Grade 7 Science

Solutions

Solutions… a review

A homogeneous mixture ie. they appear as ONE substance

Examples: tap water, vinegar, gold jewelry, etc.

Solutions have 2 parts:

SoluteThe substance that dissolves (found in less amounts)

SolventThe substance in which the solute dissolves (found in the greatest amounts)

Dissolving...

To mix completely ie. the solute dissolves into the solvent.

Some substances are able to dissolve better than others.

The Particle Theory of Matter states that “there are attractive forces between the particles”.

In order to dissolve, the particles must be more strongly attracted to the particles of the solvent than to themselves. This means that the solute is soluble in that solvent.

If the particles of the solute are more attracted to their own particles than the solvent particles, dissolving does NOT occur. The solute is said to be insoluble in that solvent. (ie. Mechanical)

Soluble or Insoluble?

soluble

insoluble

Solvent or Not?

Some materials are good solvents for some solutes but not others. For example, oil is insoluble in water but soluble in gasoline.

States of Solutes and Solvents

AirSolute: oxygen, carbon dioxide, other gases

Solvent: nitrogen Gas

Gas

Soda

Solute: carbon dioxide

Solvent: water

Gas

Liquid

Vinegar

Solute: acetic acid

Solvent: water

Liquid

Liquid

Filtered Sea Water

Solute: Salt and other minerals

Solvent: Water

Solid

Liquid

Brass

Solute: zinc

Solvent: copper

Solid

Solid

**Alloy: Solutions made from two or more metals.

Rate of Dissolving…

Factors that affect the rate of dissolving include:

Size of the soluteTemperaturePressure

Size of Solute

The smaller the solute particles, the quicker they will dissolve

faster

Temperature

The higher the temperature, the more solute and the faster the solute will dissolvefaster

PressureGases are more soluble in liquids under higher pressure (see page 267)

Opened bottle decreases pressure and “bubbles” come out of solution

Separation TechniquesMechanical Sorting:Used to separate the parts of a mixture based on properties such as particle size.

Examples: floatation & magnetism

magnetism

floatation

Filtration:

A common way to separate solid particles from a mixture

The filters can have holes of varying sizes… small to microscopic.

Coffee filter

Oil filter

Furnace filter

Colander

Evaporation:

Change of state from a liquid to a gas.

Used to recover a solid solute from a solution.

Distillation:

Uses two changes of state: evaporation and condensation.

It allows you to recover BOTH the solute and solvent from a solution.

Evaporation

Condensation

Paper Chromatography:

Used to separate the colored substances in a mixture such as ink.

Used to separate the solvents in a mixture.

Separation Techniques in the Home:ColandersClothes dryersWindow screensCoffee percolatorsSalad spinnersAny others?

Distillation: A ReviewA method of separation that allows you to recover a single solute and a single solvent.

The mixture must boil so that the solvent can evaporate and then cooled so that it can condense back into a liquid.

Distillation Apparatus

Boil

Evaporation Condensati

on

Types of Distillations:

Simple DistillationSeparates a single

solute from its solvent.

Fractional DistillationSeparates a mixture of liquids based on their varying boiling points.