Shaillee Kaushal is teaching live on Unacademy Plus
XII -02 Solutions Ill
SOLUTION OF GASES N LIQUID o Solutions of gases in water play an important role in our daily life. The common examples are soft drinks, household cleaners containing aqueous solutions of ammonia, the natural waters contains dissolved which is vital for aquatic life. o The solubility of a gas in a liquid is expressed in absorption co-efficient. lt is defined as the volume of the gas in mL that can be dissolved by 1mL of liquid solvent at the temperature of the experiment at one atmospheric pressure.
Mathematically absorption co-effiecient ' i s given by v volume of the gas dissolved VP V volume of the solvent P pressure of the gas in atmosphere
Factors on which solubility of gases in liquid depen<d Nature of the gas and solvent . Gases which are easily liquified are more soluble. For example CO2 is more soluble than oxygen. Also the gases which react with solvent posess higher solubility. For example, HCl and NH3 are highly soluble in water. . Oxygen, nitrogen and carbondoxide are more soluble in ethyl alcohol than in water.
Temperature: As the process of dessolution of gases is an exothermic process therefore the solubility of gases decreases with increase in temperature >This is the reason why aquatic animals are not very comfortable in warm water as the solubility of oxygen decreasing with increase in temperatrue.
Pressure This is the most important factor that influences the solubility of a gas in a liquid. >The effect of pressure on solubility of gases is given by Henry's law. It states that the solulbility of a gas in a liquid is directly proportional to the pressure of the gas over the solution at a definite temperature According to this law m- mass of the gas dissolved per unit volume of the solvent m-KP Ppressure of the gas K- proportionality constant
The volume of K is different for each gas at a particular temperature If the solubility of the gas is known at one particular pressure, then it can be calculated at other pressure: m1P m2 m P2 solubility of the gas at pressure P m2 solubility of the gas at pressure P2 The law can also be stated in terms of mole fraction as: x mole fraction of the gas P = Partial pressure of the gas KH Henry's constant
Different gases have different values of KH at different temperatures Values of Henry's law constant (KH) for some common gases in water. Gas Temperature (K) 293 293 293 303 293 393 KH (K bar) 144.97 69.16 76.48 88.48 34.86 46.82 2 0 0 2 Higher the values of Henry's law constant lower is the solubility of the gas in liquid Limitations of Henrv's law The law holds good if the following conditions are fulfilled (i) The pressure is not too high (ii) The temperature is not very low (ii) The gas does ot chemically combine with the sovent. If the gas reacts with the solvent, higher solubilities may result. As the solubility of NH3 and CO2 is much more in water than expected. Also oxygen dissolves in haemoglobin to great extent as it reacts with haemoglobin
Applications of Henry's law 1. Soft drink bottles are sealed at high pressrue to increase the solubility of CO2 2. At high altitude, partial pressure of oxygen is low leading to low concentration of oxygen in blood. This results in anoxia i.e unable to think and act properly. 3. When Scuba divers go deep in the sea, solubility of atmosphere gases increase in the blood. When the divers come up the dissolved gases are suddenly released which leads to formation of bubbles of nitrogen causing a painful sensation bends'. In order to resolve this problem the tanks of scuba divers are filled with 11.7% He, 56.2% N, and 32.1 % oxygen Salting out effect:_Gases are less soluble in aqueous solutions than pure water. This is called salting out effect