Comparing the solubility's of copper sulphate, sodium chloride and potassium nitrate
Comparing the solubility's of copper sulphate, sodium chloride and potassium nitrate
Background Information
Molecular solids (sugar) and ionic solids (salts) both dissolve in water. However, they both dissolve in different ways.
The intermolecular forces holding molecules of sugar together are relatively weak so when sugar is placed in water these bonds are broken and individual C12H22O11 molecules are released into solution. It takes energy to break bonds between C12H22O11 molecules and it also takes energy to break the hydrogen bonds in water. These hydrogen bonds have to be disrupted in order to insert a sugar molecule into the substance. The energy needed for this is produced by the forming of bonds between slightly polar sucrose molecules and polar water molecules. This process works so well between sugar and water that up to 800g of sugar can dissolve in 1 litre of water.
The positive and negative ions in ionic solids (or salts) are held together by the strong force of attraction between particles with opposite charges. When a salt dissolves in water the ions are released and become associated with the polar solvent molecules. Salts dissociate with their ions when they dissolve in water.
H2O
e.g. NaCl (s) Na+ (aq) + Cl (aq)
There are several factors that will affect solubility between different compounds:
Temperature - If the solution process absorbs energy then the solubility will be
increased if there is a temperature increase. If the solution
releases energy (exothermic, i.e. between sugar and water)
then solubility will decrease.
Molecular Size - If the size or weight of the individual molecules is large then
solubility will be low because larger molecules are difficult to
surround with solvent molecules.
Polarity - Generally only polar solute molecules will dissolve in polar solvents
and only non-polar solute molecules will dissolve in non-polar
solvents. Polar solute molecules have positive and negative ends.
So if a polar solute molecule is placed in a polar solvent then the
positive ends of solvent molecules will attract the negative ends of
solute molecules. This type of intermolecular force is known as di-
pole-dipole interaction. The type of intermolecular force in present in
non-polar molecules is called London Dispersion forces. Here the
positive nuclei of the atoms of the solute molecules will attract the
negative electrons of the atoms of a solvent molecule.
Branching - This factor only applies to organic compounds. The amount of
carbon branching will increase solubility because more branching will reduce the size of the molecule, making it easier to solvate.
