What happens when you mix Calcium Hydroxide and Sulphuric acid?

Calcium hydroxide, Ca(OH)₂, better known as slaked lime, is a strong base. It is produced when quicklime reacts with water and is widely used in construction, agriculture, and water treatment. Because of its alkalinity, it neutralizes acids efficiently, creating salts that are useful in many industries.

With Phosphoric Acid

Phosphoric acid (H₃PO₄) is a weak acid frequently used in fertilizers, beverages, and food technology. When mixed with calcium hydroxide, the following reaction occurs:

3Ca(OH)₂ + 2H₃PO₄ → Ca₃(PO₄)₂ + 6H₂O

The product, tricalcium phosphate (Ca₃(PO₄)₂), is insoluble and precipitates as a white solid. It is valued as a food additive to supply calcium and as a fertilizer to provide phosphorus for plant growth. This neutralization shows how acid–base chemistry produces compounds with nutritional and agricultural value.

With Sulphuric Acid

Sulphuric acid (H₂SO₄), one of the strongest mineral acids, reacts vigorously with calcium hydroxide:

Ca(OH)₂ + H₂SO₄ → CaSO₄ + 2H₂O

The reaction is highly exothermic. The resulting salt, calcium sulphate (CaSO₄), appears in hydrated form as gypsum (CaSO₄·2H₂O). Gypsum is essential for making cement, plaster, and drywall. This neutralization is also applied in treating acid waste streams safely.

Comparison of Both Reactions

Industrial Importance

• Food and Agriculture: Tricalcium phosphate improves calcium levels in food and provides phosphorus in fertilizers.
• Construction: Gypsum is indispensable for plaster, cement, and drywall production.
• Environmental Protection: Calcium hydroxide neutralizes acid waste, helping maintain safe pH in industrial effluents.

Safety Notes

Both reactions release heat, and concentrated acids can cause serious burns. When handling calcium hydroxide with phosphoric or sulphuric acid, protective equipment—gloves, goggles, and proper ventilation—is essential. Reactions should be carried out slowly with good mixing to avoid splashing and overheating.

Conclusion

Calcium hydroxide reacts with phosphoric acid to form tricalcium phosphate and with sulphuric acid to produce calcium sulphate. These neutralization reactions create salts with wide industrial applications. From food technology to construction, their products remain vital, provided they are handled with appropriate safety measures.