[Chemistry Class Notes] Hydrate Pdf for Exam

The crystalline chemical compound or the substances that contain a water molecule as a constituent of the compound is called hydrate. The water in these molecules combines chemically in a definite proportion. In hydrate compounds, the water molecules surround and interact with solute ions or molecules. The water molecules present in these compounds are called water of hydration. Some common example of hydrates are:

• Sodium hydrate.

• Copper hydrate.

• Calcium hydrate.

• Hydrates of carbon.

Hydration Process

The process of adding water to the compound is called hydration. This is the process in which water molecules surround and interact with solute ions or molecules. 

Water of Hydration

It is the form of water that is chemically combined with a compound to form a hydrated compound is called water of hydration. The water of hydration can be expelled from the compound by simple heating. The removal of water of hydration does not alter the composition of the substance essentially.

Such crystalline structures contain positive and negative ions. These ions are attached to the ionic bonds. The crystal lattice of these compounds contains water molecules. During the formation of the crystal lattice of these compounds, the water molecule gets traps in it. The presence of a water molecule in their crystal lattice is the main reason for the formation of such a special type of crystal structure. The mass of hydrated and dehydrated molecules will be different.

The mass of water of hydration molecule can find out by the formula:

Let the mass of the hydrated solid molecule = m₁

Let the mass of the dehydrated or anhydrous solid molecule = m₂

Mass of water molecule = m₁ – m₂

Hydrate Chemistry

When a polar compound is dissolved in water it gets split into two parts; cation and anion. The cation gets surrounded by the oxygen of the hydroxyl group (OH–) present in the water and the anion gets surrounded by the hydronium ion (H+) of the water molecule. 

Example: Copper Sulphate (CuSO4 . 5 H2O)

CuSO4 .5H2O → Cu+2 + SO4-2

In this compound, the copper ion and sulphate ions are surrounded by water molecules. Copper ions are surrounded by four water molecules and sulphate ions are surrounded by one water molecule. This difference is due to the nuclear charge. The nuclear charge on a copper ion is high (high nuclear charge) due to high charge density and the nuclear charge on sulphate ion is low (low nuclear charge) due to low charge density. The ion with more nuclear charge will combine more water molecules.

Different Types of a Hydrate

• Sodium hydrate.

• Calcium hydrate.

• Hydrates of carbon.

Sodium Hydrate-

Sodium hydrate is a hydrated form of the sodium ion. Its molecular formula is H₂ NaO⁺. The molecular weight is 41.00 g/mol. Its hydrogen bonding donor count is one. The formal charge of the sodium hydrate molecule is one. The structure of Sodium hydrate is given below:

Calcium Hydrate- 

Calcium hydrate is generally known as hydrated lime. Calcium hydrate is a hydrated form of calcium. The molecular weight is 92.11 g/mol. Its molecular formula is CaH4O3. The chemical name of calcium hydrate is calcium dihydroxide. Its hydrogen bond donor count is three. The formal charge of calcium hydrate is zero. The structure of calcium hydrate is given below:

Hydrates of Carbon- 

The hydrates of carbon are known as carbohydrates. These are the main source of energy. It is the first respiratory substrate in the human body. In hydrates of carbon, the ratio of hydrogen and oxygen is 2: 1. The generalized formula of the hydrates of carbon is Cx (H2O)y. Simple carbohydrates that are sweet are called sugar. Carbohydrates are the main source of energy in the body. In a normal man 55-65% of energy is available to him is in the form of carbohydrates present in his diet.

Types of Carbohydrates

Monosaccharides-

These are the simplest sugar that can not be further hydrolysed. In their generalised formula x is always equal to y. It means the number of carbon and oxygen atoms is the same. All monosaccharides occur in d and l form, except the dihydroxyacetone. Examples of monosaccharides are glucose, fructose, galactose, and mannose.

Oligosaccharides- 

Oligosaccharides are those carbohydrates that on hydrolysis yield 2 to 10 monosaccharide units. In this type of hydrate of carbon, monosaccharides are linked together by glycosidic linkage. Aldehyde or ketone group of one monosaccharide reacts with the alcoholic group of another monosaccharide to form a glycosidic bond. One molecule of water is eliminated during glycosidic bond formation.

Polysaccharides- 

These are composed of a large number of monosaccharides units. The suffix “an” is added in their names and they are known as glycans.

Did You Know?

The human brain is 95% water.

A person can lose a pint to a gallon of urine a day.

Do you know that water regulates the internal body temperature?

The water of hydration gives colour to the compound.

Moisture is a vaporized source of water.