Maximum amount of substance that can be dissolved in a specific amount of solvent at a specified temperature.
Factors
- Nature of solute
- Solvent
- Temperature
- Pressure
Solubility of a solid in a liquid
- Polar solvent dissolves poar solutes
- Nonpolar solvent dissolves nonpolar solutes
- Saturated solution – solution in which no more solute can be dissolved at the same temperature and pressure is called saturated solution.
- Unsaturated solution – more solute can be dissovled at the same temperature.
- Concentration of solute in saturated solution is its solubility.
Effect of temperature
- The solution dynamic equilibrium follows Le Chateliers Principle.
- In a nearly saturated solution, the dissolution process is endothermic (Δsol H > 0) or positive.
- the solubility ncreases with rise in temperature if the dissolution is endo thermic
- if it is exothermic (Δsol H < 0), that is negative, the solubility decreases.
Effect of pressure
- No signicant role in solid – liquid or liquid – liquid solution
- Because, solid or liquid solutes have poor compressiblity
- Significant role in gas – liquid solutions
- Oxygen gas dissolves to a small extent in water. Useful for aquatic lives.
- HCl gas dissolves more in water.
- Solubility of gas in liquid increases with pressure.
Henry’s Law – at a constant temperature, the solubility of a gas in a liquid is directly proportional to the pressure of the gas.
Henry’s law is also stated that mole fraction of gas in the solution is proportional to the partial pressure of the gas over the solution. The partial pressure of the gas in vapour phase (p) is proportional to the mole fraction of the gas (x) in the solution”
Henry’s Law
- Different gases have different KH values at the sametemperature.
- That is KH (Henry’s constant) is a function of the nature of the gas.
Aquatic species are more comfortable in cold waters rather than in warm waters. Why?
Solublity of gas (oxygen) in water increases with decrease of temperature. So there is plenty of oxygen available to aquatic species.
Problem based on Henry’s Law
If N2 gas is bubbled through water at 293 K, how many millimoles of N2 gas would dissolve in 1 litre of water. Assume that N2 exerts a partial pressure of 0.987 bar. Given that Henry’s law constant for N2 at 293 K is 76.48 kbar.
