Physical Properties and Changes

Physical Properties Can be observed with the senses and can be determined without changing the substance. Examples of physical properties are color, shape, mass, length, and odor.

Physical Properties Viscosity- A liquids resistance not to flow o The greater the viscosity the slower the liquid moves o Viscosity decreases as a substance is heated

Physical Properties Conductivity-A materials ability to allow heat to flow o Materials with a high conductivity include metals. o Wood is a poor conductor.

Physical Properties Malleability- The ability of a solid to be hammered without shattering o Gold is used in jewelry because of its malleability. o Glass is not malleable and will shatter when hammered because it is brittle.

Physical Properties Hardness- The ability of a material to be scratched or to scratch another surface o Mohs Scale of Hardness A kitchen knife can scratch a copper sheet because stainless steel is harder than copper. The material used to sharpen the knife blade must be harder than stainless steel. Diamond is the hardest known material.

Physical Properties Melting Point- The temperature at which a substance changes from a solid to a liquid Boiling Point- The temperature at which a substance changes from a liquid to a gas

Physical Properties Density- Mass/Volume. Can be used to test pureness of a substance.

Using Properties to Identify Materials A material can be identified by its properties. Decide which properties to test. Do tests on a sample of the unknown material. Compare the results with the data reported for known materials.

Using Properties to Choose Materials Properties determine which materials are chosen for which uses. For example, shoelaces must be flexible, that is they must be able to bend without breaking. They must also be durable, that is, they must be able to withstand repeated use.

Separating Mixtures Filtration- separates materials based on the size of their particles

Separating Mixtures Distillation- separates materials based on their boiling points

Physical Changes When properties of a material change, but the composition of the material does not change. Melting, boiling, freezing, condensing are used to describe reversible physical changes Breaking, splitting, cutting, and crushing are words that are used to describe irreversible physical changes

Chemical Properties and Changes

Chemical Properties Chemical Property: the ability to produce a change in the composition of matter Chemical properties can be observed only when the substances in a sample of matter are changing into different substances.

Chemical Properties Examples Flammability – ability to burn in presence of O 2

Chemical Properties Reactivity – how readily a substance combines chemically with other substances. o Oxygen reacts readily with iron and water to form rust

Chemical Properties Nitrogen has many uses that depend on its low reactivity. Researchers in Japan pump nitrogen gas into the steel tanks that hold seawater in ships. The nitrogen displaces the oxygen dissolved in the water and prevents rusting.

Chemical Change Produces matter with a different composition then the original matter Evidence for chemical changes: o Color change o Production of gas o Formation of precipitate (a solid that forms and separates from a liquid mixture)

Color Change The color change in a banana peel is caused by chemical changes that are taking place in the cells of the banana. A chemical change occurs when a substance reacts and forms one or more new substances.

Production of Gas When you mix vinegar with baking soda, bubbles of carbon dioxide form immediately. A similar chemical change happens when you use baking powder as an ingredient in a cake recipe. Bubble of carbon dioxide expand and cause the cake to rise.

Formation of a Precipiate Any solid that forms and separates from a liquid mixture is called a precipitate. When an acid is added to milk, proteins in the milk undergo a chemical change that causes them to stick together in clumps and form a precipitate– cottage cheese.

Chemical or Physical If the composition of the matter changes, it is a chemical change. If the composition of the matter remains the same, it is a physical change.

Property or Change Properties can be differentiated from changes in that properties are adjectives and changes are verbs. For example, fireworks have the ability to explode. That ability is a property. But if the fireworks actually explode, then it is considered a change