Solution

Mixtures are around us.  We encountered them everyday.  Mixtures are either homogeneous and heterogeneous.  The homogeneous mixture is what we called solution.  Some examples of solutions are seawater, sugar in water, alcohol solution, and more.  Solutions maybe solid, liquid or gas.

Solution is a homogeneous mixture composed of solute and solvent.  Solute is a component present in smaller quantity while the solvent is a component present in greater quantity.  Solute and solvent can vary their quantities.  Example, alcohol solution can be 30% by volume and 70% by volume. A 30% alcohol solution means that in every 100 mL of the alcohol solution, contains 30 mL of alcohol and 70 mL water, while a 70% alcohol solution means there is 70 mL alcohol and 30 mL water.

Types of Solution

Solutions are classified into three types: the solid solution, liquid solution and the gaseous solution.  The type of solution can be identified based on their solvent.  If the solvent is liquid the solution is liquid, if the solvent is solid the solution is solid and if the solvent is gas the solution is a gaseous solution.  Below are some examples of solutions and their types.

Solution can also be characterized by their capacity to dissolve a solute.  We have saturated solution, a solution in which contains maximum amount of solute in a given solvent, at a specific temperature. Unsaturated solution contains less solute than it has the capacity to dissolve in a given solvent, at a specific temperature. Supersaturated solution contains more than the maximum amount of solute that it can dissolve in a given amount of solvent, at a specific temperature.  Supersaturated solution is not very stable.  In time, some of the solute will come out from the solution as crystals.  The process is called crystallization.  Crystallization is a process in which dissolved solute comes out of solution and forms crystals.

The Solution Process

Solution is formed when the solute disperses uniformly in the solvent.  That is when the attractive forces between solute and solvent particles are comparable in magnitude with those that exist between the solute particles themselves or between the solvent particles themselves.  For example, when NaCl dissolves readily in water, the attractive interaction between the Na⁺ ions and Cl^- ions and the polar H₂O molecules overcome the lattice energy of NaCl.

Below shows a molecular view of solution process taking place in three steps.  Step 1 is the separation of solvent molecules; step 2 also shows the separation of solute; and the step 3, is the mixture of solute and solvent.

Below shows what happens when NaCl is dissolved in water:

The picture shows that when NaCl is dissolved in water, the water molecules orient themselves on the surface of NaCl crystals.  The positive end of the water dipole is oriented toward the Cl- ions, and the negative end of the water dipole is oriented towards the Na+ ions.  The ion-dipole attraction between the ions and the water molecules are sufficiently strong to pull the ions in NaCl crystals.