Matter: Physical and Chemical Properties/Changes

Or BOTH!

Physical vs Chemical

When the change which has occurred does nothing to change the chemical composition of the substance, it is a physical change.

When the change which has occurred does change the chemical structure (bonds are formed, broken or both) then a chemical change has occurred.

A physical change does not change the chemical properties of the substance.

A chemical change does change the chemical properties of the substance.

Physical and Chemical

Physical Change

• Changing the shape, size, or phase of the material

• Warming it up and spreading out the particles.

• This change can be undone.

Chemical Change

• The chemical structure is not the same

• The properties of the material (solubility, flammability) have changed.

• This change cannot be undone.

Was It a Chemical Change?

We look for five things (and we want to observe at least two) to determine if it was a chemical change.

1. Heat is given off (exothermic) or absorbed (endothermic)

2. Fire

3. Light

4. Sound

5. Color Change (never enough by itself)

Properties

Properties are characteristics which are used to identify something.

In chemistry, we have physical properties and chemical properties.

Physical Properties

These are properties that describe the state of the physical system. They include: mass, length, solubility, density, boiling point, color, density, conductivity, hardness, strength

Physical Properties

Physical Properties come in two forms

a. One that depends upon the amount of material present (for example shape of sample)

b. And one that is independent of the amount (for example density)

• An intensive physical property is independent of the amount.

• An extensive physical property is dependent upon the amount.

A Chemical Property

It how the substance reacts when it forms a new substance.

Examples include: combustion, reactivity in water, flammability

Mixed

At times a property may have characteristics of both chemical and physical changes.

An example is pH.

pH is the measurement of the concentration of H+ ions in solution.

When an acid is added to water some or all of it will break into ions. Only if the pH is changed, it is truly a chemical change.

Uses of Chemical and Physical Properties

Separations

Separations

A mixture is two or more different chemical substances which are found in close proximity to one another.

To separate a mixture, we generally take advantage of physical properties (or mixed physical and chemical properties)/

Distillation

The physical property used to separate is boiling point. If the boiling point of the two substances are fairly separate, this is easy to do.

Needed materials: condenser, cold running water, heat source, and a collecting beaker.

Solubility

Solubility is taking advantage of the different substances that chemicals may or may not dissolve in.

Needed Materials: solvent or solvents, beaker

Chromatography is a method

that takes advantage of

solubility.

Magnetism

Some materials are magnetic and if they are the only magnetic material in the mixture, it can easily be removed.

Needed Materials: magnet and container

Density

Use different liquids to float or sink substances.

Materials needed: beaker or float pan and liquids

Filtering

Using particle size differences.

Needed Materials: filters, funnel, flasks, water for rinsing, and wash bottle

One step in treating municipal waste

Crystallization This takes advantage of two

properties: solubility and freezing point.

Need: one substance that is less soluble in the liquid with the higher freezing point

Needed Materials: liquid to dissolve, ice bath, beaker

Sublimation

This separation technique takes advantage of different boiling and sublimation temperatures.

Needed materials: heat source, watch glass, beaker, and ice