How would you prepare a buffer (100ml) of pH 6.8 and concentration 0.1M given solid imidazole (mol wt.=68) and concentrated HCl
To prepare a buffer of pH 6.8 and concentration 0.1M using solid imidazole and concentrated HCl, you need to follow a step-by-step procedure:
1. Calculate the amount of imidazole required:
- Determine the number of moles needed by multiplying the desired concentration by the volume of the buffer.
Number of moles = Concentration (M) × Volume (L)
Number of moles = 0.1 M × 0.1 L = 0.01 moles
- Calculate the mass of imidazole required using its molar mass.
Mass (g) = Number of moles × Molar mass (g/mol)
Mass (g) = 0.01 mol × 68 g/mol = 0.68 g
2. Dissolve the calculated amount of imidazole in a small volume of distilled water.
- Weigh out 0.68 grams of solid imidazole using a balance.
- Add the imidazole to a beaker or flask.
- Gradually add distilled water while stirring until the solid imidazole dissolves completely.
3. Adjust the pH of the solution using concentrated HCl:
- Concentrated HCl is a strong acid, so it will react with imidazole and protonate it, lowering the pH.
- Add a few drops of concentrated HCl to the imidazole solution.
- Stir the solution and check the pH using a pH meter or pH indicator strips.
- Repeat the addition of HCl and pH measurement until the desired pH of 6.8 is achieved.
4. Adjust the total volume of the solution to 100 ml:
- Transfer the imidazole-HCl solution to a volumetric flask.
- Use distilled water to rinse the original container and transfer any remaining solution into the volumetric flask.
- Add distilled water to the volumetric flask until the final volume reaches 100 ml. Mix well.
5. Verify the pH and concentration:
- Use a pH meter or pH indicator strips to confirm that the pH of the buffer is 6.8.
- Measure the concentration of the buffer solution using appropriate analytical techniques, such as titration or spectroscopy, to ensure it matches the desired 0.1M concentration.
By following these steps, you can prepare a 100 ml buffer solution with a pH of 6.8 and concentration of 0.1M using solid imidazole and concentrated HCl.
What's the pKa?
You have two equations.
#1 is pH = pKa + log (base)/(acid)
6.8 = pKa + log b/a
#2 is a + b = 0.1
Solve these two equations for (acid) and (base).
Calculate grams base needed, add to 100 mL of water, place in a pH meter, add HCl to the desired pH.