Page 177 - ICSE Chemistry 8

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This is considered as a chemical change as sodium chloride dissociates into Na and Cl ions. That is why
water contains these ions and conducts electricity. It can also be called a chemical change because the
reactant sodium chloride here is diff erent from the products which are sodium ca on and chlorine anion.
On the contrary, dissolving a covalent compound like glucose does not result in a chemical change. When
glucose is dissolved in water, the molecules get dispersed throughout water but do not change their
chemical iden ty. There is no forma on of any new substance and the solu on retains the proper es of
both glucose and water.
Thus, any ionic compound which is soluble in water experiences a chemical change.

Water—A Universal Solvent

Water is called a universal solvent because it dissolves various solids, liquids and gases. It can dissolve
more substances than any other liquid. A substance that dissolves in water (or any other liquid) is called a
solute. Water or any other liquid in which a solute dissolves is called a solvent. The resul ng liquid mixture
formed is called a solu on.

Some of the solids that dissolve in water are salt, sugar and other inorganic and organic compounds. The
presence of certain minerals imparts taste to pure water. Liquids like alcohol, acids and bases also dissolve
quickly in water.
Some of the gases that dissolve in water are oxygen, carbon dioxide, ammonia, hydrogen chloride and
sulphur dioxide. Aerated drinks consist of carbon dioxide dissolved in water at high pressure.

Solubility

Solubility refers to the amount of solute that dissolves in a par cular solvent at a given temperature to
form a saturated solu on.

Solu on can be of three types on the basis of the amount of solute dissolved in the solvent: unsaturated
solu on, saturated solu on and supersaturated solu on.
Unsaturated Solution

A solu on in which some more solute can be dissolved at a specifi c temperature is called unsaturated
solu on.

Saturated Solution

A solu on in which no more solute can be dissolved at a specifi c temperature is called saturated solu on.
Supersaturated Solution

A solu on that contains more dissolved substance than could normally be dissolved at a specifi c
temperature is called supersaturated solu on.

Activity 8.5

Aim: To show that many substances can be dissolved in water
Materials required: Five glasses, water, sodium chloride, sodium carbonate, sodium bicarbonate, copper
sulphate, sugar

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