I need 1L of a pH 4 buffer with a total molarity of 1. Propose a buffer system and a recipe to achieve this goal. (acetic acid/acetate would probably be a good choice.) help please!
To create a 1L pH 4 buffer with a total molarity of 1, using acetic acid and acetate as the buffer system is indeed a good choice. Here's how you can achieve this:
1. Calculate the required amounts of acetic acid and sodium acetate.
- First, determine the desired ratio of the concentrations of acetic acid (HA) to acetate (A-) in the buffer solution. A common ratio is 1:1 for maximum buffering capacity.
- Let's assume you want a final concentration of 0.5 M for both acetic acid and sodium acetate since their initial concentrations will be the same.
- The total molarity of the buffer will be the sum of the acetic acid and sodium acetate concentrations, which is 1 M in this case.
2. Calculate the amounts of acetic acid and sodium acetate needed:
- The molar mass of acetic acid is CH3COOH: 60.05 g/mol.
- The molar mass of sodium acetate is CH3COONa: 82.03 g/mol.
- To make a 1L solution of 0.5 M acetic acid, you would need 0.5 moles (0.5 M x 1 L = 0.5 moles).
- Similarly, you would need 0.5 moles of sodium acetate.
3. Convert the moles to grams:
- For acetic acid: 0.5 moles x 60.05 g/mol = 30.025 grams.
- For sodium acetate: 0.5 moles x 82.03 g/mol = 41.015 grams.
4. Prepare the buffer solution:
- Dissolve 30.025 grams of acetic acid in some distilled water (less than 1L) in a beaker.
- Add 41.015 grams of sodium acetate to the same beaker.
- Stir the solution until both solutes are completely dissolved.
- Once dissolved, transfer the solution to a 1L volumetric flask.
- Fill the remaining volume of the flask with distilled water to reach the 1L mark.
5. Adjust the pH:
- Measure the pH of the buffer solution using a pH meter or pH indicator paper.
- If the pH is not exactly 4, you can adjust it by adding small amounts of either acetic acid or sodium acetate.
- For a higher pH, add acetic acid dropwise and stir until the desired pH is reached.
- For a lower pH, add sodium acetate dropwise and stir until the desired pH is achieved.
- Remember to measure the pH after each addition to avoid overshooting the target pH of 4.
By following these steps, you can prepare a 1L pH 4 buffer using the acetic acid/acetate buffer system with a total molarity of 1.