To make 1 L of 0.2 M sodium phosphate buffer at pH 7.0, you will need the following:

- 27.8 g of sodium dihydrogen phosphate (NaH2PO4)

- 35.6 g of disodium hydrogen phosphate (Na2HPO4)

- 1 L of deionized water

Instructions:

1. Dissolve the sodium dihydrogen phosphate in approximately 500 mL of deionized water.

2. Dissolve the disodium hydrogen phosphate in approximately 500 mL of deionized water.

3. Combine the two solutions and mix well.

4. Adjust the pH of the buffer using a pH meter and a small amount of concentrated hydrochloric acid (HCl) or sodium hydroxide (NaOH) if necessary.

5. Add more deionized water to reach a final volume of 1 L.

6. Mix the buffer thoroughly to ensure uniformity.

The final solution will be 0.2 M sodium phosphate buffer at pH 7.0, suitable for various biological applications.