1. Start with Sodium Hydroxide (NaOH):

Take a concentrated solution of sodium hydroxide (NaOH), also known as caustic soda. This serves as the source of sodium ions for the reaction.

2. Add Phosphoric Acid (H3PO4):

Gradually add phosphoric acid (H3PO4) to the sodium hydroxide solution. Phosphoric acid provides the phosphate ions required for the formation of disodium phosphate.

3. Adjust the pH:

Maintain the pH of the mixture around 8.5 to 9.0 by carefully adding either sodium hydroxide or phosphoric acid as needed. This pH range is important for the precipitation of disodium phosphate.

4. Heat the Solution:

Gently heat the mixture to a temperature between 30 and 40 degrees Celsius (86 to 104 degrees Fahrenheit). This helps enhance the dissolution and reaction of the components.

5. Crystallization:

As the solution cools, sodium phosphate will start to crystallize. Let the solution sit undisturbed for several hours or overnight to allow complete crystallization.

6. Filter and Wash:

Filter the crystallized disodium phosphate using a Buchner funnel and filter paper. Wash the crystals thoroughly with cold water to remove any impurities.

7. Dry the Crystals:

Transfer the filtered disodium phosphate crystals to a clean tray or dish. Place it in a warm, well-ventilated area or an oven at a low temperature (around 50 degrees Celsius or 122 degrees Fahrenheit) to dry completely.

Once the crystals are completely dry, you will have obtained disodium phosphate (Na2HPO4). Store the disodium phosphate in an airtight container to prevent moisture absorption and maintain its quality.

Note: Always wear appropriate safety gear, including gloves, eye protection, and a lab coat, when handling chemicals.