How do i prepare KH2PO4-KOH buffer 0.2 M of pH 7.4?

To prepare a KH2PO4-KOH buffer of pH 7.4 with a concentration of 0.2 M, you will need to follow a series of steps. Here's a step-by-step guide:

Step 1: Calculate the molar concentration required.
To start, calculate the amount of KH2PO4 and KOH needed to achieve a concentration of 0.2 M.

Step 2: Convert molar concentration to grams.
Using the molar mass of KH2PO4 and KOH (136.09 g/mol and 56.11 g/mol, respectively), convert the molar concentration to grams. This will determine the amount of each substance needed.

Step 3: Prepare stock solutions.
Dissolve the calculated amount of KH2PO4 and KOH separately in distilled water to prepare two stock solutions.

Step 4: Adjust the pH.
Combine the stock solutions to achieve the desired pH of 7.4. To adjust the pH, you can use a pH meter or a suitable acid or base. In this case, KOH will raise the pH, while KH2PO4 will act as a buffer.

Step 5: Dilute the buffer.
If necessary, dilute the buffer solution to reach the desired final volume while maintaining the original concentration.

It's important to note that preparing buffers requires accurate measurements and precise calculations. Additionally, it is recommended to wear appropriate personal protective equipment (PPE) while handling chemicals and to ensure that the laboratory or workspace is well-ventilated.