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Get to Know the Lime Water Formula and Find More About Calcium Hydroxide

Last updated date: 04th Mar 2024
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IVSAT 2024

An Introduction to Lime Water

Calcium hydroxide, also called slaked lime or lime water, is formed when water is added to calcium oxide or quicklime. This reaction is exothermic, therefore heat is also released along with calcium hydroxide. Since calcium oxide and water are combined together to form one by-product (calcium hydroxide), this reaction is also considered a combination reaction.

Slaked lime is also called by many other names, some of them are hydrated lime, pickling lime, caustic lime, etc. It is an amorphous white solid which is very stable and can withstand high temperatures.

Competitive Exams after 12th Science

What is Lime Water?

Lime water is a combination of calcium oxide, also called quicklime and water. It is the aqueous solution of calcium hydroxide. It forms slaked lime in the presence of water and the process is called slaking of lime. Calcium hydroxide is basic in nature; therefore it can be used to neutralise acidity in soil, etc. 

Few important things to know about calcium hydroxide:

Melting point- 852 K

Density - 2.211 grams/ cubic centimetre

Molecular weight - 74.093 grams per mole

Solubility at 20° - 1.73 g/L

Solubility at 0° - 1.89 g/L

Lime Water Chemical Formula

The chemical formula of lime water is  \[Ca{{(OH)}_{2}}\]

Equation for lime water: 

$CaO+{{H}_{2}}O\to Ca{{(OH)}_{2}}$

Preparation of Calcium Oxide

One of the ways to produce calcium oxide is by thermal decomposition of materials like seashells that contain calcium carbonate or limestone in a  lime kiln.

Carbon dioxide from calcium carbonate is removed using Le Chatelier's principle, leaving calcium carbonate as a compound. 

Colour of Calcium Oxide

Calcium oxide is usually of white or greyish white colour. It gives off a brilliant white colour when heated, near its melting point. This feature was used in the 19th century for stage lighting in limelights. It is odourless and appears to be in the form of hard lumps.

Properties of Calcium Oxide

Some facts about calcium oxide:

Density - 3.34 grams/ cubic centimetre

Molecular weight - 56.0774 grams per mole

Structure of Calcium Oxide

Calcium oxide contains a single calcium cation holding +2 charge and a single anion of oxygen holding -2 charge. Calcium oxide is an ionic bond that is formed due to electrostatic attraction between oppositely charged calcium and oxygen ions. Therefore,  calcium oxide features an ionic bond between calcium and oxygen.

Uses of Calcium Oxide

The following are some commonly known uses of calcium oxide.

  • Used in making porcelain and glass

  • Used in purifying sugar

  • In preparation of bleaching powder, calcium carbide and calcium cyanamide

  • In water softeners 

  • Also in mortars and cements

  • In agriculture it is also used for treating acidic soils. This process is called liming.

  • Due to its incandescence when heated it is used in Drummond lights or limelights also.

Important Questions

1. Why is carbon dioxide passed through lime water only for a short time?

Ans: When carbon dioxide is passed through lime water for a short time, milky white precipitate is formed but when reaction time increases precipitate dissolves leading to uncertain test results.

2. What can be observed when lime water is mixed with vinegar?

Ans: The reaction of lime water and vinegar is a neutralisation reaction. The products obtained during this reaction are salt and water.

3. What is calcination?

Ans:  It is a process to prepare burnt lime. In this process, reactants are thermally decomposed at high temperatures. But this temperature is kept below their respective melting points.


Calcium hydroxide is also called milk of lime. It is a mix of water and quicklime. Quicklime is formed when calcium carbonate is decomposed. It is also used in many industries. Some of its many uses include pH modifier due to its basicity, in the paper industry to convert wood into pulp, pickling cucumbers, production of plastics, etc. It is also used in production of ammonia, many plastics, pesticides, hair care products, ebonite, etc. It is further used in root canal procedures as slaked lime can be used to fill the cavities in teeth.  It is a white or colourless crystal powder. 

Practise Multiple Choice Questions

1. Calcium oxide reacts vigorously with water to form ____ ?

  1. Calcium Carbonate

  2. Calcium hydroxide

  3. Plaster of paris

  4. None of the above

Ans: Option 2 - Calcium hydroxide

2. Which of the following can describe reactions used for formation of slaked lime?

  1. Exothermic

  2. Combination reaction

  3. Both 1 & 2

  4. None of the above

Ans: Option 3 - Both 1 & 2

3. Calcium hydroxide is used to paint outer walls of buildings. Which of the following names describe this process?

  1. Whitewashing

  2. Calcimine

  3. Kalsomine

  4. Lime Paint

  1. A,C,D

  2. A,D

  3. C,D

  4. A,B,C,D

Ans: Option 4 - A,B,C,D

FAQs on Get to Know the Lime Water Formula and Find More About Calcium Hydroxide

1. What is an ionic bond?

It is a bond formed due to electrostatic attraction between oppositely charged ions. It is a bond that forms when the electrons are transferred from one atom to another. It is also called electrovalent bond. If an atom loses electrons it becomes positively charged also called cation and if it gains electrons it becomes negatively charged also called anion. Compounds formed by ionic bonds are called either ionic or electrostatic compounds. When a compound is formed electrons are arranged in such a manner that the overall charge on the compound becomes 0.

2. What is lime water used for?

Lime water is used in medicine, antacids and lotions and to absorb carbon dioxide. It is also used in the fermentation process to determine if carbon dioxide is released during the reaction since when lime water is in contact with carbon dioxide it turns milky white. Waste gases containing sulphur dioxide from industries are passed through lime water to separate sulphur dioxide from water and thus purify it. It further helps in unlocking proteins from cornmeal thus making it more nutritious for the person who eats it.

3. What are the important compounds of calcium?

Calcium oxide or quicklime that is formed by decomposition of calcium carbonate, calcium hydroxide or slaked lime that is formed by combination reaction between water and quick lime, calcium carbonate that is obtained from calcite, calcium sulphate or plaster of paris is manufactured by heating gypsum at 373-393 K , etc. are some of the many possible components formed with calcium. Calcium carbonate is a major constituent of limestone, shells, marble, coral chalk, etc. It is the most common calcium compound that can be found.