Slaked lime is the common name for the chemical compound calcium hydroxide(Ca(OH)₂). Calcium hydroxide is also known by other common names: caustic lime, hydrated lime, slack lime, and pickling lime. The saturated solution for slaked lime is also referred to as limewater.
This compound exists in nature as a white substance in the form of a powder. However, the compound can also exist as colorless crystals at Standard known Temperature and Pressure.
As we know, Slaked lime has the chemical formula Ca(OH)₂, i.e., calcium hydroxide. The preparation methods involve chemical reactions between calcium oxide and water. Calcium oxide, also otherwise known as quicklime, reacts with water. During this reaction, a small amount of quicklime is dissolved into water, thus forming slaked lime. The chemical reaction for the following can be represented as:-
Cao + H2O 🡪 Ca(OH)2
While some portion of the quicklime is involved in the formation of slaked lime, the remaining portion is present as suspension. This suspension is also popularly known as lime milk.
Another method of preparation of slaked lime is through the chemical reaction between calcium chloride and sodium hydroxide. Calcium chloride and sodium hydroxide can be represented with the help of the chemical formula CaCl2 and NaOH, respectively. When aqueous solutions of calcium chloride and sodium hydroxide are mixed, the chemical reaction results in calcium hydroxide, i.e., slaked lime and salt, i.e., NaCl. The chemical reaction is represented as follows:-
CaCl2 + 2NaOH 🡪 Ca(OH)2 + 2NaCl
Some of the properties of Slaked lime are listed as follows:-
Slaked lime is observed to undergo a decomposition reaction and lose water when the temperature is as close to 853 K. It is to be noted that there can be side effects caused by slaked lime or slaked lime solutions. With higher ph values, the solubility of slaked lime decreases drastically.
It is also observed that at 70 ° C, calcium hydroxide, aka slaked lime has its solubility at around half of its value at that observed in 25 ° C. The explanation for this is that the dissolution reaction of slaked lime in water is exothermic. It also adheres to Le Chatelier’s principle. Thus, a drop in temperature favors the removal of heat emitted through the dissolution process and raises the equilibrium constant of the calcium hydroxide dissolution, thereby increasing its solubility at low temperatures. This dependence of solubility on temperature is commonly referred to as solubility “retrograde.”
Some of the common reactions of slaked lime with other chemicals are listed as follows:-
The applications of slaked lime are listed as follows:-
1. For whitewashing – Slaked lime is used in whitewashing. It reacts with carbon dioxide slowly and forms a layer of calcium carbonate on the wall, giving the wall shine.
2. For the manufacturing of sugar – Slaked lime is used in manufacturing sugar from sugar cane. It makes sugarcane juice alkaline and precipitates its impurities.
3. It is used in sewage treatment. It is used as a flocculant in water.
4. It is used in the paper industry.
Other uses include processing and making pickles, water for various beverages, and the cellulose hull of maize kernels. It is also used as a digestive aid, making papadum, etc.