Some of the most important properties of pure water are :
Physical Properties of Pure Water:
Pure water is a colorless, tasteless and odorless liquid. Distilled water is pure. Drinking water has a pleasant taste because dissolved minerals and air in water make its taste better.
Pure water exists in all the three states as solid (ice), liquid (water) and gaseous (steam or water vapor).
3. Freezing point of water:
Pure water freezes to solid ice at 00C (at 760 mm of mercury pressure)
If water contains impurities, it freezes at a temperature less than 00C. Presence of impurities lowers the freezing point. Also, at a higher pressure, water freezes at a temperature slightly less than 00C. That is why, on mountains (at a lower atmospheric pressure), water freezes at a temperature slightly higher than 00C.
4. Boiling point of water:
Pure water boils at 1000C (at 760 mm of mercury pressure).
At high pressure, the boiling point is more than 1000C. when pressure is high, molecules of water vapour cannot escape easily from the surface. This is why food cooks faster in a pressure cooker. At low pressures (or on high mountains), water boils at a temperature slightly less than 1000C. This is so because water molecules are more free to escape from the water surface.
5. Stable substance:
Water is a stable substance. It is broken into its components H2 and O2 when we heat water beyond 5000C. Alternatively, electrolysis breaks molecules of water into H2 and O2.
During freezing and boiling, the molecules of water are not broken down.
6. Anomalous expansion:
Normally, a substance expands on heating and contracts on freezing but with water it is just the opposite, when heated or cooled between 40C and 00C.
i. On cooling below 40C, water expands and hence its volume increases. So, the volume of ice at 00C is greater than the volume of water at 00C. Water contracts from 00C to 40C and then expands as usual with rise in temperature.
ii. On heating water at 00C, water contracts and hence its volume decreases. This happens up to 40C. On freezing water, its volume increases by about 10%.
Density of solid water, i.e., ice is lower than the density of liquid water at room temperature. That is why ice cubes float in water. Hence, is lighter than water.
Density of a substance is defined as its mass per unit volume
Pure water has the maximum density at 40C and minimum density at 00C. Ice is lighter and floats in water.
Hence, pure water has a minimum volume at 40C and maximum volume at 00C. very cool water at around 40C is the most packed arrangement.
It means that for the same mass of ice and water, the volume of ice is more than that of water. In other words, size of water increase on solidification while mass remains the same.
Therefore, water expands in volume when it is solidified to ice. But with ghee or oil it is just the opposite; they expand on heating and contract on freezing. Normally 1 cm3 (c.c.) of water has a mass of 1 gram. That is, the density of water is 1g/cm3.
8. Heat capacity of water:
Heat capacity of a substance is the heat required to raise its temperature by one degree. Heat capacity of water is highest among all liquids.
9. A good solvent:
Water is an excellent solvent. It dissolves many substances forming aqueous solutions. Therefore, it is known as ‘universal’ solvent. A solution of a substance in water is known as an aqueous solution [aqueous means watery].
10. Bad conductor of heat and electricity:
Water does not conduct heat and electricity well.