Say, for example, that you had prepared a Buffer C, in which you mixed 8.203 g of sodium acetate, NaC2H3O2, with 100.0 mL of 1.0 M acetic acid.
a. What would be the initial pH of Buffer C? HOW???????
•8.203 g*(1mol/82.024g)=0.1mol/.1L=1.0 M NaC2H3O2
•pH= pKa+log[NaC_2 H_3 O_2 ]/[acetic acid]
•pH= -log (1.8x10^-5)+log(1.0 M NaC2H3O2)/(1.0 M acetic acid))= 4.75
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Well, Buffer C sounds like an exciting concoction! Let me explain how we can calculate the initial pH using a bit of chemical clownery!
First, we need to find the moles of sodium acetate, NaC2H3O2, and acetic acid, CH3COOH, in our mixture.
For sodium acetate:
Moles = mass / molar mass
Molar mass of NaC2H3O2 = 82.03 g/mol
Moles of NaC2H3O2 = 8.203 g / 82.03 g/mol
For acetic acid:
Moles = concentration x volume
Concentration of acetic acid = 1.0 M
Volume of acetic acid = 100.0 mL = 0.1 L
Moles of CH3COOH = 1.0 M x 0.1 L
Now, we need to calculate the moles of the acetate ion, C2H3O2-, and the hydronium ion, H3O+.
Since sodium acetate is a salt, it will dissociate completely, giving us one mole of acetate ion for every mole of sodium acetate.
Moles of C2H3O2- = moles of NaC2H3O2
As for acetic acid, it will partially dissociate, so we have to use the Henderson-Hasselbalch equation.
pH = pKa + log([A-] / [HA])
Here, [A-] is the concentration of the acetate ion, and [HA] is the concentration of the undissociated acetic acid.
The pKa for acetic acid is approximately 4.75.
Now, we can calculate the initial pH using this equation with the initial concentrations.
But remember, this is a pH circus trick, and the final answer may contain some clownish comedy!
So, let's crunch the numbers and find out the initial pH of Buffer C!
To determine the initial pH of Buffer C, we would need to calculate the pH based on the concentrations of the acid and conjugate base present in the solution.
The Henderson-Hasselbalch equation can be used to calculate the pH of a buffer solution:
pH = pKa + log ([A-]/[HA])
Where:
pH: the pH of the solution
pKa: the acid dissociation constant of the weak acid in the buffer
[A-]: the concentration of the conjugate base (sodium acetate)
[HA]: the concentration of the weak acid (acetic acid)
First, we need to find the pKa value of acetic acid, which is the acid dissociation constant. For acetic acid, the pKa value is 4.75.
Next, we calculate the concentrations of the conjugate base ([A-]) and weak acid ([HA]):
Concentration of sodium acetate ([A-]):
Using the molar mass of sodium acetate and the mass of sodium acetate, we can calculate the number of moles of sodium acetate:
Molar mass of NaC2H3O2 = (22.99 g/mol) + (12.01 g/mol * 2) + (1.01 g/mol * 3) + (16.00 g/mol * 2) = 82.03 g/mol
Number of moles of NaC2H3O2 = mass / molar mass
Number of moles of NaC2H3O2 = 8.203 g / 82.03 g/mol = 0.100 mol
Concentration = number of moles / volume
Concentration of NaC2H3O2 = 0.100 mol / 0.100 L = 1.0 M
Concentration of acetic acid ([HA]):
From the question, we know that the initial volume of acetic acid is 100.0 mL and the concentration is 1.0 M.
Now we can substitute the values into the Henderson-Hasselbalch equation:
pH = 4.75 + log (1.0 M / 1.0 M)
pH = 4.75 + log (1.0)
pH = 4.75 + 0
pH = 4.75
Therefore, the initial pH of Buffer C is 4.75.
To determine the initial pH of a buffer solution, you need to consider the acidic dissociation equilibrium of acetic acid and the basic hydrolysis equilibrium of sodium acetate. The pH of a buffer depends on the concentrations of the weak acid and its conjugate base. Here's how you can calculate the initial pH of Buffer C:
1. Write the equation for the dissociation of acetic acid:
CH3COOH ⇌ CH3COO- + H+
2. Determine the initial concentrations of acetic acid and acetate ion:
- Acetic acid (CH3COOH) is given as 1.0 M in 100.0 mL (0.1 L). This means the initial concentration of acetic acid is 1.0 M.
- The sodium acetate (CH3COONa) is produced from the reaction, and since 1 mole of sodium acetate is formed from 1 mole of acetic acid, the concentration of sodium acetate would also be 1.0 M.
3. Use the Henderson-Hasselbalch equation to calculate the pH of the buffer:
pH = pKa + log ([Salt]/[Acid])
- To find the pKa value for acetic acid, you can look it up in a reference table or use the acid dissociation constant (Ka) for acetic acid, which is 1.8 x 10^-5 at 25°C.
- Calculate the concentration ratio [Salt]/[Acid] by dividing the concentration of sodium acetate by the concentration of acetic acid.
pH = pKa + log (1.0 M/1.0 M)
4. Calculate the pH:
- Substitute the values into the equation and solve for the initial pH.
Now, you can use this information and perform the calculations to determine the initial pH of Buffer C.