Disodium phosphate Stock Solution

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Stock Solution Preparation Guide – Sodium Phosphate Dibasic

A 1 M sodium phosphate dibasic stock solution can be prepared from sodium phosphate dibasic dihydrate (Na₂HPO₄·2H₂O). This solution is commonly used as a component in phosphate buffer systems or other biological applications requiring phosphate ions.

Chemical Information

Name	Molecular Formula	Molecular Weight	CAS
Disodium phosphate (anhydrous)	Na₂HPO₄	141.96 g/mol	7558-79-4
Disodium phosphate dihydrate	Na₂HPO₄·2H₂O	177.99 g/mol	10028-24-7
Disodium phosphate heptahydrate	Na₂HPO₄·7H₂O	268.07 g/mol	7782-85-6
Disodium phosphate dodecahydrate	Na₂HPO₄·12H₂O	358.14 g/mol	10039-32-4

Preparation of 1 M Sodium Phosphate Dibasic

To prepare 1000 mL of 1 M sodium phosphate dibasic solution:

Weigh out 177.99 g of sodium phosphate dibasic dihydrate (Na₂HPO₄·2H₂O).
Transfer the solid to a 2 L beaker or flask.
Add ~800 mL of deionized or distilled water and stir until completely dissolved.
Adjust the volume to 1000 mL with deionized water and mix thoroughly.
Solution will appear clear and colorless.
If needed for sterile applications, transfer to an autoclavable bottle and autoclave (20 min at 121–124 °C, liquid cycle).

Notes and Precautions

The hydrated dibasic phosphate is hygroscopic and may absorb water; adjust the weighed mass accordingly if necessary.
Do not dissolve solid directly into 1000 mL water; large solute addition can increase final volume.
Wear appropriate personal protective equipment (lab coat, gloves, goggles).

Storage and Usage

The prepared 1 M solution can be stored at room temperature when not in use.
This stock is commonly used to prepare phosphate buffer solutions when mixed with monosodium phosphate stock at desired ratios.