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

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.

Conclusion

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