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Calcium Oxide is an alkaline substance found in the form of crystalline or powdery solid. The formula for the compound is CaO. CaO is present in either white or off-grey in its natural state.
- Calcium Oxide is found in a slightly yellowish or brownish colour due to the presence of impurities and dirt.
- It is also known as quicklime or, burnt lime or lime.
- Quicklime is also among the oldest chemical substances found in human history.
- The substance had been in use since the medieval age.
- It is an alkaline, crystalline compound at room temperature.
- Calcium oxide is prepared by thermal decomposition of materials like limestone and sea shells.
- The ionic structure of the compound contains Ca2+ and O2-.
- There are various uses of substances throughout the world, be it in the medical field, lab use, construction material, etc.
Key Terms: Calcium Oxide, Calcium Carbonate, Limestone, Quicklime, Magnesium, Oxygen, Calcium, Alkaline, Thermal Decomposition, Calcination, Melting Point, Boiling Point, Solution, Alcohol, Entropy
What is Calcium Oxide?
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Calcium Oxide is a chemical compound widely known by its other names, such as quicklime, lime, fluxing lime, or unslaked lime. It is formed by the elements calcium and oxygen with the chemical formula CaO.
- Calcium Oxide is a metallic oxide generally found in the solid state at room temperature.
- In CaO, calcium contains inorganic materials, with elements like magnesium, aluminium, silicon, and iron.
- Besides the above inorganic compounds, other inorganic compounds include oxides and hydroxides of calcium.
- Calcium Oxide has a molecular weight of 56.08 g/ mol.
- It has a melting point of 2,572 degrees Celsius and a boiling point of 28500 degrees.
- The important reaction carried out by calcium oxide is as follows:
CaCO3(s) → CaO(s) + CO2(g)
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| Chapter Related Concepts | ||
|---|---|---|
| Calcium Chloride | Calcium Sulphate | Barium Oxide |
| Nitrogen | Binary Compound | Ferrous Sulphate |
Structure of Calcium Oxide
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The structure of calcium oxide molecule consists of one oxygen anion and one calcium cation. The charge of calcium cation is +2 and charge of oxygen anion is -2 anion.
- An ionic bond is formed between calcium and oxygen.
- The oxygen anion will occupy corner and face centre position.
- Cation of calcium will occupy octahedral voids.
- The structure of calcium oxide are as follows:
Calcium Oxide
Preparation of Calcium Oxide
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The preparation of calcium oxide or quicklime contains a few simple steps. Its preparation dates back to the stone age as it can be easily prepared from the readily available limestones in nature. The steps of preparation for CaO are as follows:
Lime Water Formula
Calcium oxide can be prepared using limewater. The limewater structural formula is given as Ca(OH)2. The chemical name for the compound is calcium hydroxide. It is a strong exothermic reaction that results in the formation of steam.
- Calcium Oxide is formed when water is added to calcium hydroxide.
- The process is also known as slaking lime.
- It can be represented with an equation which is as follows:
CaO + H2O → Ca(OH)2
Calcination
Calcination is a process of thermally decomposing the reactants of the calcium oxide at high temperatures (1070°C - 1270°C), i.e., below its melting point. It can be produced through the process of thermal decomposition of limestones or seashells that are easily found in nature.
- Limestones or Seashells contain calcium carbonate (CaCO3), which is further processed into burnt lime.
- The products formed by calcination are burnt lime and carbon dioxide.
- To represent it symbolically, the chemical formula for Calcium Oxide is:
CaCO3 → CaO + CO2
Physical Properties of Calcium Oxide
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The physical properties of calcium oxide are as follows:
- Calcium Oxide is a shapeless white amorphous liquid.
- It has high melting and boiling point.
- It readily reacts with water to form calcium hydroxide, also called slake lime.
- CaO is a very stable compound that is hard to decompose.
- The compound is basic in nature.
- It is soluble in acid and forms salts.
- The standard molar entropy of calcium oxide is 40 joule/ mole kelvin.
- Calcium oxide is insoluble in alcohol.
| Category | Data |
|---|---|
| Calcium Oxide | CaO |
| Molar Mass | 56.0774 g/mol |
| Density | 3.34 g/cm³ |
| Boiling Point | 2,850 °C |
| Solubility | Soluble in water & glycerol |
| Melting Point | 2,572 °C |
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| Class10 Chemistry Related Concepts | ||
|---|---|---|
| Oxides of Nitrogen | Milk Of Magnesia | Hydroxide |
| Iron Oxide | Nitrous Oxide | Silver Oxide |
Chemical Properties of Calcium Oxide
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The chemical properties of calcium oxide are as follows:
- Calcium Oxide is used for the neutralization of acids forming water and calcium salts as the end products.
CaO + 2HCl → CaCl2 + H2O
- Calcium hypochlorite can be formed by the reaction of calcium oxide with chlorine gas. The formula for calcium hypochlorite is [Ca(ClO)2].
CaO + Cl2 → Ca(ClO)2
- Calcium oxide, when heated with carbon dioxide, will result in the formation of carbon monoxide.
- It acts as a reducing agent that is a strong alkaline compound.
- CaO will exhibit the properties of electrolysis of metals in the presence of water or in the case of molten form.
Calcium Oxide
Uses Calcium Oxide
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Calcium Oxide has number of uses in various fields. Some of its most common uses are given below:
- Calcium Oxide is often used as a water-softening agent.
- The compound is also used in the recovery of ammonia.
- It is extensively used in laboratories as a reagent for the absorption of gases and precipitation.
- Quicklime is used on large scales for various medicinal purposes, such as animal food, insecticides, etc.
- CaO is extensively used in the production of soap, refractories, varnish, etc.
- It is also used as a reagent for producing cement, lime bricks, steel, etc.
- CaO is the cheapest alkali that is also used in the manufacturing of caustic soda.
- It is used as a preservative for poultry feed.
- Calcium Oxide is used to improve soil quality.
- It is widely used as a filler in paper products.
Side Effects Of Calcium Oxide
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Calcium Oxide is a very active compound that can be harmful to your health in many ways. The various health risks one might suffer from due to Calcium oxide are as follows:
- Calcium oxide, if inhaled, might cause health problems like sneezing, cough, and other breathing problems.
- It can cause extensive irritation if inhaled or if it comes into contact with wet skin.
- Other health effects of CaO include vomiting, abdominal pain and nausea burns.
Things to Remember
- Calcium Oxide, on heating near its melting point, gives off a laminating white light.
- Heated Lime was also used to illuminate the stage productions before the discovery of the electric bulb.
- CaO is also used in the lake waters to neutralize the water that the acid rain had acidified.
- It is used as a food additive in most food items to maintain their acidity and provide bulk to the products.
- In the early days, quicklime was also used to bury diseased animals and humans.
- It is believed to fasten the decomposition process of the soft tissues, which was very common during those days.
Sample Questions
Ques. 2.8g of calcium oxide (CaO) prepared by heating limestone was found to contain 0.8g of oxygen. When 1g of oxygen was treated with calcium, 3.5g of calcium oxide was obtained. Show that the results demonstrate the law of definite proportions? (4 marks)
Ans. As per the given data, we have:
Case I:
2.8g of CaO contains 0.8g of oxygen.
We know that Mass of CaO is = 2.8 - 0.8 = 2g
Therefore, ratio of mass of calcium to oxygen is = 2/ 0.8 = 2.5
Case II:
3.5g of CaO contains 1g of oxygen.
Hence, mass of Calcium in CaO is = 3.5 - 1 = 2.5g
Ratio of mass of calcium to oxygen is = 2.5/1 = 2.5
Hence, with the result from the given data and, as per the definition of the laws of proportion, we can conclude that the above condition satisfies the laws of proportion.
Ques: How is calcium effective to your health? (1 marks)
Ans. Calcium is most important for the bones. It makes your bones more brittle and stronger. Besides, it also helps a lot in controlling hypertension. Calcium can be consumed from your daily diet or externally from calcium capsules.
Ques. Solid calcium oxide was taken in a container and water was added slowly into it. Write the name and the chemical reaction for it? (2 marks)
Ans: The chemical formula for the above reaction is:
CaO (s) + H2O (l) → Ca (OH)2 + heat.
The compound produced due to the above reaction is calcium hydroxide and some amount of heat has been released.
Ques. Solve following question (A) Is calcium oxide toxic (B) Where is Calcium Oxide used? (2 marks)
Ans. (A) Yes, Calcium Oxide is shortly toxic as it can irritate the eyes and skin if someone breathes it. It can also burn or irritate the lungs. It can cause cough and shortness of breath also.
(B) Calcium Oxide is also used in the recovery of ammonia, and in laboratories. It is used for various medicinal purposes. It is also used as a reagent for producing cement, lime bricks, and steel.
Ques. 3.8g of calcium oxide (CaO) prepared by heating limestone was found to contain 1.8g of oxygen. When 1g of oxygen was treated with calcium, 3.5g of calcium oxide was obtained. Show that the results demonstrate the law of definite proportions? (4 marks)
Ans. As per the given data, we have:
Case I:
2.8g of CaO contains 0.8g of oxygen.
We know that Mass of CaO is = 3.8 - 1.8 = 2g
Therefore, ratio of mass of calcium to oxygen is = 2/ 1.8 = 1.11
Case II:
3.5g of CaO contains 1g of oxygen.
Hence, mass of Calcium in CaO is = 3.5 - 1 = 2.5g
Ratio of mass of calcium to oxygen is = 2.5/1 = 2.5
Hence, with the result from the given data and, as per the definition of the laws of proportion, we can conclude that the above condition satisfies the laws of proportion.
Ques. How calcium oxide can be used to improve the quality of air and water? (2 marks)
Ans. Calcium Oxide is responsible for capturing the particles of sulphur dioxide. It helps in the reduction of acid rain and air pollution, which in turn will improve the quality of air. The compound reduces the water's hardness and removes the various metal compounds present in the water. It will improve the quality of water, thus making it safer for consumption.
Ques. What are the uses of calcium oxide? (3 marks)
Ans. The various uses of calcium oxide are as follows:
- Calcium oxide is used in the preparation of cement for buildings.
- It is used in sprays or slurries to sulphur dioxide from exhaust steam.
- During earlier times calcium oxide was used in the war to defeat the enemy.
- The compound is used in paper industry to regenerate sodium hydroxide.
- Calcium Oxide is used in industrial plasters and mortars.
Ques. What is the difference between the calcium oxide and calcium hydroxide? (4 marks)
Ans. The difference between the calcium oxide and calcium hydroxide are as follows:
| Calcium Oxide | Calcium Hydroxide |
|---|---|
| Calcium Oxide is also known as quick lime | Calcium Hydroxide is also known as slaked lime. |
| Its chemical formula is CaO. | Its chemical formula is Ca(OH)2. |
| Calcium Oxide is a white, alkaline crystal. | Calcium Hydroxide is a colouless crystal. |
| It is used for medicinal purpose and insecticides. | It is used in food industry. |
Ques. Calculate the molecular mass of Calcium Oxide? (2 marks)
Ans. The molecular mass of calcium oxide is calculated as follows:
- The formula for calcium chloride is CaO.
- As the molecular mass of Calcium is 40.08 grams
- Molecular mass of Oxygen is 16 grams.
- So the molecular mass of Calcium Oxide will be: 40.08+16
The molecular mass of calcium oxide is 56.08 gram per mole.
Ques. What are the health benefits of calcium on human body? (3 marks)
Ans. The health benefits of calcium on human body are as follows:
- Calcium is used for keeping our bones stronger.
- It is used for the maintenance of oral health.
- The compound is useful for growth, development, and maintenance of the body.
- Calcium is responsible for muscle contraction and improves cholesterol functioning.
Ques. What is carbonation? (2 marks)
Ans. Carbonation is defined as a process where calcium oxide absorb carbon dioxide from the atmosphere. The absorb carbon dioxide and calcium oxide is converted into calcium carbonate. It is used to affect the functioning of mortar or concrete containing calcium oxide.
CaO(s) + CO2(g) → CaCO3(s)
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