The molar mass of phosphoric acid (H3PO4) is 97.994 g/mol. To prepare 1L of a 0.025M solution of phosphoric acid, you will need:

0.025 M = (0.025 mol/L)/(97.994 g/mol) = 2.44e-3 mol

Step 2: Weigh out the phosphoric acid

Using a pipette, weigh out 0.239 g of phosphoric acid.

Step 3: Dissolve the phosphoric acid in a small amount of water

Add the phosphoric acid to 100 mL of deionized water in a beaker. Stir until the acid is completely dissolved.

Step 4: Transfer the solution to a volumetric flask and add more water

Pour the phosphoric acid solution into a 1L volumetric flask. Add more deionized water until the total volume of the solution reaches 1L. Mix thoroughly.

Step 5: Verify the concentration of the solution

To verify the concentration of the solution, you can use a pH meter or a conductivity meter. The pH of the prepared 0.025M phosphoric acid solution should be approximately 1.52, which corresponds to the expected concentration.