A pure substance consists of a single type of particles. In other words, a substance is a pure single form of matter. However, most of the matter around us exists as mixtures of two or more pure components. Example: Sea water, minerals, soil.
Mixtures are constituted by more than one kind of pure form of matter. Based on the nature of the components that form a mixture, we have two types of mixtures:
A solution is a homogeneous mixture of two or more substances. You come across various types of solutions in your daily life. Lemonade, soda water etc. are all examples of solutions.
Solvent: The component of the solution that dissolves the other component in it (usually present in larger amount).
Solute: The component of the solution that is dissolved in the solvent (usually present in lesser quantity).
Properties of a Solution:
Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods. However, an alloy is still considered as a mixture because it shows the properties of its constituents and can have variable composition. For example, brass is a mixture of approximately 30% zinc and 70% copper.
Depending upon the amount of solute present, a solution can be called dilute, concentrated, or saturated. A saturated solution is one in which no more solute can be dissolved at a given temperature.
The concentration of a solution is the amount (mass or volume) of solute present in a given amount (mass or volume) of solution.
There are various ways of expressing the concentration of a solution, but here we will learn only three methods:
A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium.
Properties of a Suspension:
A colloid is a heterogeneous mixture, but because the size of colloidal particles is relatively small compared to a suspension, the mixture appears to be homogeneous (e.g., Milk). However, it is actually a heterogeneous mixture.
Because of the small size of colloidal particles, we cannot see them with naked eyes. But, these particles can easily scatter a beam of visible light. This scattering of a beam of light is called the Tyndall effect. The Tyndall effect can also be observed when a fine beam of light enters a room through a small hole (due to scattering by dust and smoke), or when sunlight passes through the canopy of a dense forest.
Properties of a Colloid:
The components of a colloidal solution are the dispersed phase (solute-like component) and the dispersing medium (solvent-like component).
| Dispersed Phase | Dispersing Medium | Type | Example |
|---|---|---|---|
| Liquid | Gas | Aerosol | Fog, clouds, mist |
| Solid | Gas | Aerosol | Smoke, automobile exhaust |
| Gas | Liquid | Foam | Shaving cream |
| Liquid | Liquid | Emulsion | Milk, face cream |
| Solid | Liquid | Sol | Milk of magnesia, mud |
| Gas | Solid | Foam | Foam, rubber, sponge, pumice |
| Liquid | Solid | Gel | Jelly, cheese, butter |
| Solid | Solid | Solid Sol | Coloured gemstone, milky glass |
On the basis of their chemical composition, substances can be classified either as elements or compounds.
Robert Boyle was the first scientist to use the term element in 1661. Antoine Laurent Lavoisier (1743–94) established the first useful definition of an element: An element is a basic form of matter that cannot be broken down into simpler substances by chemical reactions.
Elements can be normally divided into metals, non-metals, and metalloids.
A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion.
| Mixtures | Compounds |
|---|---|
| Elements or compounds just mix together to form a mixture and no new compound is formed. | Elements react to form new compounds. |
| A mixture has a variable composition. | The composition of each new substance is always fixed. |
| A mixture shows the properties of the constituent substances. | The new substance has totally different properties. |
| The constituents can be separated fairly easily by physical methods. | The constituents can be separated only by chemical or electrochemical reactions. |
Mastering these typical numericals will guarantee you can solve any exam question from this chapter.
Q: A solution contains 40 g of common salt in 320 g of water. Calculate the concentration in terms of mass by mass percentage of the solution.
Solution:
