Concentration terms such as mass percentage, ppm, mole fraction and molality are independent of temperature, however molarity is a function of temperature. Explain.
Molarity is defined as the number of moles of solute dissolved per litre of a solution. Since, volume depends on temperature and changes with change in temperature, the molarity will also change with change in temperature.
On the other hand, mass does not change with change in temperature, so other concentration terms given in the question also do not do so. Thus, temperature has no effect on the mass but it has significant effect on volume.
What is the significance of Henry's law constant $\mathrm{K}_H$ ?
According to Henry's law $p \propto x \Rightarrow p=K_H x$
Higher the value of Henry's law constant $K_H$, the lower is the solubility of the gas in a liquid. Thus, the solubility of a gas in the given liquid can be increased by increasing pressure.
Why are aquatic species more comfortable in cold water in comparison to warm water?
Aquatic species are more comfortable in cold water due to the presence of more oxygen. Solubility of oxygen in water increases with decrease in temperature as solubility of a gas in given liquid decreases with increase in temperature.
(a) Explain the following phenomena with the help of Henry's law.
(i) Painful condition known as bends.
(ii) Feeling of weakness and discomfort in breathing at high altitude.
(b) Why soda water bottle kept at room temperature fizzes on opening?
(a) (i) Henry's law represents a relation between solubility of gases in liquid and pressure. Scuba drivers when comes towards surface, the pressure gradually decreases. This reduce pressure releases the dissolve gas present in blood and leads to formation of bubbles of nitrogen in the blood.
This creates a painful condition by blocking capillaries known as blends.
(ii) At high altitude atmospheric pressure is low as compared to surface which causes difficulty in breathing. On that condition we feel weakness and discomfort.
(b) Soda water bottle kept at room temperature fizzes on opening due to different pressure inside and outside the bottle. When the bottle is opened to air, the partial pressure of $\mathrm{CO}_2$ above the solution decreases. As a result, solubility decreases and hence $\mathrm{CO}_2$ bubbles out.
Why is the vapour pressure of an aqueous solution of glucose lower than that of water?
In pure liquid, the entire surface of liquid is occupied by the molecules of water. When a non-volatile solute, e.g., glucose is dissolved in water, the fraction of surface covered by the solvent molecules gets reduced because some positions are occupied by glucose molecules.
So, number of solvent molecules escaping from the surface is reduced. That is why vapour pressure of aqueous solution of glucose is reduced.