Solutions and solubility
In our daily life, we are surrounded by diﬀerent types of solutions. A solution consist of a solute and a solvent. A solute is a substance that dissolves in a solvent. for example, in a salt (NaCl) solution, the salt crystals are the solute. A solvent is the substance theat dissolves the solute. For example in NaCl solution, the solvent would be the water
A solute is a substance that is dissolved in another substance. A solute can be a solid, liquid or gas. A solvent is the liquid that dissolves a solid, liquid, or gaseous solute.
Types of solutions
When a solute is mixed with a solvent, a mixture is formed, and this may be either heterogeneous or homogeneous. If you mix sand and water for example, the sand does not dissolve in the water. This is a heterogeneous mixture. When you mix salt and water, the resulting mixture is homogeneous because the solute has dissolved in the solvent.
Solution In chemistry, a solution is a homogeneous mixture that consists of a solute that has been dissolved in a solvent.
A solution then is a homogeneous mixture of a solute and a solvent. Examples of solutions are:
- A solid solute dissolved in a liquid solvent e.g. sodium chloride dissolved in water. •
- A gas solute dissolved in a liquid solvent e.g. carbon dioxide dissolved in water (ﬁzzy drinks) or oxygen dissolved in water (aquatic ecosystems).
- A liquid solute dissolved in a liquid solvent e.g. ethanol in water. • A solid solute in a solid solvent e.g. metal alloys.
- A gas solute in a gas solvent e.g. the homogeneous mixture of gases in the air that we breathe.
While there are many diﬀerent types of solutions, most of those we will be discussing are liquids.
Forces and solutions
An important question to ask is why some solutes dissolve in certain solvents and not in others. The answer lies in understanding the interaction between the intramolecular and intermolecular forces between the solute and solvent particles.
- Non-polar solutes and non-polar solvents (e.g. iodine and ether) Iodine molecules are non-polar, and the forces between the molecules are weak van der Waals forces. There are also weak van der Waals forces between ether molecules. Because the intermolecular forces in both the solute and the solvent are similar, it is easy for these to be broken in the solute, allowing the solute to move into the spaces between the molecules of the solvent. The solute dissolves in the solvent.
- Polar solutes and polar solvents (e.g. salt and water) There are strong electrostatic forces between the ions of a salt such as sodium chloride. There are also strong hydrogen bonds between water molecules. Because the strength of the intermolecular forces in the solute and solvent are similar, the solute will dissolve in the solvent.
You may have noticed sometimes that, if you try to dissolve salt (or some other solute) in a small amount of water, it will initially dissolve, but then appears not to be able to dissolve any further when you keep adding more solute to the solvent. This is called the solubility of the solution. Solubility refers to the maximum amount of solute that will dissolve in a solvent under certain conditions.
Solubility is the ability of a given substance, the solute, to dissolve in a solvent. If a substance has a high solubility, it means that lots of the solute is able to dissolve in the solvent.
So what factors aﬀect solubility? Below are some of the factors that aﬀect solubility:
- The quantity of solute and solvent in the solution
- The temperature of the solution
- Other compounds in the solvent aﬀect solubility because they take up some of the spaces between molecules of the solvent, that could otherwise be taken by the solute itself
- The strength of the forces between particles of the solute, and the strength of forces between particles of the solvent.