Concentration and SolubilityGrade 7 Science: Pure Substances and Mixtures

Learning Goals / Success Criteria

I can describe the concentration of a solution in qualitative and quantitative terms.

I can describe the difference between saturated and unsaturated solutions.

Key terms: concentrated solution, dilute solution, concentration, saturated solution, unsaturated solution

Concentration and Solubility

Did you know apple seeds contain tiny amounts of a toxic chemical called cyanide? Eating a few of these will not harm us, but eating a large amount will have an effect on the human body.

Pure substances can be good or bad for you depending on how much of the substance you consume (think of aspirin!).

Doctors need to know how much of a substance there is in a solution when prescribing medication.

Concentration and Solubility

The words “concentrated” and “dilute” are used to describe how much solute is in a certain volume of solution.

Concentrated solution: a solution with a large number of solute particles in a given volume of solution

Dilute solution: a solution with a small number of solute particles in a given volume of solution

Concentration and Solubility

Calculating Concentration

Concentration: the amount of solute present in an amount of solution

The more solute dissolved, the greater the concentration.

This concentration can be expressed in mathematical terms: Suppose 100ml of solution contains 5.0g of sugar.

The concentration of sugar in that solution is 5.0g/100ml (a ratio!).

Calculating Concentration

The following is the equation for calculating concentration:

Concentration = mass of solute in grams

100 ml of solution

Practice: Suppose a solution contains 6.0g of sugar in 200ml of solution. What is the concentration of the sugar and water?

Saturated and Unsaturated Solutions

What would happen if you were mixing Kool-Aid and you kept adding drink powder? Eventually, no more powder would dissolve and the

solution would be saturated.

Saturated solution: a solution in which no more solute can dissolve

Unsaturated solution: a solution in which more solute can be dissolved

Solubility

We now know there is a limit to the amount of solute that can dissolve in a solvent. Chemists call this amount solubility.

Solubility: a measure of how much solute can dissolve in a solvent to form a saturated solution at a particular temperature and volume.

Different solutes have different solubilities (e.g. sugar dissolves more easily than salt) and different factors affect solubility (something you will be exploring!)