Section 8.1 Notes

Solutions: Concentration and Solubility

Solutions

• are homogeneous mixtures
• have the same appearance throughout

Alloys – a special name for solid solutions (e.g., steel)

Solute – the substance that dissolves

Solvent – the substance which does the dissolving

E.g., in sugar and water, the water is the solvent and the sugar is the solute

Water – The Universal Solvent

Water is able to dissolve many different solids, liquids and gases

Not all substances are soluble in water; e.g., fat is insoluble in water

Solubility

Solubility can be defined as:

a)      the relative ability of a solute to form a solution when added to a certain solvent

b)      the maximum amount of solute you can dissolve in a fixed amount of solvent at a given temperature

Forming a Solution

To form a solution, the solute particles must be attracted to the solvent particles; e.g., salt particles are attracted to water particles

We can say that salt is soluble in water because it dissolves in water

Salt and olive oil will not form a solution because the salt particles are not attracted to the oil particles

We can say that salt is insoluble in olive oil because it does not dissolve in olive oil

Concentration – Qualitative

A concentrated solution: A solution that contains a lot of dissolved solute compared to the amount of solvent; e.g., a can of frozen orange juice

A dilute solution: A solution that contains very little solute compared to the amount of solvent; e.g., a solution of water and the can of frozen orange juice

Concentration – Quantitative

The concentration of a solution can be written as the amount of solute dissolved in a specific amount of solvent.

For example, if 5 grams of salt are dissolved in 500 milliliters of water; the concentration is 5g/500mL

Often we reduce this to a value out of 100mL; so it can be written as 1 gram/100mL

This can also be called a 1 percent solution; this means that for 100mL of solvent there is 1g of solute dissolved in it

Saturation

Saturation: The maximum amount of solute that can be dissolved in a certain amount of solvent at a certain temperature

Saturated Solution: one that has been saturated; no more solute can be dissolved

Saturation Point: The point at which no more solute can be dissolved in a fixed volume of solvent at that temperature

If more solute can be dissolved into a solvent at a given temperature, then it is called an unsaturated solution.

Sometimes a saturated solution can be cooled below a critical temperature to form a supersaturated solution. This type of solution contains more solute that would normally be dissolved in the solution.