How can i prepare a 100ml, 0.1M phosphate buffer solution (pH = 7) out of Na2HPO4 and NaH2PO4

To prepare a 100ml, 0.1M phosphate buffer solution with a pH of 7 using Na2HPO4 and NaH2PO4, you need to calculate the quantities of each compound required.

Here's how you can do it:

Step 1: Determine the pH range for the buffer solution
Since you want a pH of 7, which is close to the pKa of the phosphate buffer system (pKa ≈ 7.2), the buffer will be most effective. This means that you can use a 1:1 ratio of Na2HPO4 and NaH2PO4.

Step 2: Calculate the molar concentration of each compound:
The molar concentration needed for a 0.1M buffer solution is the same for both Na2HPO4 and NaH2PO4. So, each compound should be present at a concentration of 0.05M.

Step 3: Calculate the moles of each compound required:
To determine how many moles of Na2HPO4 and NaH2PO4 you need, multiply the molar concentration by the desired volume:
moles = molar concentration × volume (in liters)

moles of Na2HPO4 = 0.05M × 0.1L = 0.005 moles
moles of NaH2PO4 = 0.05M × 0.1L = 0.005 moles

Step 4: Convert moles to grams:
To convert moles to grams, you need the molar mass of each compound.
The molar mass of Na2HPO4 is approximately 141.96 g/mol.
The molar mass of NaH2PO4 is approximately 119.98 g/mol.

mass of Na2HPO4 = moles × molar mass = 0.005 moles × 141.96 g/mol ≈ 0.71 grams
mass of NaH2PO4 = moles × molar mass = 0.005 moles × 119.98 g/mol ≈ 0.60 grams

Therefore, you need approximately 0.71 grams of Na2HPO4 and 0.60 grams of NaH2PO4 to prepare a 100ml, 0.1M phosphate buffer solution with a pH of 7.

Note: Be sure to accurately measure the masses of the compounds and dissolve them in the appropriate volume of water to ensure accurate preparation of the buffer solution.