AP Chemistry Ch. 1 Section 1.9 Notes Classification of Matter Matter • has mass • occupies space • Exists in three states: solid, liquid, and gas • • • • • • Solid rigid shape fixed volume and shape very little volume change as temperature and pressure change properties determined by arrangement of particles only slightly compressible • • • • • • Liquid definite volume but no specific shape assumes the shape of its container fluid well-defined surface only slightly compressible • • • • • Gas no fixed volume or shape takes on the shape and volume of its container highly compressible volume varies according to temperature and pressure Classification of Matter • Matter can be classified into mixtures and pure substances. • • • • • • • • Pure Substances A pure substance is one with constant composition. The composition of a pure substance is always the same, regardless of its source. Example: all samples of water contain the same proportions by mass of hydrogen and oxygen. Pure substances contain compounds (combinations of elements) or free elements. Compounds Substance with a constant composition that can be broken down into elements by chemical processes. Example: sodium chloride (NaCl) commonly called table salt • Elements Elements are substances that cannot be broken down into simpler substances by chemical or physical means. Sodium, chlorine, iron, lead, copper, and aluminum are all common examples of elements. • • • • • Mixtures Most matter consists of mixtures of pure substances. Examples: wood, gasoline, wine, soil, and air Mixtures have variable composition. Two types: homogeneous and heterogeneous • • • • • • • Homogeneous Mixtures visibly indistinguishable parts same properties throughout also called solutions Examples: salt dissolved in water, brass, and air • • • • Heterogeneous Mixtures visibly distinguishable parts consists of two or more regions called phases that differ in properties Examples: pizza, chicken noodle soup, ice cubes in water • • Separation of Mixtures Mixtures can be separated into pure substances by physical methods. 1. Distillation: a process that depends on the differences in the volatility (how readily substances become gases) of the components. In simple distillation, a mixture is heated in a device and the most volatile component vaporizes (turns into gas) at the lowest temperature, and the vapor (gas) passes through a cooled tube (a condenser) where it condenses back into the liquid state. 2. Filtration: used when a mixture consists of a liquid and a solid. The mixture is poured onto a mesh, such as filter paper, which passes the liquid and leaves the solid behind. 3. Chromatography: general name applied to a series of methods that employ a system with two phases (states) of matter: a mobile phase and a stationary phase. The stationary phase is a solid, and the mobile phase is either a liquid or a gas. The separation occurs because the components of a mixture have different affinities for the two phases and thus move at different rates. A component with a high affinity for the mobile phase moves quickly. A component with a high affinity for the solid phase moves more slowly. • Paper Chromatography employs a strip of porous paper, such as filter paper, for the stationary phase. A line of the mixture to be separated is placed at one end of a sheet of porous paper (stationary phase). The paper is dipped into a liquid (the mobile phase). The paper acts as a wick to draw up the liquid. The component with the weakest attraction for the paper travels faster than the components that cling to the paper. Physical Properties and Changes • A physical property is one that can be observed without changing the chemical makeup of a substance. • Examples: mass, volume, boiling temperature, melting temperature, color, and conductivity. • Extensive properties: properties that depend on sample size. In other words, a property that changes when the size of the sample changes. • Examples: mass, volume, weight, and length. • Intensive properties: properties that are independent of sample size. In other words, a property that doesn’t change when you take away some of the sample. • Examples: color, electrical conductivity, density, hardness, melting point, and boiling point. • A physical change is a change in the form of a substance, not in its composition. • When water freezes or boils, its changes its state but remains water; it is still composed of H2O molecules. • Examples: melting, boiling, grinding, and pounding into sheets. Chemical Properties and Changes • A chemical property describes a chemical change (chemical reaction) that a substance undergoes. In other words, how a substance interacts with other substances. • Examples: flammability (the ability to catch on fire), toxicity (the ability to be poisonous), and oxidation (the ability to react with oxygen; which causes apple slices to turn brown and iron to rust). • A chemical change is one in which a given substance becomes a new substance or substances with different properties and different composition. • Examples: combustion (burning), cooking an egg, rusting of an iron pan, and mixing hydrochloric acid and sodium hydroxide to form water and a salt.