Who doesn’t like to come into the limelight? Make a hilarious song or just be yourself during any vacation to some offbeat area- If you reel it, you are under the limelight! Fame is the limelight that everyone loves to come under, isn’t it? But hey! Are you really aware of what is the origin of this ‘limelight’?
What if I say, ‘limelight’ is actually ‘calcium oxide’! Sounds incredible? Indeed, it is incredible. Once upon a time, before the advent of electricity, all the theatres, music halls and stage productions used to use a source of calcium oxide, which when heated up to its melting point, would give off a very bright light, known as the ‘limelight’. This intriguing limelight effect was first discovered in the 1820s by Goldsworthy Gurney.
A strong illumination is created when an oxyhydrogen flame is directed at a cylinder of CaO which can be heated to 2,572 °C before melting. Isn’t it amazing? So why wait? Let’s put some limelight into the “limelight’’ and dive straight into exploring more about this historically glorious chemical and understanding its chemistry.
TABLE OF CONTENTS
Calcium oxide with the molecular formula CaO is referred to as lime, quicklime, baked lime and also burnt lime. It is a white, alkaline and crystalline chemical compound that is widely used in industries and pharmaceutical companies for its physical and chemical properties.
Calcium oxide is used for making various building products such as cement which is called free lime. It is an alkaline substance which has been used by human beings as far back as the medieval age and thus calcium oxide was dubbed as the oldest chemical used by human beings.
The history of calcium oxide goes long back to the ages of ancient times. The Roman writer Cato the Elder (234 - 149 BC) mentioned a method for making calcium oxide in 184 BC.
By the early 15th century, multiple European citizens were using calcium oxide (referred to as lime) in the construction of buildings. Scottish chemist Joseph Black (1728–1799) performed several early scientific studies of calcium oxide. He found that when the compound is exposed to air, it combines with carbon dioxide to produce calcium carbonate.
Calcium oxide (CaO) molecules contain one calcium cation (which holds a charge of +2) and one oxygen anion (which holds a charge of -2). calcium oxide is an ionic compound featuring an ionic bond between calcium and oxygen. The lewis structure of calcium oxide is illustrated below.
In the solid crystalline structure of CaO , all the O2- ions occupy corners and face centres in the FCC arrangement and Ca2+ ions occupy all the octahedral voids.
Calcium oxide (CaO) is usually made by the phenomenon of thermal decomposition which occurs with materials such as seashells or limestone. These materials are rich in calcium carbonate and are converted into calcium oxide using a lime kiln or a rotary kiln. This is accomplished by heating the material to above 1070-1200K.
This is a process called calcination or lime-burning. The heating is applied in order to liberate a molecule of carbon dioxide, leaving only quicklime as the product.
Calcium oxide when absorbs CO2 on exposure to the atmosphere produces calcium carbonate.
Q1. Calcium oxide is:
A. Ionic Solid
B. Covalent Solid
C. Covalent Liquid
D. None of the above
Solution: Calcium oxide is made of calcium (Ca2+) and (Cl-) ions. So they form ionic bonds and hence it is solid in nature. So Option A is the correct answer.
Q2. The formula of Quicklime is:
Solution: Quicklime is the common name for calcium oxide which is also called lime. Calcium hydroxide is called slaked lime in common terms. .
Q3. Why is calcium oxide used as refractory material?
Answer: The melting point of calcium oxide (CaO) is 2572 °C. Due to a high melting point, it is used as a refractory material, as it does not melt easily on heating and is also hence used to produce limelight.
Q4. What is the product obtained from the decomposition of calcium carbonate?
B. Slaked lime
C. Calcium Oxide
D. No reaction
Solution: Calcium carbonate on decomposition at a temperature of around 1200 K produces calcium oxide and carbon dioxide.
Question 1. What is limewater? Is it drinkable?
Answer: Limewater is obtained when calcium oxide reacts with water and forms a calcium hydroxide solution. Yes, it is drinkable. In fact it aids digestion. It mimics the activity of hydrochloric acid in the stomach and helps in preventing indigestion, stomach upsets etc.
Question 2. Is Calcium oxide soluble in water?
Answer: Yes, it is soluble in water and it readily absorbs moisture from the atmosphere. It is also able to absorb carbon dioxide from the atmosphere and forms calcium carbonate.
Question 3. What are the health-related risks related to calcium oxide?
Answer: Quicklime can cause severe irritation, especially when inhaled or if it comes in contact with wet skin or eyes.
Question 4. Give an example of unusual usage of quicklime?
Answer: They are used to make ‘’Bitan egg’’ or “Century egg’’, which is a Chinese culinary item, which is basically preserved duck, quail, and chicken eggs aged for weeks or even months by using a mixture of clay, ash, salt, quicklime and rice hulls. The yolk turns black and the shell turns brownish and jelly-like.
They are also famously known as hundred-year eggs, thousand-year eggs.
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