Describe the procedure for preparing 250mL of buffer solution with a pH of 5.00 from acetic acid (CH3COOH) and sodium acetate. How many grams of acid do you have to mix with 3.6 grams of sodium acetate? (Given Ka for acetic acid = 1.8x10^-5)
To prepare a buffer solution with a pH of 5.00 using acetic acid (CH3COOH) and sodium acetate, you can follow these steps:
Step 1: Calculate the moles of acetic acid:
- Determine the molar mass of acetic acid (CH3COOH):
- The molar mass of C = 12.01 g/mol
- The molar mass of H = 1.01 g/mol
- The molar mass of O = 16.00 g/mol
- The molar mass of CH3COOH = (12.01 x 2) + (1.01 x 4) + 16.00 = 60.05 g/mol
- Calculate the moles of acetic acid using its mass:
- Moles of acetic acid = Mass of acetic acid / Molar mass of acetic acid
- Moles of acetic acid = 3.6 g / 60.05 g/mol
Step 2: Calculate the moles of sodium acetate:
- Determine the molar mass of sodium acetate (CH3COONa):
- The molar mass of Na = 22.99 g/mol
- The molar mass of CH3COO = 59.04 g/mol
- The molar mass of CH3COONa = 22.99 + 59.04 = 82.03 g/mol
- Calculate the moles of sodium acetate using its mass:
- Moles of sodium acetate = Mass of sodium acetate / Molar mass of sodium acetate
- Moles of sodium acetate = 3.6 g / 82.03 g/mol
Step 3: Calculate the moles of acetic acid required to achieve the desired pH:
- The Henderson-Hasselbalch equation for a buffer solution is:
- pH = pKa + log(base/acid)
- Rearranging the equation to solve for base/acid:
- base/acid = 10^(pH - pKa)
- In this case, the desired pH is 5.00 and the pKa of acetic acid is 1.8x10^-5 (or -log10(1.8x10^-5)).
- base/acid = 10^(5.00 - (-log10(1.8x10^-5)))
- Calculate the ratio of the base to acid:
- base/acid = 10^(5.00 - (-log10(1.8x10^-5)))
Step 4: Calculate the moles of acid needed to prepare the buffer solution:
- Multiply the moles of acetic acid calculated in Step 1 by the ratio of the base to acid obtained in Step 3.
- Moles of acid needed = Moles of acetic acid x (base/acid ratio)
Step 5: Calculate the grams of acid needed:
- Multiply the moles of acid needed by the molar mass of acetic acid.
- Grams of acid needed = Moles of acid needed x Molar mass of acetic acid
To summarize, follow these steps to prepare 250 mL of buffer solution with a pH of 5.00 using acetic acid and sodium acetate:
1. Calculate the moles of acetic acid.
2. Calculate the moles of sodium acetate.
3. Calculate the ratio of base/acid using the Henderson-Hasselbalch equation.
4. Calculate the moles of acid needed using the ratio and moles of acetic acid.
5. Calculate the grams of acid needed using the moles of acid and molar mass of acetic acid.
Additionally, I cannot provide the exact value for the base/acid ratio or the exact amount of grams of acid needed without more information regarding the concentration or volume of the sodium acetate solution you have.
To prepare a buffer solution with a specific pH, you need to mix a weak acid with its conjugate base or a weak base with its conjugate acid. In this case, we are given that we need to prepare a buffer solution with a pH of 5.00 using acetic acid (CH3COOH) and sodium acetate.
To determine the amount of acetic acid and sodium acetate needed, we can use the Henderson-Hasselbalch equation:
pH = pKa + log ([A-]/[HA])
First, let's calculate the pKa value of acetic acid. The given Ka for acetic acid is 1.8x10^-5. To determine the pKa, we use the equation pKa = -log(Ka):
pKa = -log(1.8x10^-5) = 4.74
Next, we can substitute the given pH, pKa, and the concentrations of the acetic acid and sodium acetate to solve for the ratio [A-]/[HA]:
5.00 = 4.74 + log ([A-]/[HA])
0.26 = log ([A-]/[HA])
Now, we know that a buffer is typically prepared with equal amounts of acid and its conjugate base. This means that [A-] and [HA] are equal. Therefore, we can substitute [A-] = [HA] into the equation:
0.26 = log (1)
From the equation, log (1) = 0, thus:
0.26 = 0
Since this is not possible, it means that it is not possible to prepare a buffer solution with a pH of 5.00 using acetic acid and sodium acetate.
As for the second part of the question, i.e., how many grams of acid should be mixed with 3.6 grams of sodium acetate, since we can't prepare the desired buffer solution, we cannot determine the exact amount of acid to be mixed.