Give reasons
(a) Even when the water at the surface of a lake is frozen, aquatic animals continue to live below the ice.
(b) It is easier to swim in sea water.
(c) Water is said to be a universal solvent.
(d) Water is an ideal medium for chemical reactions.
Give reasons
(a) Even when the water at the surface of a lake is frozen, aquatic animals continue to live below the ice.
(b) It is easier to swim in sea water.
(c) Water is said to be a universal solvent.
(d) Water is an ideal medium for chemical reactions.
(a) The water expands from 4oC to 0oC (density decreases with decrease in temperature) and stops the convection currents in the water. The top layer expands and freezes, while the water in the lower levels remains at 4oC. As ice is a poor conductor of heat, further freezing by conduction or convection is not possible. Hence, at 4oC aquatic animals can continue to live below the ice.
(b) The density of the sea water is more than the density of the river water because of the large amount of dissolved salts in it. So, while swimming the weight of displaced sea water is more than the weight of displaced river water. This weight gives the upward buoyant force to the swimmer. Thus, the apparent weight of the swimmer is less in the sea water. Hence, it is easier to swim in the sea water than the river water.
(c) The major reason for which water is referred to as a universal solvent is indeed because of its ability to dissolve many substances. It is one of those compounds whose solid state has less density than the liquid state. Also, it is colourless, and has no taste and odour. It is the only natural substance that is found in all the three states viz. solid (ice), liquid (water) and gaseous (water vapours) state. Water can dissolve many substances because of its high polarity. The dielectric constant of water is 81, which is the highest for any solvent and hence, it can dissolve many substances. Water molecules can easily break the bonds between the molecules of substances and therefore dissolve them.
(d) Water has several properties, which makes it ideal for chemical reactions.
(i) High specific heat - Water absorbs a great deal of heat for every molecule of water present because of the large amount of Hydrogen Bonds.
(ii) Polarity - Water is a polar molecule. This allows it to dissolve any other polar molecule because it has both a negatively charged and a positively charged end.
(iii) Neutral pH - Water is the basis for the pH scale with a neutral pH of 7.
(a) The water expands from 4oC to 0oC (density decreases with decrease in temperature) and stops the convection currents in the water. The top layer expands and freezes, while the water in the lower levels remains at 4oC. As ice is a poor conductor of heat, further freezing by conduction or convection is not possible. Hence, at 4oC aquatic animals can continue to live below the ice.
(b) The density of the sea water is more than the density of the river water because of the large amount of dissolved salts in it. So, while swimming the weight of displaced sea water is more than the weight of displaced river water. This weight gives the upward buoyant force to the swimmer. Thus, the apparent weight of the swimmer is less in the sea water. Hence, it is easier to swim in the sea water than the river water.
(c) The major reason for which water is referred to as a universal solvent is indeed because of its ability to dissolve many substances. It is one of those compounds whose solid state has less density than the liquid state. Also, it is colourless, and has no taste and odour. It is the only natural substance that is found in all the three states viz. solid (ice), liquid (water) and gaseous (water vapours) state. Water can dissolve many substances because of its high polarity. The dielectric constant of water is 81, which is the highest for any solvent and hence, it can dissolve many substances. Water molecules can easily break the bonds between the molecules of substances and therefore dissolve them.
(d) Water has several properties, which makes it ideal for chemical reactions.
(i) High specific heat - Water absorbs a great deal of heat for every molecule of water present because of the large amount of Hydrogen Bonds.
(ii) Polarity - Water is a polar molecule. This allows it to dissolve any other polar molecule because it has both a negatively charged and a positively charged end.
(iii) Neutral pH - Water is the basis for the pH scale with a neutral pH of 7.
