Making sodium hydrogen phosphate involves a chemical reaction between a sodium source and phosphoric acid under controlled conditions. A specific method utilizes sodium hydrogen carbonate and phosphoric acid to synthesize disodium hydrogen phosphate.
One method for preparing sodium hydrogen phosphate involves the controlled reaction between sodium hydrogen carbonate (NaHCO₃) and phosphoric acid (H₃PO₄). This process carefully manages temperature and pH to ensure the formation of the desired product.
Preparation Method
The method described involves a specific sequence of steps to achieve the desired chemical reaction and product characteristics.
Reaction Overview
This preparation is essentially a neutralization reaction between the slightly alkaline sodium hydrogen carbonate and the acidic phosphoric acid. The goal is to produce sodium hydrogen phosphate, water, and carbon dioxide gas (which is released). The specific sodium hydrogen phosphate formed depends on the molar ratio of reactants and the final pH. The given conditions (pH 8.7-9.2) strongly indicate the formation of disodium hydrogen phosphate (Na₂HPO₄).
The general reaction can be simplified as:
NaHCO₃ + H₃PO₄ → Sodium Hydrogen Phosphate + H₂O + CO₂
Step-by-Step Process
The preparation method comprises the following steps:
- Slow Addition: Slowly add sodium hydrogen carbonate (NaHCO₃) into a phosphoric acid (H₃PO₄) solution. This slow addition helps control the reaction rate and prevent excessive foaming from the release of carbon dioxide.
- Neutral Reaction: Carry out the neutralization reaction between the two substances.
- Temperature Control: Control the reaction temperature within a specific range, holding it at 80-100 °C for a duration of 2 hours. Maintaining this temperature range is crucial for the reaction's efficiency and product formation.
- pH Control: During the reaction, control the pH value to be within the range of 8.7-9.2. This pH range is characteristic of solutions containing disodium hydrogen phosphate, indicating the desired degree of neutralization has been achieved.
- Natural Cooling: After the reaction and temperature/pH controls are complete, allow the mixture to naturally cool down. This step prepares the product for subsequent processing (like crystallization or drying, though not detailed in the reference).
Key Reaction Parameters
Controlling specific parameters is vital for the success of this synthesis method.
| Parameter | Value/Range | Duration | Notes |
|---|---|---|---|
| Reactants | NaHCO₃, H₃PO₄ | N/A | NaHCO₃ added slowly to H₃PO₄ |
| Reaction Type | Neutralization | N/A | Forms sodium hydrogen phosphate |
| Temperature | 80-100 °C | 2 hours | Crucial for reaction kinetics |
| Final pH | 8.7-9.2 | N/A | Ensures formation of desired product |
| Subsequent Step | Natural Cooling | N/A | Follows temperature/pH control |
These controlled conditions ensure that the reaction proceeds correctly to yield sodium hydrogen phosphate, specifically disodium hydrogen phosphate, at the desired purity and form.
What is Sodium Hydrogen Phosphate?
Sodium hydrogen phosphate is a generic term referring to sodium salts of phosphoric acid where one or two hydrogen atoms of the acid are replaced by sodium. The most common forms are monosodium phosphate (NaH₂PO₄), disodium hydrogen phosphate (Na₂HPO₄), and trisodium phosphate (Na₃PO₄). The method described, with a pH target of 8.7-9.2, is designed to produce disodium hydrogen phosphate (Na₂HPO₄). Disodium hydrogen phosphate is commonly used in food as an additive, in water treatment, and in chemical synthesis.
