Two or more substances in a homogeneous mixture constitute a solution. The substance that is dissolved into another substance is the solute. The substance that dissolves is known as the solvent. Aqueous solutions are the most common solutions in biochemistry. There are several ways to represent the concentration of a solution.
| Term for Concentration | Definition |
| Weight Percent | (wt/wt) = mass of solute/mass of solution x 102 |
| Parts per Thousand | (ppt) = mass of solute/mass of solution x 103 |
| Parts per Million | (ppm) = mass of solute/mass of solution x 106 |
| Parts per Billion | (ppb) = mass of solute/mass of solution x 109 |
| Volume Percent | (v/v) = volume of solute/volume of solution x 102 |
| Mole Fraction Solute | (Xsolute) = moles of solute/(moles of solute + moles of solvent) |
| Mole Fraction Solvent | (Xsolvent) = moles of solvent/(moles of solute + moles of solvent) |
| Molality | (m) = moles of solute/mass (in kilograms) of solvent |
| Molarity | (M) = moles of solute/volume (in Liters) of solution |
There are several factors affecting solubility. These factors include: intermolecular forces, temperature, pressure. If a solute is going to be soluble in a particular solvent, the interactions between the intermolecular forces holding the solvent molecules together must be overcome to make room for the solute. Likewise, the intermolecular forces holding the solute together must be overcome. Overcoming intermolecular forces requires energy. Solvation energy is the energy released when the solute and the solvent interact. The rule “like dissolves like,” refers to intermolecular forces in a solution (H bonding, dipole-dipole, or London forces. The solubility of a liquid or solid tends to increase with increasing temperature.
General-Organic-Biochemistry 