1. Composition of constituents The composition of constituent of a mixture is not fix. Air is made up of a mixture of gases. There is ___ % nitrogen gas, ___% oxygen gas and ___% carbon dioxide gas. The percent may vary from place to place. The ratio of the constituent in a compound is fixed. In a water m____, 2 hydrogen atoms chemically j___ with 1 oxygen atoms.

2. Heat change during formation Air is a mixture of many gases. During the mixing process, there is not any heat / light energy given out. The gases do not have any chemical reaction with each other. During the formation of water, H2O, hydrogen reacts with oxygen and they chemically combine together. Energy is given out, and it can be tested by a ‘pop’ sound.

3. Melting point and boiling point As the gases in the air have different mp and bp, therefore, air has a range of its mp and bp. Water has a sharp mp of 0 deg C., and a sharp bp of 100 deg C.

4. Properties The properties of air is almost the same as the properties of its constituents. E.g. oxygen supports burning and air also supports burning. The compound water has entire different properties with its constituent elements. Hydrogen can burn, oxygen supports burning, but water puts out a fire.

5. Separation Air can be separated by Fractional Distillation of liquid air under high pressure. Water cannot be broken down into its elements by physical method.