Science Focus Topic 2 Notes: Mixing and Dissolving | Print |

Classification of Matter

- All pure substances have their own unique set of properties, or characteristics
- All mixtures contain two or more pure substances, which have their own distinct properties (some of which may be hidden)

Homogenous Mixtures

- are mixtures which look as though they have only one set of properties.
- the blended mixture has equal amounts of both substances (all parts of the mixture are the same)
- if the homogenous mixture does not have any settling of any of the substances it is made of, then it is called a solution
- solutions occur because each particle slips between each other particle and is evenly distributed throughout the entire mixture

Homogenous Mixtures

- the properties of the pure substances, in a heterogeneous mixture, are not hidden
- if there are two or more materials that are visible within a mixture, then it is called a heterogeneous mixture

In-Between Mixtures

- a heterogeneous mixture, in which the particles settle slowly after mixing, is called a suspension (eg. orange juice)
- a heterogeneous mixture, in which the particles do not settle at all, is called a colloid (eg. fog)
- to disperse the particles for a longer period of time, an emulsifying agent (like a protein) is used to form an emulsion (eg. mayonnaise)
- mixtures that are obviously two or more substances are called mechanical mixtures
the separate parts of the mechanical mixture are called phases


What Makes Materials Dissolve?

- forming a solution by mixing two or more materials together is called dissolving
- dissolving occurs because of the attracting between the particles (there may be a stronger attraction to the particles of another substance, than to the particles of the same substance)

Solutes and Solvents

The solute is the substance that dissolves in a solvent. The solvent is the substance that dissolves the solute to form a solution.
Soluble means to be able to be dissolved in a particular solvent. Solutes and solvents can be gases or liquids.

Water - the Universal Solvent

- it is called the 'universal solvent' because it can dissolve so many materials
- 97% of the water on Earth is Ocean water, 2% is frozen and only about 0.5% is 'usable' (and even this has materials already dissolved in it that can be harmful

The Rate of Dissolving

- the speed at which the solute dissolves in a solvent is called the rate of dissolving and can be affected by:
- agitation (stirring or shaking)
- temperature
- pressure

How Much Can Be Dissolved?

- the limit to concentration is called solubility
- a saturated solution is one in which no more solute will dissolve in a specific amount of solvent at a specific temperature
- an unsaturated solution is one in which more solute can be dissolved in a specific solvent at the same specific temperature
- solubility chart (p. 20)
- using the particle theory, the attractive forces between the particles becomes balanced and no more particles of the solute can be attracted by the particles of the solvent

Beyond the Limit: Supersaturated Solutions

- a solution that contains more solute than would normally dissolve at a certain temperature is called a super-saturated solution.

Cleaning Up with Solvents

- Not all solute will dissolve in solvents. Insoluble means not able to be dissolved in a particular solvent.
- certain solvents are used for special circumstances because they will dissolve some solutes that water and other solvents cannot (rubbing alcohol is use to dissolve chlorophyll - grass stains, because the particles have strong attractions)

WHMIS Safety Symbols (refer to Safety Notes)


- Swedish dentists have developed a mixture that may replace the drill used for filling cavities. The mixture dissolves decayed dentine in teeth. It is a red mixture called Carisolv.
- Perchloroethethylene is the solvent used in 'dry' cleaning, even though it is a liquid