According to Henry’s Law, mass of the gas dissolved in a given volume of a liquid is directly proportional to the pressure of the gas. This is called Henrys law in solutions
Solubility of O2 gas of the air in water is called dissolution of O2 which forms the basis of survival of aquatic life.
Solubility of gas in a liquid ( Gaseous solutions )
Gaseous solutions is defined as volume in cc (STP) of the gas that can be dissolved in 1 cc of liquid to form the saturated solution. Solubility here, is expressed in terms of molarity or mole fraction of the gas.
Factors affecting the solubility of a gaseous solution
- Nature of gas and the solvent Gases like H2, O2, N2 dissolve in water to a less extent and CO2, HCl, and NH3 are highly soluble in water.
2. Effect of temperature Dissolution of a gas in a liquid is an exothermic reaction. According to Le-Chatelier’s principle, increase of temperature will shift the equilibrium in the backward direction. This means the solubility decreases if we increase the temperature in case of exothermic reaction.
Gas + solvent = Solution + heat
3. Effect of Pressure Henry’s law: According to Henry’s Law, mass of the gas dissolved in a given volume of a liquid is directly proportional to the pressure of the gas. PA = KH * XA where, PA is the pressure of the gas A , KH is the Henry’s constant and XA is the mole fraction of the gas in the solution.
(i) KH is the function of the nature of the gas
(ii) Greater is the value of KH, lower is the solubility of the gas at the same pressure.
(iii) The value of KH increases with the increase of temperature. The solubility decreases with increase of temperature at the same pressure. This is because aquatic species feel more comfortable in cold water ( more dissolved O2 ) than in warm water ( less dissolved O2 )
Limitations of Henry’s Law :
- Pressure should be low and the temp should be high like an ideal gas.
- The gas should not undergo association or dissociation with the solvent.
Applications of Henry’s Law :
(i) In the deep see diving
Scuba divers carry compressed air for their O2 supply. As the divers goes deep in the sea, with the increase of pressure, the solubility of N2 and O2 gets more dissolved in the blood. When the diver comes back to the sea surface then N2 forms bubbles to give decompression sickness. To avoid this condition, scuba divers carry air diluted with He.
(ii) In the production of carbonated beverages
CO2 gas is dissolved in soft drinks under high pressure. When the bottle is opened to air, the gas fizzes out. As the pressure above the solution decreases, solubility of CO2 decreases and it comes out in the form of bubbles.
(iii) For climbers living at high altitude
At higher altitude, as the atmospheric pressure decreases, partial pressure of O2 is less in air. As a result, less concentration of O2 is dissolved in the blood at the higher altitudes. The climbers feel lack of energy and unable to think properly due to improper supply of O2 to the brain.
(iv) In the functioning of Lungs
When O2 enters in to the lungs, it combines with haemoglobin to form oxyhaemoglobin. Partial pressure of O2 in tissues is low. Therefore, O2 gas is released from the complex oxyhaemoglobin to the living cells of the body.
FAQs related to Henry’s Law in solutions :
- In which condition Henry’s Law is not applicable ?
Answer : Henry’s Law is not applicable when the gas is under high pressure and gas shows any dissociation or association with the solvent molecule.
2. Why Henry’s Law is not applicable at high pressure ?
Answer : When the pressure is high, the molecules comes closer together. This results in the attraction between the molecules of gas at higher pressure.
3. Is Raoult’s Law a special case of Henry’s Law ?
Answer : Both of the laws states that partial pressure of the volatile component is directly proportional to its mole fraction in the solution.
4. Which solution obeys Henry’s Law ?
Answer : An ideal solution obeys Henry’s solution in which solute-solute concentration is similar to solute-solvent concentration.
5. Which of the gases in water is valid for Henry’s Law ?
Answer : NH3 and CO2 can form H-bonding with water and follows Henry’s Law.
You can also learn the concentration of solutions. from here.
to explain the content and try some of the numericals from solutions
You can also read the articles on the structure and bonding of some simple molecules like H2O
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