StopLearnStopLearnDefinition of Terms
Solute
This is a substance that dissolves in a solvent to form a solution. It can be solid, liquid or gas. Examples include common salt, sugar, copper (II) tetraoxosulphate (VI) etc.
Solvent
This is a substance that dissolves a solute to form a solution. It can be liquid or gas. Examples are water, ethanol, benzene etc.
Solution
This is a mixture of solute and solvent, i.e,
Solute + Solvent = Solution
It can be homogeneous with a uniform composition, e.g, an unsaturated solution of a sodium chloride, or heterogeneous with non-uniform composition like an unsaturated solution of the same salt.
Solution is defined as a homogeneous mixture of two or more chemical substances. The state of matter of a solution may be solid, liquid or gaseous.
For example, common salt in water (liquid solution), air (gaseous solution), alloys (solid solution), etc.
The components of a solution may be classified as:
| Basis for Comparison | Solute | Solvent |
|---|---|---|
| Meaning | The substance that gets dissolved in the solvent in a solution is called as the solute; the solute is present in the lesser amount than the solvent. | The substance that dissolves the solute in a solution is called as the solvent; the solvent is present in the higher amount than the solvent. |
| Boiling point | The boiling point is higher than solvent. | It is lower than that of solute. |
| Physical state | Found in solid, liquid or gaseous state. | Mainly in the liquid state, but can be gaseous as well. |
| Dependability | Solubility depends on the properties of the solute. | Solubility depends on the properties of the solvent |
Thus, an intimate mixture of solute and solvent is called a solution.
Solutions that contain water as the solvent are called aqueous solutions.
For example, sugar in water, carbon dioxide in water, etc.
Solutions that contain a solvent other than water are called non-aqueous solutions. Ether, benzene, petrol, carbon tetrachloride etc., are some common solvents.
For example, sulphur in carbon disulphide, naphthalene in benzene, etc.
Between two solutions, the solute quantity may be relatively more or less. The solution that has a greater proportion of solute is said to be more concentrated than the the other that has a lesser proportion. If the proportion of solute is less, the solution is said to be dilute.
Saturated Solution
A saturated solution is one that holds as much solute as it can dissolve in the presence of undissolved solute particles at a given temperature. In a saturated solution, the dissolved and undissolved solutes are in equilibrium at a given temperature.
Unsaturated Solution
An unsaturated solution is one that can still dissolve more solutes at a given temperature until it becomes saturated.
For instance, the solubility limit of sodium chloride is 36g dm^-3, which means that as long as the mass of sodium chloride in 1dm^3 of its solution is below 36g, the solution will remain unsaturated. However, immediately the mass is 36g and above, the solution will be considered to be saturated because any mass in excess of 36g will be precipitated out of solution as undissolved particles. This implies that if the mass of sodium chloride in the solution is 37g; 1g which is the excess will be precipitated out as undissolved particles.
A solution which contains more of the solute than it can normally hold at a given temperature is said to be supersaturated. The supersaturated solution is unstable at a given temperature and the solute particles can crystallize out of the solution at the slightest touch or addition of a dry crystal of the solute. At times, dust particles can cause the crystallization of the solute particles. Also, merely scratching the inside of the glass vessel holding the solution with a glass rod or spatula can cause the solute particles to crystallize out. This is known as seeding, and is employed in crystallization as a separation technique. Solution and solubility
Solubility is defined as the number of grams of a solute that dissolves in 100g of a solvent to form a saturated solution at a given temperature and pressure.
Solubility is the maximum weight of a solute that can be dissolved in 100g of a solvent at a given temperature and pressure.
Increase in temperature increases the solubility.
For example, it is easier to dissolve sugar in hot milk than in cold milk.
Smaller the size of the particles greater is the solubility.
For example, it is easier to dissolve powdered sugar than granules of sugar.
Mechanical stirring increases solubility.
For example, sugar dissolves faster on stirring with a spoon.
Increase in temperature, decreases the solubility of a solute. On heating, the gases dissolved in milk escape making the milk bubble and boil over.
An increase in pressure increases the solubility of a gas.
For example, aerated water bottles contain carbon dioxide gas under pressure.
Pressure directly influences the solubility of gases. Higher the pressure, higher is the solubility: lower the pressure, lower is the solubility. For instance, the solubility of carbon dioxide in water, under normal atmospheric pressure is very low. But when subjected to higher pressure it dissolves to a great extent, as in the case of aerated waters.
Remember
From our day-to-day experience, we come to know that a solid can dissolve faster if:
So the fastest way to dissolve a solid in a liquid is to grind the solid into very tiny particles, stir the mixture, and use a hot solvent. Dissolving Bournvita in a hot cup of milk is a good example!
If you want to determine the solubility of a solid, say potassium nitrate in water, at any given temperature, this is how you should proceed:
Find the weight of the evaporating dish and the saturated solution.
Let this weight = ‘b’ gm.
Let this weight be ‘c’ g.
Weight of clean dry evaporating dish = ‘a’ g
Weight of dish + saturated solution = ‘b’ g
Wight of dish + solute = ‘c’ g
Weight of solute alone = (c – a) g
Weight of solvent alone = (b – c) g
Solubility of solute in solvent at that temperature
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