What is the Difference Between Quick Lime and Hydrated Lime

The main difference between quick lime and hydrated lime is that quick lime is typically more reactive than hydrated lime.

Quicklime and hydrated lime are distinct chemical compounds with different properties and uses. Quick lime is a compound composed of a single calcium atom and an oxygen atom, whereas hydrated lime is a compound composed of calcium, oxygen, and two hydrogen atoms.

Key Areas Covered

1. What is Quick Lime  
     – Definition, Properties, Reactivity  
2. What is Hydrated Lime
     – Definition, Properties, Reactivity
3. Similarities Between Quick Lime and Hydrated Lime
     – Outline of Common Features
4. Difference Between Quick Lime and Hydrated Lime
     – Comparison of Key Differences

Key Terms

Calcium Hydroxide, Ca(OH)₂, Calcium Oxide, CaO, Hydrated Lime, Limestone, Quick Lime

What is Quick Lime

Quicklime, scientifically known as calcium oxide (CaO), is a powerful compound composed of a single calcium atom and an oxygen atom. This compound results from the thermal decomposition of limestone (calcium carbonate) through a process called calcination. The high temperature of the kiln breaks the bond between the calcium and carbon atoms in limestone, releasing carbon dioxide gas and leaving behind quicklime.

The production of quicklime involves subjecting limestone to temperatures ranging from 900 to 1300 degrees Celsius in a kiln. This process is a chemical transformation that has been utilized for centuries. The result is a highly reactive substance that is alkaline in nature.

Stated below are some applications of quick lime.

• In the steel industry, quicklime acts as a flux, aiding in the removal of impurities from iron during the smelting process.
• Due to its alkaline nature, quicklime is employed for water treatment. It adjusts pH levels, softens water, and precipitates impurities in wastewater treatment.
• Quicklime is helpful in construction to produce mortar and plaster through the process of hydration. It enhances the strength and durability of these materials.

What is Hydrated Lime

Hydrated lime, known as calcium hydroxide, has the chemical formula of Ca(OH)₂. At its core, hydrated lime is the result of a controlled reaction between quicklime (calcium oxide, CaO) and water. This process, known as slaking, involves adding water to quicklime in a precise manner, leading to a chemical transformation. The outcome is a compound composed of one calcium atom, two oxygen atoms, and two hydrogen atoms, expressed as Ca(OH)₂. This chemical composition underpins the myriad properties and applications of hydrated lime.

The production of hydrated lime involves a careful balance of reactivity and control. Quicklime is mixed with an appropriate amount of water to initiate the slaking reaction. The reaction is exothermic, meaning it releases heat. This exothermic reaction not only results in the formation of hydrated lime but also underscores the precision required in managing the reaction to prevent overheating.

Hydrated lime takes center stage as an essential ingredient in mortar and plaster. When mixed with water and aggregates, hydrated lime enhances the cohesion, workability, and durability of these materials. Its presence contributes to the formation of strong bonds between particles, resulting in structures that stand the test of time.

In agriculture, hydrated lime finds its purpose in soil stabilization and pH adjustment. By modifying soil pH, hydrated lime creates conditions conducive to optimal plant growth. It can also mitigate soil acidity and improve soil structure, promoting healthier crops. It also helps to treat acidic mine drainage, neutralize contaminants, and improve the quality of soil and water in contaminated areas.

Similarities Between Quick Lime and Hydrated Lime

• Quicklime and hydrated lime are alkaline substances.
• Both quicklime and hydrated lime find applications in the construction industry.
• Both compounds contain calcium, oxygen, and hydrogen atoms.

Difference Between Quick Lime and Hydrated Lime

Definition

Quick lime is calcium oxide and has the chemical formula CaO, whereas hydrated lime is calcium hydroxide and has the chemical formula of Ca(OH)_2.

Composition

Hydrated lime is composed of calcium, oxygen, and two hydrogen atoms, while quick lime is composed of a single calcium atom and one oxygen atom.

Production

Hydrated lime is produced by adding controlled amounts of water to quick lime, while quick lime is produced by calcinating limestone (calcium carbonate) at high temperatures.

Physical Form

Quick lime is typically sold in the form of large, white or grayish lumps or granules. It is solid and caustic, with a high pH value. Hydrated lime is a fine, white powder. It is less caustic than quicklime and has a lower pH value because it contains water.

Reactivity

Moreover, quick lime is highly reactive with water, and it generates significant heat during the hydration process. Hydrated lime is less reactive with water than quick lime.

Conclusion

Quick lime and hydrated lime are distinct chemical compounds with different properties and uses. Quick lime is the result of heating limestone and is highly reactive, while hydrated lime is produced by adding water to quick lime and is less reactive, making it suitable for a wider range of applications. Thus, this is the main difference between quick lime and hydrated lime. 

Reference:

1. “Calcium hydroxide | Definition, Formula, Uses, Properties, & Facts.” Encyclopedia Britannica.
2. “Quicklime | Formula, Uses, & Definition.” Encyclopedia Britannica.

Image Courtesy:

1. “The lime cycle” By Peter Bell – (CC BY-SA 3.0) via Commons Wikimedia
2. “Calcium hydroxide” By Picture taken by w:User: Walkerma in June 2005. – Own work (Public Domain) via Commons