HEPES, is a commonly used component of physiological buffers. The PKa of the protonated amino group of HEPES is 7.55 at 25C.
Describe the preparation of 1.00L of 0.100M HEPES buffer, pH 8.00, from the sodium salt of the basic form of HEPES (MW 260.3), .0M HCL and deionized water
The conc is 6.0M HCL
To prepare a 1.00L of 0.100M HEPES buffer with a pH of 8.00, you will need the sodium salt of the basic form of HEPES, 0.1M HCl, and deionized water. Here's a step-by-step guide to the preparation:
Step 1: Calculate the amount of HEPES required:
The molecular weight (MW) of HEPES is given as 260.3 g/mol (grams per mole). To prepare a 0.100M solution, you need to calculate the mass of HEPES required.
Mass = Molarity * Volume * MW
Mass = 0.100 mol/L * 1.00 L * 260.3 g/mol
Step 2: Prepare the HEPES solution:
Weigh out the calculated mass of HEPES and dissolve it in a small volume of deionized water. Make sure the HEPES is completely dissolved.
Step 3: Adjust the pH using HCl:
To achieve a pH of 8.00, you need to adjust the pH of the solution using 0.1M HCl. The pKa of the protonated amino group of HEPES is given as 7.55. This means that the optimal pH for HEPES buffering capacity is around 7.55. In this case, as we want a slightly higher pH, we will need to decrease the acidity by adding HCl.
The HEPES buffer has a basic form, so to adjust the pH to 8.00, you need to add drops of 0.1M HCl to decrease the pH. After each addition, you should measure the pH using a pH meter until you reach pH 8.00. Keep in mind that diluting the solution slightly by adding drops of 0.1M HCl will not significantly affect the final concentration.
Step 4: Adjust the volume:
Once the desired pH of 8.00 is achieved, adjust the volume of the solution using deionized water. Use a graduated cylinder or a volumetric flask to measure and add water until you reach a final volume of 1.00L.
Step 5: Mix and validate:
Thoroughly mix the solution to ensure the HEPES buffer is homogenous. Finally, validate the pH using a pH meter to confirm that it remains at 8.00.
Note: It's important to handle chemicals and equipment safely, follow good laboratory practices, and use accurate measuring tools for precise results.