Solution

Solutions are homogeneous mixtures of two or more substances. The substance present in the lesser amount is called the solute. The substance present in the greater amount is called the solvent. A common solvent that is used is water. However, there are other solvents such as acetone, hexane, methanol that are commonly used as cleaners and to dissolve grease.

Solutions are not only limited to liquid solutions. For example:

• air is a gaseous solution of oxygen, argon, carbon dioxide, and water vapor in nitrogen gas.
• 10K gold is a solid solution of silver,copper and zinc in gold.
• carbonated soft drinks is a liquid solution of carbon dioxide gas, sugar in water.
• vinegar is a liquid solution of vinegar in water.

Soluble/Insoluble

Sugar is soluble in water. This means that you can dissolve a large quantity of sugar into water. How much is "a large quantity"?

We use the term solubility to quantify the amount of solid solute will dissolve in a given quantity of solvent at a specific temperature.

The solubility of sodium chloride, table salt, is 36 grams per 100 grams of water at 20°C.

When a substance does not dissolve in a solvent, it is insoluble. View the solubility rules. Many compounds such as AgCl, Hg₂Cl₂, PbCl₂, BaSO₄, SrSO₄, PbSO₄ are insoluble in water. Become familiar with the compounds that are listed on the table of the solubility rules and be able to recognize the types of compounds that are soluble or insoluble in water.

Solubility of covalent compounds

Liquids that have covalent bonding are classified into two types:

• polar
• nonpolar

We can determine whether a liquid is polar or nonpolar by determining whether the molecule possesses a net dipole moment. For example, water is a polar liquid.

In general, "like dissolves like" describes the general principle of solubility (i.e. polar solvents dissolve polar solutes and non-polar solvents dissolve non-polar solutes).

Polar solutes are soluble in water, while nonpolar solutes are insoluble in water.

Solubility of ionic compounds

in aqueous solution, an ionic compound dissociates into its ions and giving the solution the ability to conduct electricity. Any substance that gives ions in an aqueous solution and thereby conducts electricity is called an electrolyte.

As an ionic solid such as NaCl dissolves in water, water molecules must overcome the forces which hold ions together to make them go into solution. The polar water molecules are attracted to both positive and negative ions of the ionic solid.

Look carefully at the above diagram and see that the positive ions are attracted by the oxygen atom of the water and the negative ions are attracted by the more positive hydrogen atoms of water. Once an ion is surrounded by the water molecules, an ion is freed from the lattice and a hydrated ion is formed.

The process of going into solution may be exothermic or endothermic.

External link

Strong electrolyte, weak electrolyte, nonelectrolyte

Sodium chloride dissolving in water

Miscible/Immiscible

Miscible and immiscible describes what happens when two liquids are brought in contact with each other. Liquids such as gasoline, water and mercury are immiscible. The three liquids separates into three distinct layers, with the liquid that is the most dense on the bottom. Liquids such as water and ethyl alcohol are miscible. This means that the two liquids dissolves in one another and there are no separation of layers observed.

Polar liquids are miscible in water, while nonpolar liquids are immiscible in water.

Saturated/Unsaturated

When a solution contains as much dissolved solute as it can hold at a given temperature and has undissolved solute in the solution, the solution is said to be a saturated solution.

The solubility of sodium chloride, table salt, is 36 grams per 100 grams of water at 20°C.

When we place 40 grams of table salt in 100 grams of water at 20°C, 36 grams will become dissolved in water. The remaining undissolved crystal will remain as a solid in the solution. This is a saturated solution. However, solubility increases with temperature. This means that at higher temperature, the solubility of table salt is greater than 36 grams in 100 grams.

If we increase the temperature to 30°C, the remaining 4 grams of undissolved table salt crystal will dissolve into the solution. At 30°C, this solution contains less solute than the solubility limit. Therefore, at 30°C, this solution becomes unsaturated.

Content suitability

BCIT courses: CHEM 0011