Solutes-Solvents-Solutions

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We come across many kinds of solutes, solvents and solutions in our day-to-day life. For e.g., we use solutes, such as salt and sugar, in beverages and other foods. A bottled soft drink usually contains sugar, carbon dioxide and other solutes, dissolved in a solvent i.e., water. We often use the solution of salt in hot water to ease a sore throat by gargling.

Solute

is a substance that can dissolve in a solvent, to form a solution.

Examples: Salt, sugar, etc.

Solvent

is a substance that can dissolve a solute, to form a solution.

Examples: Water, alcohol, kerosene, petrol, etc.

Solution

is a homogeneous mixture of a solute dissolved in a solvent.

Examples: Salt and water, sugar and water, iodine and alcohol.

It should be remembered that:

1. A Solution is a homogeneous mixture of two or more substances. These substances can be in any of the three physical states.

2. If both the constituents in a mixture are in the same state, then, the one that is lesser in quantity is considered to be the solute, and the other, the solvent. For e.g., alcohol and water dissolve in each other. If a small quantity of alcohol is added to water, water is the solvent, and alcohol the solute. But if a small quantity of water is added to a beaker of alcohol, then alcohol is the solvent and water is the solute.

Remember:

Alloy

is a solution of two or more metals fused together and then frozen. An alloy may also contain small quantities of non-metals. Example: Carbon in steel.

Air

is a solution of oxygen, nitrogen and carbon dioxide.

Tincture

is a solution, in which the solvent is alcohol. Example: Tincture of iodine.

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Table 6.2 - Some Water Soluble Solids

Anions	Soluble combination of Cations	Insoluble ones
Carbonates	Potassium, Sodium and Ammonium	All others
Nitrates	All nitrates	None
Chlorides	Most	Lead (II) and Silver and Mercury (I)
Sulphates	Most	Calcium, Lead, Silver, Mercury (II), Barium and Strontium.

 

Remember

All salts of sodium, potassium and ammonium (whether these are carbonates, nitrates, chlorides or sulphates) are soluble in water.

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Table 6.3 - Some Common Solutes and their Solvents

Solute	Solvent
Chlorophyll	Acetone, Alcohol
Fats	Oils, Benzene, Carbon disulphide
Crease	Kerosene, Petrol, Benzene, Carbon disulphide
Iodine	Alcohol, Chloroform
Naphthalene	Acetone, Benzene, Chloroform, Carbon disulphide
Phosphorus	Benzene, Carbon disulphide
Sulphur	Carbon disulphide, Carbon tetrachloride, Xylene
Wax	Benzene, Turpentine

 

Kinds of Solutions

As we have mentioned earlier, the solvent can be solid, liquid or a gas. At the same time, the solute can also be a solid, liquid or a gas. The following table (Table 6.4) gives examples of different types of solutions. The first column shows the solute and the second, third and fourth columns show the type of solvent that has produced the solution, in the different states.

Table 6.4 - Examples of different types of solutions

Solute/Solvent	Solid	Liquid	Gas
Solid	Alloys	Salt in water	Smoke, Clouds
Liquid	Mercury in copper	Alcohol in water	Mist, Fog
Gas	Hydrogen in palladium	Air in water	Air

 

 

 

 

 

Types of Solutions

a) Saturated solution

A solution that cannot dissolve any more of a solute at a given temperature, is called a "saturated solution".

Take some water in a beaker at room temperature. Add some common salt and stir. The salt dissolves. Keep on adding more of the salt and go on stirring. The added salt goes on dissolving. When a solution can dissolve some more of the solute it is called "unsaturated solution".

Now, if you go on adding salt, a time will come when it will not be possible to dissolve any more of the salt, even with repeated and vigorous stirring. The solution has become saturated with salt at that temperature. Such a solution is called a "saturated solution".

Now, if you warm the saturated solution slightly and add salt, you will notice that some more salt will dissolve. Thus, if the temperature of the saturated solution is raised, the said solution becomes unsaturated at the higher temperature.

b) Dilute solution

It is an unsaturated solution that contains comparatively small quantity of the solute, compared to what it can dissolve at that temperature.

c) Concentrated solution

It is a solution that contains comparatively a higher proportion of the solute, compared to what it can dissolve at that temperature.

Characteristics of a Solution

1. Appearance

Clear and transparent, especially in dilute form.

2. Sub-division of particles

The solute breaks up into tiny particles, which could even be of ionic or molecular size. Solute particles become too small as compared to the pores of a filter paper and they pass through filter paper along with solvent particles. This is why it is not possible to separate the solute and solvent from a solution by filtration.

3. Sedimentation of particles does not occur in a solution

The particles of the solute, in the solution will not settle down. A true solution can be preserved for any length of time without any sedimentation taking place. Seas and oceans have contained sodium chloride since millions of years, but crystals of salt cannot be seen on the sea-bed or ocean-bed.

4. Homogeneity

Solutions are homogeneous in character. If you add a pinch of salt to a glass of water, the particles of salt spread out evenly throughout the water.

5. No definite composition

A solution is a mixture. Mixtures of the same substances can be mixed in varying proportions. Hence, solutions do not have any definite composition.