While the question specifically asks about calcium phosphate, the provided reference details the reaction of calcium phosphide with water. These are two distinct chemical compounds with different properties regarding their reaction with water. Calcium phosphate (e.g., Ca₃(PO₄)₂) is generally insoluble and does not react with water in the manner described for phosphides. The information below pertains to the reaction of calcium phosphide with water, as per the reference.
When calcium phosphide (Ca₃P₂) reacts with water, it undergoes a vigorous reaction to produce phosphine gas (PH₃) and calcium hydroxide (Ca(OH)₂). This reaction is a well-known method for generating phosphine, a highly toxic and flammable gas.
Understanding the Reactants: Calcium Phosphate vs. Calcium Phosphide
It's crucial to distinguish between these two compounds:
- Calcium Phosphate (Ca₃(PO₄)₂): A salt of calcium and the phosphate ion. It is a primary component of bones and teeth and is generally stable and largely insoluble in water. It does not react with water to produce phosphine or calcium hydroxide in the way calcium phosphide does.
- Calcium Phosphide (Ca₃P₂): A compound of calcium and phosphorus, where phosphorus is in the -3 oxidation state (as phosphide, P³⁻). It reacts readily with water and acids due to the strong basicity of the phosphide ion.
The Reaction of Calcium Phosphide with Water
According to the provided reference, the interaction between calcium phosphide and water yields two main products:
- Phosphine (PH₃): A colorless, highly toxic, and flammable gas with a characteristic garlic or decaying fish odor. It can auto-ignite in air.
- Calcium Hydroxide (Ca(OH)₂): A white solid, commonly known as slaked lime, which is sparingly soluble in water, forming a basic solution.
The chemical equation for this reaction is:
Ca₃P₂(s) + 6H₂O(l) → 2PH₃(g) + 3Ca(OH)₂(aq/s)
Key Characteristics and Practical Insights
- Vigorous Reaction: The reaction of calcium phosphide with water is typically very vigorous and exothermic, releasing heat.
- Phosphine Production: This reaction is a laboratory or industrial method for preparing phosphine gas. The reference also notes that phosphine can be prepared by reacting white phosphorus with concentrated sodium hydroxide, or by reacting calcium phosphide with dilute acid.
- Example: Fishing boats sometimes use calcium phosphide flares (often mixed with calcium carbide) for navigation, where contact with water releases phosphine (and acetylene from carbide), which ignites spontaneously in air, producing a bright flame.
- Safety Considerations: Due to the toxicity and flammability of phosphine gas, handling calcium phosphide and conducting this reaction requires strict safety protocols, including good ventilation and fire precautions.
Comparison Table: Calcium Phosphate vs. Calcium Phosphide
| Feature | Calcium Phosphate (e.g., Ca₃(PO₄)₂) | Calcium Phosphide (Ca₃P₂) |
|---|---|---|
| Common Uses | Bones, teeth, fertilizers | Source of phosphine, rodenticides, signal flares |
| Water Reactivity | Largely insoluble; inert | Highly reactive; produces phosphine and calcium hydroxide |
| Products with Water | No significant reaction | Phosphine (PH₃) and Calcium Hydroxide (Ca(OH)₂) |
| Toxicity of Products | Non-toxic products | Highly toxic and flammable phosphine gas |
In summary, while the question mentioned calcium phosphate, the provided information specifically details the reaction of calcium phosphide with water, producing phosphine and calcium hydroxide. This highlights the importance of precise chemical nomenclature in understanding reactivity.
