Is matter around us pure notes (part 2)
Suspension
Suspension is a mixture in which the particles are suspended in a dispersion medium. They contain relatively large particles.
- Example: Clay in water.
Water is a compound and not a mixture
- The components hydrogen and oxygen cannot be separated by physical methods such as filtration, evaporation.
- Hydrogen and oxygen are present in a fixed proportion of 1: 8.
- Energy changes accompany the formation of a compound i.e., heat and light are given out.
- Properties of water are entirely different from the constituents, hydrogen and oxygen.s
- The boiling point of water is 100oC at 76 cm Hg i.e., one atmospheric pressure.
Differences between mixtures and compounds
| Mixtures | Compounds |
| A mixture can be separated into its constituents by physical processes (filtration, evaporation, sublimation, distillation) | A compound cannot be separated into its constituents by physical processes. It can be separated by chemical means |
| A mixture shows the properties of its constituents | A compound has a new set of properties different from its constituents |
| Composition of a mixture varies and the constituents are present in any proportion by weight. It does not have a definite formula | The composition of a compound is fixed and the constituents are present in fixed proportions by weight. It has a definite formula |
| The constituents do not react chemically, thus no energy changes take place | Chemical reactions take place and energy changes in the form of heat and light are involved |
| A mixture does not have a fixed melting point and boiling point Examples: air, sand and salt | A compound has a fixed melting point and boiling point Examples: H2O (water), FeS (iron sulphide) |
Purification of surface water
Physical Change
When the shape, size, appearance or state, of a substance is altered, but its chemical composition remains same a physical change of matter takes place. No new substance is formed. It is usually a change, which is reversible. Such as: preparing a solution, breaking a glass tumbler, glowing a electric bulb, etc.
Examples of Physical Changes
- By using a piece of gold, a goldsmith can make a gold chain and can later alter it to make a gold bracelet, ring or a pair of earrings. All of them consist of the same substance, namely gold. This is an example of a physical change.
- A more common everyday example is that of water, which can be converted into solid ice, liquid water, and gaseous water vapour. It can be reconverted to its previous state by various methods. Yet, in all the three forms, the chemical composition of water is not altered. No new substance with new chemical properties is formed. In all these, water consists of two atoms of hydrogen and one atom of oxygen.
- Dissolving of sugar in water when crystalline sugar is dissolved in water, it seems to disappear completely and not even a very powerful microscope can show us the molecules of sugar in water. The solution obtained is uniformly sweet. By evaporating the water the sugar can be recovered in a crystalline form.
A physical change involves a change in the physical state of a substance by changing either the inter particle spaces or inter particle forces.
- There is no change in the composition of the substances during the physical change.
- The substances undergoing physical changes do not change their main characteristics.
- No new substance is formed during physical change.
- The change is temporary and can be reversed by reversing the conditions which bring about the change.
Chemical change
A change in which the composition of a substance is altered is called as chemical change of matter. As a result, the original properties get changed and one or more new substances are formed. Such as: rusting of iron, burning of magnesium ribbon, burning of a piece of paper, etc.
Characteristics Associated with Chemical Changes
- As a result of chemical change, the physical state of the substance may or may not change.
- There is always a change in the chemical compositions of the substance.
- There is also change in characteristics of the substance.
- New substances are always formed
- The chemical change is of permanent nature and cannot be easily reversed.
Solutions
Solution is defined as a homogeneous mixture of two or more chemical substances.
- A Solution is a homogeneous mixture of two or more substances. These substances can be in any of the three physical states. 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
- There are two types of solution: Aqueous solutions & Non-aqueous solutions. 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 solutions: 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.
General properties of solution
- Appearance: Clear and transparent, especially in dilute form.
- 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.
- 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.
- 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.
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.