3.4.2.2 Calcium carbonate content in soil Place 5 to 25grams of soil in a 150 ml beaker, add 50 ml of reagent A by means of a pipette, cover with a watch glass, and boil gently for 5 min. Cool, filter and wash all the acid from the soil with water. Determine the amount of unused acid by adding 2 drops of 1% phenolphthalein and back-titrating with 0.25 N of NaOH