Lab: Solubility Curve of Potassium Nitrate in Water
Introduction:
Solutions are homogeneous mixtures of solvents (the larger volume of the mixture) and
solutes (the smaller volume of the mixture). For example, a hot chocolate is a solution, in which
the solute (the chocolate powder) is dissolved in the solvent (the milk or water). The solute and
solvent can be a solid, liquid, or a gas. A solution forms when the attractive forces between the
solute and the solvent are similar. For example, the ionic or polar solute, NaCl, dissolves in water,
a polar solvent. The phrase “like dissolves like” has often been used to explain this.
As the water molecules collide with the ionic compound (NaCl), the charged ends of the water
molecule become attracted to the positive sodium ions (Na+) and negative chloride ions (Cl-). The
water molecules surround the ions and the ions move into solution. This process of attraction
between the water molecules (the solvent) and the ionic compound (NaCl), the solute) is called
solvation. Solvation continues until the entire crystal has dissolved and all ions are distributed
throughout the solvent.
Solvation Process of NaCl
http://homepages.ius.edu/GKIRCHNE/Water.htm
Some solutions form quickly and others form slowly. The rate depends upon several
factors, such as, the size of solute, stirring, or heating. When making hot chocolate, we stir
chocolate powder into hot milk or water. When a solution holds a maximum amount of solute at a
certain temperature, it is said to be saturated. If we add too much chocolate powder to the hot
milk, the excess solute will settle on the bottom of the container. Generally, the chocolate
powder dissolves better in hot milk than cold milk. Thus, heating the solution can increase the
amount of solute that dissolves. Most solids are more soluble in water (solvents) at higher
temperatures.
Solubility is the quantity of solute that dissolves in a given amount of solvent. The
solubility of a solute depends on the nature of the solute and solvent, the amount of solute, the
temperature and pressure (for a gas) of the solvent. Solubility is expressed as the quantity of
solute per 100 g of solvent at a specific temperature.
