Calcium hydroxide Ca(OH)2 CAS 1305-62-0

Physical and Chemical Properties

Calcium hydroxide, an inorganic compound with the chemical formula Ca(OH)₂, commonly known as slaked lime or hydrated lime. It is a white powdery solid that, when added to water, separates into two layers: the upper aqueous layer is called clear lime water, and the lower suspension is known as lime milk or lime slurry. The clear supernatant, lime water, can be used to test for carbon dioxide, while the turbid lower layer, lime milk, serves as a building material. The solubility of calcium hydroxide decreases as temperature increases. It is insoluble in alcohol, soluble in ammonium salts and glycerol, and reacts with acids to form corresponding calcium salts. At 580°C, it decomposes into calcium oxide and water.

Calcium hydroxide is a strong base with bactericidal and preservative properties, and it is corrosive to skin and fabrics. However, due to its limited solubility, it is less hazardous than strong bases like sodium hydroxide. Calcium hydroxide has wide industrial applications. It is commonly used as a building material, as well as a disinfectant and chemical raw material.

Solubility in Water (g/100ml)

Grams dissolved per 100 milliliters of water at different temperatures (°C):

0.189g/0°C; 0.182g/10°C; 0.173g/20°C; 0.16g/30°C; 0.141g/40°C; 0.121g/60°C; 8.6×10⁻²/80°C; 7.6×10⁻²/90°C

Identification Test

Mix the sample with 3 to 4 times its weight of water to form a uniform paste. After standing to clarify, the transparent supernatant turns litmus alkaline. Dissolve 1g of the sample in 20ml of water, add sufficient acetic acid to form a solution, and the calcium salt test (IT-10) will be positive.

Chemical Properties

Fine white powder

Uses

Used in the production of bleaching powder, water softeners, disinfectants, and clarifiers for tap water, as well as in the construction industry and pharmaceuticals.

Can serve as an additive in rubber and petroleum industries, preventing coking, sludge deposition, and neutralizing corrosion in lubricants.

Also used as a water softener, disinfectant, acid neutralizer, etc.

Employed as an analytical reagent, carbon dioxide absorbent, and in organic synthesis. Used in the production of bleaching powder, water softeners, depilatory agents, disinfectants, antacids, astringents, and various calcium salts. Used to test for carbon dioxide and gas absorption.

Leather depilation, insecticide, water treatment.

Production Method

Lime slaking method: After calcining limestone into calcium oxide, it is carefully selected and mixed with water in a ratio of 1:(3–3.5) for slaking, producing a calcium hydroxide slurry. The slurry is purified, separated from residues, centrifugally dehydrated, dried at 150–300°C, and screened (120 mesh or finer) to obtain the final calcium hydroxide product.

CaCO₃ → CaO + CO₂↑

CaO + H₂O → Ca(OH)₂

Category

Pesticide

Toxicity Grade

Low toxicity

Acute Toxicity

Oral - Rat LD₅₀: 7340 mg/kg;

Oral - Mouse LD₅₀: 7300 mg/kg

Irritation Data

Eye - Rabbit 10 mg Severe

Flammability Hazard Characteristics

Non-flammable, but a public nuisance dust

Storage and Transportation Characteristics

Store in a cool, ventilated, dry warehouse

Fire Extinguishing Agents

Water, carbon dioxide, foam, dry powder