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Ca(OH)2 is a colourless crystal or white powder of calcium hydroxide. It is also recognised as hydrated lime or slaked lime and is made by reacting calcium oxide (lime) with water in a process known as slaking. When subjected to heat above 580°C, it dehydrates, resulting in the formation of the oxide. It, like the oxide, has many applications, such as liming soil, refining sugar, and preparing other compounds. It is a strong base that is widely used as a low-cost alkali, often in the form of a suspension in water (milk of lime); that is used in leather tanning to remove hair from hides. It can be found in whitewash, mortar, and plaster. Because it is only mildly soluble in water (about 0.2 grams per 100 cubic centimeters), its solutions are mildly basic.
Reaction of calcium hydroxide
Calcium hydroxide, Ca(OH)2, is produced by mixing calcium oxide to water and forms colourless crystals (resulting in white powder) (calcium hydroxide is also called slaked lime). Calcium hydroxide is produced in massive quantities commercially through the thermal decomposition of limestone and the successive exothermic reaction of calcium oxide with water:
CaCO3 → CaO + CO2
CaO + H2O → Ca(OH)2 (+65.2 kJ)
The exothermic reaction of water produces enough energy to cause the water to evaporate.
Calcium hydroxide can be made in the laboratory by combining aqueous solutions of calcium chloride and sodium hydroxide:
CaCl2 + 2 NaOH → Ca(OH)2 + 2 NaCl
When calcium hydroxide is heated to 512 °C, it decomposes into calcium oxide and water:
Ca(OH)2 → CaO + H2O
Ca(OH)2 would be only slightly soluble in water (0.16g Ca(OH)2/100g water at 20°C), resulting in lime water, a basic solution. As the temperature rises, so does the solubility.
As the temperature rises, so does the solubility. Milk of lime is a water-based suspension of calcium hydroxide particles.
Due to the formation of calcium carbonate in the presence of carbon dioxide, lime water becomes milky:
Ca(OH)2 + CO2 → CaCO3 + H2O
Physical properties of calcium hydroxide
Ca(OH)2 has hexagonal crystalline structure.
This compound just isn’t very water soluble. However, its solubility decreases as temperature rises. Assume its dissolution rate at solubility is 1.73 g/L at 20°C and 1.89 g/L at 0°C
At temperatures close to its melting point, this compound also usually loses water and decomposes.
The calcium hydroxide solubility product (Ksp) can be calculated as 5.5 x 10-6.
It is a colourless white powder in solid state and known as slaked lime when hydrated.
Usage of calcium hydroxide
In past
Calcium hydroxide, which may seem a little outlandishly created in a laboratory to some and like something out of science fiction to others, is almost ubiquitous in daily life. It is obtained through a process that hydrates calcium oxide; in this reaction, the hydration of the lime generates heat, which aids in the drying and disinfection of the materials that are treated in many uses.
Calcium hydroxide-based products have a surprising number of applications. The truth is that slaked lime has been around since time immemorial, and with amazing results, such as in floor stabilisation (it was used in the development of the Great Wall of China), constructing (it was used, no more and no less, to build the Pyramid of Giza), and in addition to agriculture (the Celts used calcium hydroxide to fertilise fields, because much of their land had a poor or non-existent limestone content).
Now
Calcium hydroxide is used in the food industry to provide calcium and as a pH modifier, as well as in gas management due to its high efficacy in capturing acidic pollutants from manufacturing smoke and vapours.
It is also used as a feed additive to improve animal nutrition, and it is used in animal pens for its disinfecting power, which reduces the number of pathogenic organisms and viruses.
It can be used in the sugar industry to precipitate impurities and obtain pure sucrose.
It also helps with sludge treatment because it is an excellent aid in the elimination of microorganisms and bacteria while also neutralising bad odours.
Its properties are particularly beneficial in water treatment because it acts as a clarifier, coagulant, neutralizer, and precipitator of dissolved pollutants.
Conclusion
Hydrated lime, also recognised as calcium hydroxide or slaked lime, is a versatile material with intriguing properties that has significant benefits for industry, construction, and the environment as it can be used in a variety of ways. Calcium hydroxide (Ca(OH)2), also recognised as portlandite, slaked- or hydrated-lime, is widely used in a variety of industries and applications, including soil stabilisation in road and building construction, bleaching in the Kraft paper process, and use as a flocculant in water treatment. Calcium hydroxide (Ca(OH)2), a commodity chemical, is used in a wide range of industries, including food, environmental remediation, and construction. However, the current thermal process for producing Ca(OH)2 via limestone calcination is both energy and CO2-intensive.
