the reaction between acetic acid (CH3COOH) and sodium hydroxide (NaOH) is:
CH3COOH + NaOH → CH3COONa + H2O
From the equation, we can determine the stoichiometric ratio between acetic acid and sodium hydroxide:
1 mole of acetic acid reacts with 1 mole of sodium hydroxide.
Given the volume and concentration of the NaOH solution, we can determine the number of moles of NaOH used in the titration:
Volume of NaOH = 22.5 mL = 0.0225 L
Concentration of NaOH = 0.21 M
Number of moles of NaOH = Volume × Concentration = 0.0225 L × 0.21 mol/L = 0.004725 mol
Since the stoichiometric ratio is 1:1, the number of moles of acetic acid present in the initial solution is also 0.004725 mol.
Now, we can calculate the initial concentration of acetic acid:
Volume of acetic acid = 50.0 mL = 0.0500 L
Initial concentration of acetic acid = Number of moles / Volume = 0.004725 mol / 0.0500 L = 0.0945 M
Therefore, the initial concentration of acetic acid is 0.0945 M.
2. pH of the solution:
To calculate the pH of the acetic acid solution, we need to consider the dissociation of acetic acid in water. Acetic acid is a weak acid and partially dissociates into its ions in water:
CH3COOH ⇌ H+ + CH3COO-
The dissociation constant (Ka) of acetic acid is 1.8 × 10^-5. To calculate the pH, we can make use of the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
Where:
pH = the pH of the solution
pKa = -log(Ka)
[A-] = concentration of the acetate ion
[HA] = concentration of the undissociated acetic acid
Given that the molar concentration of acetic acid is 0.0945 M, and the dissociation constant (pKa) is -log(1.8 × 10^-5), we can calculate the pH using the Henderson-Hasselbalch equation.
3. pH at equivalence:
At equivalence, the number of moles of acetic acid and sodium hydroxide are equal. On the basis of the stoichiometry of the balanced equation, the pH of the solution is generally very close to 7. This is because acetic acid is a weak acid and sodium hydroxide is a strong base.
4. pH after the addition of 20.0 mL of NaOH:
To calculate the pH after adding 20.0 mL of NaOH, we need to consider the stoichiometry and the volume of base added. Given that the initial volume of acetic acid is 50.0 mL and the volume of NaOH added is 20.0 mL, we can calculate the new volume of the solution.
Initial volume of acetic acid = 50.0 mL = 0.0500 L
Volume of NaOH added = 20.0 mL = 0.0200 L
New volume of the solution = Initial volume + Volume of NaOH added = 0.0500 L + 0.0200 L = 0.0700 L
Using the Henderson-Hasselbalch equation with the new solution volume and the molar concentration of acetic acid, we can calculate the new pH.
5. Volume of titrant to reach a pH of 4.74:
To calculate the volume of titrant (NaOH) required to reach a pH of 4.74, we can use the Henderson-Hasselbalch equation, rearranged to solve for the concentration of acetic acid:
[HA] = 10^(pH - pKa) × [A-]
Given that the desired pH is 4.74 and the pKa of acetic acid is -log(1.8 × 10^-5), we can substitute these values into the equation to find the concentration of acetic acid. Then, using the volume of acetic acid and the concentration, we can calculate the number of moles of acetic acid. Finally, by applying the stoichiometric ratio, we can calculate the volume of NaOH needed.