Parameters affecting solubility: Molecular Structure:like dissolves like" Crystal Characteristics: polymorphism,amorphous and solvates Temperature:endothemic and exoehtmic △Hsolution=△Hcrystal lattice+△Hsolvation Solubility Vs pH:Stotal=Sunionized+Sionized
Parameters affecting solubility: Molecular Structure: “ like dissolves like” Crystal Characteristics: polymorphism, amorphous and solvates Temperature: endothemic and exoehtmic Hsolution = Hcrystal lattice + Hsolvation Solubility vs pH: Stotal=Sunionized+ Sionized
Parameters affecting solubility: Molecular structure: The general rule is that"like dissolves like".A polar solvent, like water,is able to dissolve ionic solutes and other polar substances.High dipole moment,the ability to form hydrogen bonds,and the acidic or basic nature (electron donor-acceptor ability)are important characteristics to increase solubility in water. Water is a good solvent for a numerous substances: It has a high dielectric constant(that reduces the attractive forces between the atoms into a crystalline structure) It is an amphiprotic substance,acting as an acid or as a base It can solvate substances by means of dipole-dipole,ion- dipole and hyrogen bonding interactions
Parameters affecting solubility: Crystal characteristics: Polymorphism:Polimorphs are different crystalline forms of the same substance.Each form has a different crystalline lattice and different lattice enthalpies.This results in different dissolution enthalpies(Hsol).As a general rule,the less stable polimorphs have higher aqueous solubilities and hence faster dissolution rate. Amorphous:Amorphous forms(without crystalline structure)are usually more soluble compared with the crystalline form of the same substance. Solvates:Crystalline forms that include solvent molecules into the crystalline lattice.Generally the solvate has lower solubility and dissolution rate into the solvating solvent
Parameters affecting solubility: Temperature: To dissolve a crystalline solid it is neccesary to break down the crystal lattice and to solvate the formed ions.From a thermodynamic point of view this can be expressed as: △Hsolution=△Hcr+△Hsolvation △Hsolution dissolution enthalpy △HCr crystal lattice enthalpy AHsolvation solvation enthalpy AHsolvation is always 0
Parameters affecting solubility: Considering the relative magnitudes of the enthalpies, If △Hcr>△solvation then△solution>O Heat is absorbed when dissolution occurs and the dissolution is called endothermic If △Hcr<△Hsolvation then△Hsolution<O Heat is produced when dissolution occurs and the dissolution is called exothermic Cs(T1) △solution(Ti-T2) In- Cs(T2) R Ti.T2 If AHsolution 0,solubility will increase when temperature is raised If AHsolution 0.solubility will decrease when temperature is raised