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Learn about the classification of matter into pure substances and mixtures, the properties and changes of matter, and the various methods used to separate mixtures. Explore solids, liquids, and gases, as well as homogeneous and heterogeneous mixtures.
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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 • visibly indistinguishable parts • same properties throughout • also called solutions • Examples: salt dissolved in water, brass, and air
Heterogeneous • 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 physicalmethods. • 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.
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.
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. The element mercury (top left) combines with the element iodine (top right) to form the compound mercuric iodide (bottom).
