Describe the preparation of 40 liters of 0.02 m phosphate buffer, ph 6.9

The preparation of 40 liters of 0.02 m phosphate buffer, ph 6.9, may be carried out by adding 132g of solid trisodium phosphate to 1290ml of hydrochloric acid (HCl concentration 1 mol/L), then making up to a final liquid volume of 40 liters by adding water. Method: Weigh out 132 grams of Na3PO4 (s), and add it to 1290 ml 1M HCl (l). Mix, then add water, to a final volume of 40 liters.