When calcium oxide (CaO), also known as quicklime, reacts with phosphoric acid (H₃PO₄), a neutralization reaction takes place, primarily producing calcium phosphate (Ca₃(PO₄)₂) and water (H₂O). This reaction exemplifies how a basic oxide reacts with an acid.
Calcium oxide is a basic oxide, meaning it reacts with acids. While the provided chemical reference specifically highlights the reaction of phosphoric acid with calcium hydroxide (Ca(OH)₂), a strong base, it's important to understand the connection. In an aqueous environment, calcium oxide readily reacts with water to form calcium hydroxide (Ca(OH)₂).
As stated in chemical principles, "phosphoric acid, H₃PO₄, a weak acid, will react with calcium hydroxide, Ca(OH)₂, a strong base, to produce calcium phosphate, Ca₃(PO₄)₂, an insoluble salt, and water." This describes the common outcome when a calcium-based compound reacts with phosphoric acid. Whether calcium oxide is first converted to calcium hydroxide in water or reacts directly as a basic oxide, the end products remain the same under conditions that favor the formation of the normal salt.
The Chemical Reaction
The balanced chemical equation for the reaction of calcium oxide with phosphoric acid to form calcium phosphate and water is:
3CaO(s) + 2H₃PO₄(aq) → Ca₃(PO₄)₂(s) + 3H₂O(l)
This equation shows that three moles of solid calcium oxide react with two moles of aqueous phosphoric acid to yield one mole of solid calcium phosphate and three moles of liquid water.
Products of the Reaction
The two main products formed are:
- Calcium Phosphate (Ca₃(PO₄)₂): This is an insoluble salt. Its insolubility means it will precipitate out of the solution as a solid. Calcium phosphate is a vital component of bones and teeth and has various industrial uses.
- Water (H₂O): A common byproduct of acid-base neutralization reactions.
Key Characteristics of the Reaction
| Reactant 1 | Reactant 2 | Product 1 | Product 2 | Reaction Type | Product Solubility |
|---|---|---|---|---|---|
| Calcium Oxide (CaO) | Phosphoric Acid (H₃PO₄) | Calcium Phosphate (Ca₃(PO₄)₂) | Water (H₂O) | Neutralization | Insoluble |
- Acid-Base Nature: Calcium oxide acts as a base (specifically, a basic oxide) and phosphoric acid acts as an acid.
- Insoluble Product: The formation of insoluble calcium phosphate makes this a precipitation reaction if the reactants are in solution.
- Heat Release: Neutralization reactions are typically exothermic, meaning they release heat.
Practical Applications and Insights
The reaction between calcium compounds and phosphoric acid is significant in several fields:
- Fertilizer Production: Calcium phosphate, particularly in modified forms like superphosphate, is a key ingredient in agricultural fertilizers, providing essential phosphorus for plant growth. The reaction with phosphoric acid is a step in processing phosphate rock (which contains impure calcium phosphate) into more soluble forms.
- Water Treatment: In some water treatment processes, calcium compounds can be used to react with phosphates, helping to remove them from wastewater to prevent eutrophication.
- Dental Health: Calcium phosphate compounds are widely used in dental products, such as toothpastes and remineralizing agents, to strengthen tooth enamel and prevent decay.
- Biomaterials: Due to its biocompatibility, calcium phosphate is extensively used in biomaterials for bone regeneration and implants.
Understanding this reaction is fundamental in chemistry, particularly in inorganic and industrial applications, showcasing the versatile nature of calcium compounds and phosphoric acid.
