Factors Affecting Solubility

Solubility is defined as the maximum amount of solute that will dissolve in a given amount of solvent at a specific temperature.  A solution which contains the maximum amount of solute is said to be saturated.  Solutes have different solubility in water and are affected by some factors.  For example, the solubility of NaCl in water at 0^oc is 35.7 g per 100 mL   This means that at 0^oC only 35.7 g of NaCl can dissolve in 100 mL of water.  Adding more solute to the solution will not anymore dissolve the solute.  Below is a graph showing the solubility of some salts:

Temperature

Temperature is one of the factors that affects the solubility of solute in a given solvent.  The solubility of solid in liquid is different with that of gas in liquid solution, which we need to emphasize.  For solid in liquid solution like salt in water, generally the solubility increases as the temperature increases,   except for some exceptions.  For example in the solubility versus temperature graph shown above, almost all salts increases solubility as the temperature increases, only Ce₂(SO₄)₃ decreases its solubility.

For gas in liquid solution, the increase in temperature results in decrease in solubility.  Example, carbonated drinks contains carbon dioxide dissolved in water.  It is usually placed inside the refrigerator to increase its solubility.  Try boiling carbonated drinks and compare its taste to the original mixture, and you will find a big difference in their taste, once heated the carbon dioxide dissolve in water comes out from the water and result in decrease in solubility

Pressure

Pressure does not affect all types of solutions, only in gas in liquid solution, like carbonated drinks.
Try opening a bottle of soft drinks and observe what happens.  An effervescence  indicates that there is  gas that comes out from the solution.  Opening the bottle means you decrease the pressure and the solubility also decreases.  The quantitative relationship between pressure and solubility is given by Henry's Law, which states that the solubility of a gas in a liquid is proportional to the pressure of the gas over the solution.

c  ∝  P

c  =  kP

where c is the molar concentration in mole per liter of the dissolved gas;  P is the pressure in atmosphere of the gas over the solution; and for a given gas, k is a constant that depends on temperature.  The constant k has the unit mol/liter . atm.  

Nature of Solute and Solvent

The solubility of some solids and liquids follow the general rule like dissolves like.  Solutes and solvent can be polar, nonpolar or ionic.  Like dissolves like means polar solvent dissolves polar solutes and ionic solutes and nonpolar solvent dissolves nonpolar solutes.  The stronger the attraction between solute and solvent the higher the solubility.  For example, kerosene is immiscible in water, simply because they have different polarity, whereas if we will combine kerosene and gasoline, there is a complete dissolution that occurs because of similar nature of the two substances.