a solution is made by combining 10.0 ml of 17.5 M acetic acid with 5.54 g of sodium acetate and diluting to a total volume of 1.50 L.
a)calculate the pH of the solution.
b) how many grams and milliliters of 14.6 M potassium hydroxide needs to be added so pH=pKa?
c)what is the pH of the solution when 100ml of a 2.25 M HCL is added to the original buffer solution?
Tell me what you don't understand about this. The Henderson-Hasselbalch equation will do all of these. An ICE chart will help with b and c.
To answer these questions, we need to consider the reaction between acetic acid (CH3COOH) and sodium acetate (CH3COONa):
CH3COOH + CH3COONa <-> CH3COO- + CH3COOH2+
Given information:
Volume of acetic acid = 10.0 mL = 0.01 L
Concentration of acetic acid = 17.5 M
Mass of sodium acetate = 5.54 g
Final volume of the solution = 1.50 L
a) To calculate the pH of the solution, we need to find the concentrations of the acid and its conjugate base after the reaction:
1. Calculate the concentration of acetic acid:
Concentration (M) = moles/volume (L)
Moles of acetic acid = concentration × volume
Moles = 17.5 M × 0.01 L = 0.175 moles
2. Calculate the concentration of sodium acetate:
To find the moles of sodium acetate, we need to convert the mass to moles using the molar mass of sodium acetate.
Molar mass of sodium acetate (CH3COONa) = 82.03 g/mol
Moles of sodium acetate = mass (g) / molar mass (g/mol) = 5.54 g / 82.03 g/mol = 0.0675 moles
3. Find the concentrations:
Concentration (M) = moles/volume (L)
Concentration of acetic acid = 0.175 moles / 1.50 L = 0.117 M
Concentration of sodium acetate = 0.0675 moles / 1.50 L = 0.045 M
4. Use the Henderson-Hasselbalch equation to calculate pH:
pH = pKa + log10([conjugate base]/[acid])
The pKa of acetic acid is approximately 4.74.
pH = 4.74 + log10(0.045/0.117)
pH = 4.74 - 0.28
pH ≈ 4.46
b) To calculate the amount of potassium hydroxide (KOH) needed to adjust the pH to equal the pKa (4.74), we can follow these steps:
1. Calculate the concentration of the acetic acid and its conjugate base at pH = pKa:
Set the concentration of acetic acid ([CH3COOH]) equal to the concentration of sodium acetate ([CH3COO-]).
Let the concentration be x M.
Therefore, 0.117 M acetic acid = 0.045 M sodium acetate = x
2. Calculate the volume of acetic acid (V1) and sodium acetate (V2) solutions required:
For acetic acid: V1 = (0.117 M / 14.6 M) × 1.50 L
For sodium acetate: V2 = (0.045 M / 14.6 M) × 1.50 L
3. Calculate the mass of potassium hydroxide (KOH) required:
Moles of KOH = concentration (M) × volume (L)
Moles of KOH = 14.6 M × (V1 + V2)
4. Calculate the mass of KOH:
Mass of KOH (g) = moles of KOH × molar mass of KOH
c) Now, let's calculate the pH of the solution when 100 mL of a 2.25 M HCl is added to the original buffer solution:
1. Calculate the moles of HCl added:
Moles of HCl = concentration × volume
Moles of HCl = 2.25 M × 0.100 L = 0.225 moles
2. Calculate the new concentrations of acetic acid and sodium acetate after adding HCl:
New concentration of acetic acid = 0.175 moles / (1.50 L + 0.100 L)
New concentration of sodium acetate = 0.0675 moles / (1.50 L + 0.100 L)
3. Use the Henderson-Hasselbalch equation to calculate the new pH:
pH = pKa + log10([conjugate base]/[acid])
pH = 4.74 + log10([new sodium acetate]/[new acetic acid])
Substitute the values and calculate the pH.
Please note that the calculations for part b) and c) require additional specific information, such as the values of V1 and V2 or the total volume of the mixture after adding HCl.