Transcript File
What is Chemistry? Why do we care? MATTER Chemistry is the study of matter. Matter: anything that has mass and takes up space Mass – the amount of matter in something Volume – the amount of space something occupies Mass vs Weight Mass is the amount of matter in a substance. It is fixed. Weight is in response to gravity. It changes. Compressibility Solids Liquids Gases NOT easily compressed Structure/ Arrangement of particles Particles are close together In a fixed (or rigid) arrangement Motion of Particles Shape Volume Move slowly Fixed Shape Fixed Volume NOT easily compressed Particles can flow and twist around each other Move faster than solids Takes the shape of its container Fixed Volume Easily compressed Particles are far apart – also flowing Move very quickly Takes the shape of its container Volume is equal to the volume of its container Phase Changes Liquid to gas = evaporation Liquid to solid = freezing Solid to gas = sublimation Gas to liquid = condensation Solid to liquid = melting Gas to solid = deposition Properties of Matter Physical Property – a characteristic of a substance that can change without changing the substance’s chemical composition Ex: color, texture, malleability, ductility, solubility, mass, volume, length, density, viscosity, phase changes Chemical Property – a property that changes the identity of a substance Ex: reactivity, toxicity, pH, conductivity, tarnishing, fermenting, oxidation, flammability Extensive vs Intensive Physical Properties Extensive Properties: Change when the size of a sample of matter changes. Can be used to quantify a substance. Intensive Properties: Properties that do not change with the sample size. Can be used to identify a substance. EXTENSIVE Mass Volume length INTENSIVE Color Odor Luster Malleability Hardness Ductility Conductivity Boiling/freezing/melting pt (temperature) density Physical and Chemical Changes Physical Change – a change in which the chemical composition of the substance is NOT altered Ex: cutting paper Chemical Change – a change in which the chemical composition of the substance is altered – a NEW substance is created Ex: iron rusting How do we know a chemical change occurred????? Some helpful hints -- Energy change Gas production Formation of a precipitate (what’s that??) Odor Color change What is the difference between physical and chemical changes? Physical change Chemical Change You can get it back Create a whole NEW substance to the original Burning (that wood substance All phase changes (melting, freezing, boiling, condensation, evaporation, sublimation) Size change Shape change that is now ashes will never turn back into wood!) Color change Produces gas/bubbles 1.Sublimation of iodine 2.Dissolving sugar into water 3. Crystallization of a supersaturated solution 4. Rusting Iron 5.Distillation of water and alcohol 6.Burning Candle 7. Boiling Water 8.Chewing Food 9. Digestion Of Food 10.Burning Wood 11.Evaporation of Water 12.Decomposition of water by electrolysis 13.Acid Rain acting on limestone 14. Metal salts burning in alcohol or combustion of alcohol 15.Tarnishing Silver 16.Melting Wax 17.Carbonic acid reacting with limestone 18. Sodium Reacting with Water 19. Melting Ice 20. Filtration of a sand and saltwater mixture Classification of Matter Substance?? Mixture?? Homogenous?? Heterogeneous?? Compound?? Element?? Separating Mixtures Some mixtures can be separated into their components by physical means. The following are common separation techniques. Separating Mixtures Distillation –A liquid is boiled to produce a vapor that is then condensed again to produce a liquid. The resulting liquid is pure. Ex: gasoline production from crude oil Filtration – A solid is separated from a liquid by passing the liquid through a filter which does not allow the solid to pass through. Ex: making coffee, water filter Separating Mixtures Solubility/Extraction – A substance dissolves preferentially into one medium over another when the media are mixed together and then separated again. Ex: olive oil dissolving flavors from herbs; water dissolving flavors from coffee beans. May be used with filtration. Chromatography – The parts of the mixture have different attractions for a mobile phase and stationary phase. Ex: separating the components of ink by placing a dot of ink on a piece of filter paper (stationary), and dipping the edge of the paper in water (mobile) Separating Mixtures Magnetism – Magnetic substances can be separated from nonmagnetic substances with a magnet. Ex: iron removed from crushed breakfast cereal with a magnet Evaporation – The most volatile (easy to evaporate) substance in a mixture can be lost by letting it evaporate, leaving behind the other substances. Ex: hard water residue on a sink