The key difference between calcium oxide and calcium hydroxide is that calcium oxide has a high density and it is more reactive, whereas calcium hydroxide has a low density and it is less reactive.
Calcium oxide and calcium hydroxide are both calcium compounds. Calcium oxide is also known as quicklime, while calcium hydroxide is known as hydrated lime.
What is Calcium Oxide?
Calcium oxide is an inorganic compound having the chemical formula CaO. It is also known as quicklime or burnt lime. We can describe this substance as a white, caustic, alkaline, and crystalline compound. It is odourless as well.
When considering the preparation of calcium oxide, this substance is usually manufactured by the thermal decomposition of limestone or seashells containing calcium carbonate in a lime kiln. In this preparation process, we need to heat the reactants to above 625 Celsius degree temperature. This heat treatment is called calcination. This process releases molecular carbon dioxide, which leaves quicklime. Since quicklime is not stable, it can spontaneously react with carbon dioxide when cooled, and after a sufficient time, it will completely convert back to calcium carbonate. Therefore, we need to slack it with water to set it as lime plaster or lime mortar.
The major use of calcium oxide is in the basic oxygen steelmaking process, where it can neutralize acidic oxides, silicone oxide, aluminum oxide, and ferric oxide, producing molten slag. Another important application of calcium oxide is using it in the production of aerated concrete blocks having varying densities.
What is Calcium Hydroxide?
Calcium hydroxide is an inorganic compound having the chemical formula Ca(OH)2. It is traditionally called slaked lime. It appears as colorless crystals or a white powder, and it can be produced by mixing calcium oxide with water. Some other names of calcium hydroxide include hydrated lime, caustic lime, builder’s lime, slaked lime, cal, and pickling lime. This compound has many applications, including food preparation, with the E number E526. The saturated solution of this compound is commonly named milk of lime.
The molar mass of calcium hydroxide is 74 g/mol. It appears as a white powder, and it is odorless. Moreover, the density of calcium hydroxide is 2.211 g/cm3. It has a melting point of 580 degrees Celsius and it has poor solubility in water. Moreover, it is soluble in glycerol and acid but insoluble in ethanol.
Calcium hydroxide has a polymeric structure similar to all metal hydroxides. This structure is identical to that of magnesium hydroxide. There are strong hydrogen bonds existing between the layers. Commercially, this compound is produced by treating lime with water.
What is the Difference Between Calcium Oxide and Calcium Hydroxide?
Calcium oxide and calcium hydroxide are inorganic compounds of calcium chemical elements. These are related to each other by chemical means. The key difference between calcium oxide and calcium hydroxide is that calcium oxide has a high density and it is more reactive whereas calcium hydroxide has a low density and it is less reactive.
The below infographic presents the differences between calcium oxide and calcium hydroxide in tabular form for side-by-side comparison.
Summary – Calcium Oxide vs Calcium Hydroxide
Calcium oxide is an inorganic compound having the chemical formula CaO while Calcium hydroxide is an inorganic compound having the chemical formula Ca(OH)2. The key difference between calcium oxide and calcium hydroxide is that calcium oxide has a high density and it is more reactive, whereas calcium hydroxide has a low density and it is less reactive.
1. “Calcium Hydroxide.” VEDANTU, 27 Apr. 2022.
1. “Calcium oxide powder” By Leiem – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Calcium hydroxide” – Picture taken by w:User:Walkerma in June 2005. – Own work (Public Domain) via Commons Wikimedia