PHYSICAL AND CHEMICAL PROPERTIES Sections 2.2 and 2.3.
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Transcript of PHYSICAL AND CHEMICAL PROPERTIES Sections 2.2 and 2.3.
PHYSICAL AND CHEMICAL PROPERTIES
Sections 2.2 and 2.3
What is a Physical Property?
Any characteristic of a material that can be observed or measured without changing the composition of the substances in the material. Viscosity, conductivity, malleability,
harness, melting and boiling points, density, and temperature are just a few examples.
Viscosity
The tendency of a liquid to keep from flowing- its resistance to flowing.
The higher the viscosity of a liquid, the slower the liquid moves.
When a substance is heated, the viscosity of that substance lowers.
Conductivity
A material’s ability to allow heat to flow.
Materials with a high conductivity are called conductors.
Malleability
The ability of a solid (metal) to be shaped without breaking.
Hardness, Melting & Boiling Points
To test hardness of material, you see which material can scratch the other.
Melting Point: The temperature at which a substance changes from a solid to liquid.
Boiling Point: The temperature at which a substance boils.
Density
Density is a ratio of the mass of a substance to its volume d=m/v
Objects made out of the same material have the same density.
Density can be used to test the purity of a substance.
Using Properties to Separate Mixtures
Filtration: A process that separates materials based on the size of their particles by using a strainer or filter.
Distillation: A process that separates the substance in a solution based on their boiling points.
Physical Changes
Occurs When some of the properties of a material change, but the substances in the material remain the same.
Some physical changes can be reversed. Freezing, melting, then
freezing water again
What is a Chemical Property?
Any ability to produce a change in the composition of matter.
Can only be observed when the substances in a sample of matter are changing into different substances.
Examples
Flammability The material’s
ability to burn in the presence of oxygen.
Lighting a candle
Reactivity How readily a
substance combines chemically with another substance.
Oxygen reacts easily with most elements. When oxygen reacts with iron and water rust forms.
Flammability Reactivity
Recognizing a Chemical Change
A chemical change occurs when a substance reacts and forms one or more new substances.
Three common types of evidence: Change of Color Production of Gas Formation of a Precipitate
Any solid that forms and separates from a liquid mixture.
Is it Chemical or Physical?
Don’t be fooled! A color change or production of gas doesn’t
always mean that a chemical change has taken place.
Ask yourself this: Are different substances present after the
change takes place? If you answer “no” then it’s a physical change If you answer “yes then it’s a chemical change