2 Physical Property – any characteristic of a material that can be observed or measured without changing the composition (makeup) of the substances in the material.These properties are used to identify a material or chose which material to use for a certain task.One must look at more than one physical property to make their decision.
3 Examples of physical properties ViscosityConductivityMalleabilityHardnessMelting and Boiling PointDensity
4 ViscosityViscosity – the tendency of a liquid to keep from flowing (its resistance to flowing)Thick liquids have a high viscosity.Thin, runny liquids have a low viscosity.Viscosity is usually decreased when the liquid is heated.
5 Conductivity Conductivity – material’s ability to allow heat to flow Metals conduct heat well…called conductors.If conducts heat well, usually conducts electricity well.Ouch!
6 MalleabilityMalleability – the ability of a solid to be hammered without shattering.Most metals are malleable.If not malleable, then we call substances brittle because it breaks when hammered (like ice).
7 Hardness Compare hardness by scratching. If a material can scratch another, then it is harder than the other material.Stainless steel can scratch copper. Thus, steel is harder than copper.A diamond is hardest known material.
8 Melting and Boiling Points Melting Point – temperature at which a substance changes from solid to liquidBoiling Point – temperature at which a substance changes from a liquid to a gas
9 Density Density – ratio of a substance’s mass to its volume Density = mass/VolumeMass – gVolume - mL or cm3 or ccDensity – g/mL or g/cm3
10 Densities Material Density (gm/ cm3) Water at 4 C 1.0000 Water at 20 C 0.998Gasoline0.70Magnesium1.7CopperGold19.3Ice at 0 C0.92AirHelium
11 Separating Materials via Physical Properties Filtration – separating materials based on the size of their particles (like straining spaghetti or tea)Distillation – process that separates the substances in a solution based upon boiling points.Distillation is done by heating a liquid until it boils, capturing and cooling the hot vapors, then collecting the condensed vapors. As a result the impurities (or unwanteds) are left behind in the 1st container.
12 Physical ChangePhysical change – occurs when some of the properties of a material change, but the substances in the material remain the same.Examples:Cutting hair (hair is still hair even though it looks different)Slicing a tomatoIroning a shirtFreezing water into iceSome physical changes are reversible, which means that you can take the substance back to the original.Ice melts and can become ice againWhen you cut hair off, you can’t put it back.