Describe how to prepare 10 mL of 0.200 acetate buffer, pH 5.00, starting with pure acetic acid and solutions containg 3 M HCl and 3 M NaOH. Include both quantitate and qualitative details.
I know that a strong base reacts completely witha weak acid because the equilibrium constant in large. and that pH=pka + log ([NaOH]/[HCl])
acetate is the base. You need NaOH with HAc (acetic acid). You don't need the HCl.
pH = pKa + log (base)/(acid)
5.00 = pKa + log b/a. Look up pKa for HAc.
Solve for b/a ratio. That's eqn 1.
Equation 2 is b + a = 0.200
Solve those two equations simultaneously for b and a.
I prefer to work in millimols. You want 10 mL x 0.2M = 2 mmols.
Solving the equations give you base = 1.27 mmols and acid = 0.73 mmols.
.......HAc + OH^- ==> Ac^- + H2O
I.......2.....0........0.......
add..........1.27..............
C....-1.27..1.27.....1.27......
E......0.73..0.......1.27
So you want 0.73 mmols HAc and you want to add 1.27 mmols of 3M NaOH. M = mmols/mL or mL = mmols/M
mL NaOH = 1.27/3M = 0.423 mL
Pure HAc is 17 M. Solve the same way to see mL pure HAc. I have 0.118 mL
YOU SHOULD PLUG THOSE NUMBERS INTO THE HH EQUATION AND CONFIRM THAT IT GIVES YOU A Ph OF 5.00.
So you start with 0.118 mL of pure HAc, add 0.423 mL of 3M NaOH, make to slightly less than the mark of a 10 mL volumetric flask and check the pH. Add 3M NaOH or 3M HCl (small amounts) until the pH reads 5.00, then make to the mark of the volumetric flask. Mix thoroughly.
how do you prepare 100 mL of 0.200 M acetate buffer, pH5.00, starting with pure liquid acetic acid and solutions containing~3 M HCl and ~3 M NaOH
how to sagot that one huhu
To prepare a 10 mL acetate buffer with a pH of 5.00, starting with pure acetic acid, 3 M HCl, and 3 M NaOH, follow these quantitative and qualitative steps:
Quantitative Steps:
1. Calculate the amount of acetic acid needed:
- First, determine the concentration of the acetate buffer. In this case, it is 0.200 M.
- Next, determine the desired volume of the buffer solution, which is 10 mL.
- Multiply the concentration by the volume to find the moles of acetic acid needed: 0.200 M × 0.010 L = 0.002 moles.
2. Calculate the amount of sodium acetate needed:
- Since acetic acid acts as a weak acid and sodium acetate is its conjugate base, we need to prepare an acetate buffer by combining them.
- The buffer solution formula is: CH3COOH + CH3COONa.
- The ratio of acetic acid to sodium acetate will depend on the pH desired. By using the Henderson-Hasselbalch equation, pH = pKa + log([A-]/[HA]), we can determine this ratio.
- In this case, pH = 5.00, and acetic acid's pKa is around 4.75. By substituting these values, we can calculate the desired ratio of [A-] (acetate ion) to [HA] (acetic acid) in the buffer.
3. Calculate the amount of HCl needed:
- Since acetic acid reacts with HCl, you will need to neutralize it. However, since HCl is strong, it will completely react with acetic acid.
- Calculate the moles of HCl required to neutralize all the acetic acid. Use the stoichiometry of the neutralization reaction to find the moles of HCl.
4. Calculate the amount of NaOH needed:
- Acetic acid is a weak acid, which means that not all of it will react with NaOH. Use the stoichiometry of the reaction between acetic acid and sodium hydroxide to find the amount of NaOH needed.
Qualitative Steps:
1. Using a laboratory-grade balance, accurately weigh out the calculated amount of acetic acid and transfer it to a clean, dry beaker.
2. Gradually add distilled water to the beaker, stirring gently to dissolve the acetic acid. This will help prepare a solution with the desired concentration.
3. In a separate beaker or flask, accurately measure the calculated amount of sodium acetate. Add distilled water to dissolve the sodium acetate completely.
4. Add the dissolved sodium acetate solution to the beaker containing the acetic acid solution. Stir gently to mix the solutions thoroughly.
5. To neutralize any excess acetic acid, slowly add the calculated amount of 3 M HCl with stirring. Continue adding HCl drop by drop until the pH of the solution reaches 5.00. Measure the pH using a pH meter or pH indicator paper.
6. To adjust the pH, either raise or lower it, add either 3 M HCl or 3 M NaOH in small increments as needed, while stirring and checking the pH after each addition. Repeat this process until the desired pH of 5.00 is achieved.
7. Once the desired pH is reached, transfer the buffer solution to a clean, sterile container, such as a vial or bottle, for storage or further use.
By following these quantitative and qualitative steps, you can prepare a 10 mL acetate buffer solution with a pH of 5.00 using the provided starting materials.