Section 2–2: Physical Properties Coach Kelsoe Physical Science Pages 45–51

Objectives Describe physical properties of matter. Identify substances based on their physical properties. Describe how properties are used to choose materials. Describe methods used to separate mixtures. Describe evidence that indicates a physical change is taking place.

Examples of Physical Properties A physical property is any characteristic of a material that can be observed or measured without changing the composition of the substances in the material. Viscosity, conductivity, malleability, hardness, melting point, boiling point, and density are examples of physical properties.

Viscosity Then tendency of a liquid to keep from flowing (or the resistance to flowing) is called its viscosity. Honey has a high viscosity, while water has a low viscosity. The viscosity of a liquid usually decreases when it is heated. We talk about viscosity a lot when talking about motor oil.

Conductivity A material’s ability to allow heat to flow is called conductivity. Materials that have a high conductivity, such as metals, are called conductors. If a material is a good conductor of heat, it is usually also a good conductor of electricity.

Malleability Malleability is the ability of a solid to be hammered without shattering. Most metals are malleable. The opposite of malleability is brittleness. Gold is malleable. Glass is brittle.

Hardness One way to compare the hardness of two materials is to see which of the materials can scratch the other. When you sharpen a blade, the sharpener must be harder than the blade itself. Diamond is the hardest known material.

Melting and Boiling Points The temperature at which a substance changes from a solid to a liquid is its melting point. The temperature at which a substance boils is its boiling point. Melting and Boiling Points of Some Substances SubstanceMelting PointBoiling Point Hydrogen ° C ° C Nitrogen ° C ° C Ammonia-77.7 ° C-33.3 ° C Octane-56.8 ° C125.6 ° C Water0°C0°C100.0 ° C

Density Density can be used to test the purity of a substance. It is the ratio of the mass of a substance to its volume. Density is used to test the purity of methanol, which is used in some racing motorcycles.

Using Physical Properties People use data about physical properties to solve many different types of problems. Physical properties are used to identify a material, to choose a material for a specific purpose, or to separate the substances in a mixture.

Using Properties to Separate Mixtures Some properties can be used to separate mixtures. There are many ways to separate a mixture, but two of the most common ways are by filtration and distillation. – Filtration is a process that separates materials based on the size of their particles. – Distillation is a process that separates the substances in a solution based on their boiling points.

Recognizing Physical Changes A physical change occurs when some of the properties of a material change, but the substances in the material remain the same. Melting butter, crumpling paper, dying hair, slicing apples, or chopping wood are examples of physical changes. Some physical changes can be reversed, while others can not.

Vocabulary Physical property Viscosity Conductivity Malleability Melting point Boiling point Filtration Distillation Physical change