[Chemistry Class Notes] on Calcium Hydroxide Pdf for Exam

Calcium hydroxide is commonly referred to as slaked lime and is described by the chemical formula Ca(OH)₂. It is also a white inorganic compound that has a powdery appearance in its solid-state. However, in its crystalline form, it has a colorless appearance.

 

The other names of this compound can be given as slack lime, hydrated lime, caustic lime, and pickling lime. In general, the calcium hydroxide is prepared by mixing calcium oxide (which is also called quicklime) and water.

Calcium Hydroxide Explained

Also, the chemical reaction between the calcium chloride and sodium hydroxide dissolved in water (aqueous CaCl₂) yields this compound. The structural representation of a Ca(OH)₂ molecule can be illustrated below.

 

The calcium hydroxide molecules are held together by ionic bonds between the two hydroxide ions (OH–) and calcium ions (Ca₂+). Unprotected exposure to this compound may prove dangerous to humans by leading to skin irritation and chemical burns. Exposure to the concentrated Ca(OH)₂ can lead to damage to the lungs and even blindness.

 

A few of the important properties of calcium hydroxide can be tabulated as follows:

Properties of Calcium Hydroxide

 

Physical Properties

Let us look at a few of the physical properties of calcium hydroxide as listed below:

• Ca(OH)₂ has a structure of hexagonal crystals.

• This compound is not very soluble in water. But, its solubility reduces with an increase in temperature. For suppose, its solubility at solubility is 1.73 g/L at 20℃ and at 0℃ is 1.89 g/L.

• This compound also tends to lose water and decompose at temperatures approaching its melting point.

• The solubility product (Ksp) of the calcium hydroxide can be given as 5.5 * 10-6.
  

Chemical Properties

Let us look at a few of the chemical properties of calcium hydroxide, as listed below.

• The calcium hydroxide is quite soluble in acids and glycerol, but it is slightly soluble only in water. It yields a solution that acts as a moderate base (called limewater) when it is dissolved in water to a saturation point.

• The lime water reacts with acids and forms salts.

• The saturated calcium hydroxide solution in water also reacts with and dissolves the metals such as aluminum.

• It also reacts with carbon dioxide and forms calcium carbonate (CaCO₃). In general, this reaction can be referred to as carbonation.
  

Why is Calcium Hydroxide less Soluble in Water?

Calcium hydroxide is also known as slaked lime in general is less soluble in water but, when its temperature is increased, it starts reaching its melting point and decomposes its material. The reason for this less solubility is due to a decrease in the lattice energy in hydroxide salts. The solution formed by the reaction of calcium hydroxide and water is called milk of lime. Unlike water, Calcium hydroxide is easily soluble in acids and glycerol hence, it is used as a pH corrector to reduce a solution’s acidity. 

Calcium hydroxide is added to water and sprayed on the soil to correct its pH level and recover the soil, it is also used in the construction of roadways and railways. But, adding it to the soil along with other fertilizers containing ammonium phosphate will reduce the nitrogen content of the soil. But, direct contact with Calcium hydroxide is harmful to humans and might cause loss of vision, so the US has banned adding Calcium hydroxide to the soil. Due to its pH value, Calcium hydroxide is also used as an antacid to treat burns and wounds caused by acids. Even the solution obtained from Calcium hydroxide and water also known as milk of lime is used as an antacid to treat burns and acid wounds.

Uses of Calcium Hydroxide

There are many different uses of calcium hydroxide, and a few of them are listed below. Let us have a look at those.

• Ca(OH)₂ can be used in the paper industry during the Kraft process, which converts wood into wood pulp.

• In the sewage treatment process, calcium hydroxide can be used as a flocculant or clarifying agent.

• It is an important compound in ammonia preparation.

• Generally, the cucumber pickling is done with the help of Ca(OH)₂.

• Also, this compound is used as a pH modifier because of its basicity.

• The production of various plastics involves the use of calcium hydroxide as a primary ingredient.

• In root canal procedures, this compound is used in filling the human teeth cavities.

• We can use it in pesticides, manufacturing of ebonite, and hair care products.

• Calcium hydroxide can be used in the leather industry to separate the fur or hair from the animal hide.

• Sugarcane and Sugar beets are processed via carbonation, which involves the use of Ca(OH)₂.
  

Native American Uses

In Spanish, the calcium hydroxide compound is known as cal. Maize cooked with cal (in a nixtamalization process) becomes hominy (nixtamal), which increases the bioavailability of niacin (vitamin B3) significantly, and also it is considered tastier and quite easier to digest.

 

Calcium hydroxide is usually chewed alongside chewing coca leaves to keep the alkaloid stimulants available chemically for absorption by the body. In the same way, the Native Americans chewed tobacco leaves traditionally with calcium hydroxide derived from the burnt mollusk shells to enhance its effects. Also, it has been used by a few indigenous American tribes as the main ingredient in yopo, which is a psychedelic snuff prepared from the beans of some species of Anadenanthera.