Properties of Dilute Solutions
Solutions may exist in any of the three states of matter that is they may be gases, liquids or solids. 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:
- Solute
- Solvent
Solute
The solute in the case of solution of a gas or solid dissolved in a liquid, is the gas or solid in other cases the solute is the component in smaller amount.
Solvent
The solvent in a solution of a gas or solid dissolved in a liquid is the liquid in other cases, the solvent is the component in greater amount.
Aqueous solutions
Solutions that contain water as the solvent are called aqueous solutions.
For example, sugar in water, carbon dioxide in water, etc.
Non-aqueous solution
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, sulfur in carbon disulphide, naphthalene in benzene, etc.Concentrated and dilute solutions
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 other that has a lesser proportion. If the proportion of solute is less, the solution is said to be dilute.
Saturated solution
A solution in which no more solute can be dissolved at a given temperature is called a saturated solution.
Unsaturated solution
A solution in which more solute can be dissolved at a given temperature is called an unsaturated solution.
A given solution that is saturated at a particular temperature may become unsaturated when the temperature is increased.
For example, the saturated and unsaturated solution of sodium chloride in water is shown below.
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.
Temperature
Increase in temperature increases the solubility.
For example, it is easier to dissolve sugar in hot milk than in cold milk.
Size of solute particles
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
Mechanical stirring increases solubility.
For example, sugar dissolves faster on stirring with a spoon.
Temperature
Increase in temperature, decreases the solubility of a solute. On heating, the gases dissolved in milk escape making the milk bubble and boil over.
Pressure
An increase in pressure increases the solubility of a gas.
For example, aerated water bottles contain carbon dioxide gas under pressure.
When sodium chloride dissolves in water the resulting uniform dispersion of ions in water is called a solution. In general a solution is a homogeneous mixture of two or more substances consisting of ions or molecules. A colloid is similar in that it appears to be homogeneous like a solution. In fact, however it consists of comparatively large particles of one substance dispersed throughout another substance or solution.
| Solutions |
States of matter |
Descriptions |
| Air | Gas | Homogeneous mixture of gases (O2, N2 and others) |
| Soda water | Liquid | Gas (CO2) dissolved in liquid (H2O) |
| Ethanol in water | Liquid | Liquid solutions of two completely miscible liquids |
| Brine | Liquid | Solid (NaCl) dissolved in a liquid (H2O) |
| Potassium-sodium alloy | Liquid | Solution of two solids (K + Na) |
| Dental filling alloy | Solid | Solution of a liquid (Hg) in a solid (Ag plus other metals) |
| Gold-silver alloy | Solid | Solution of two solids (Ag + Au) |
Gaseous solution
In general nonreactive gases or vapors can mix in all proportions to give a gaseous mixture. Fluids that mix or dissolve in each other in all proportions are said to be miscible fluids. Gases are thus miscible, (If two fluids do not mix but form two layers they are said to be immiscible). Air which is a mixture of oxygen, nitrogen and smaller amounts of other gases is an example of a gaseous solution.
For example, water and methylene chloride are immiscible and form two layers, whereas acetone and water are miscible liquids that is the two substances dissolve in each other in all proportions.
Liquid solution
Most liquids solutions are obtained by dissolving a gas, or solid in some liquid. Soda water for example, consists of a solution of carbon-dioxide gas in water. Acetone C3H6O in water is an example of a liquid-liquid solution. Brine is water with sodium chloride (a solid) dissolved in it. Seawater contains both dissolved gases (from air) and solids (mostly sodium chloride).
It is also possible to make a liquid solution by mixing two solids together. Consider a potassium-sodium alloy. Both potassium and sodium are solid at room temperature but a liquid solution results when the mixture contains 10% to 50% sodium.
Solid solution
Solid solutions are also possible. For example, dental filling alloys is a solution of mercury (a liquid) in silver (a solid) with small amounts of other metals. Gold-silver alloy is also considered as solid solutions.
