The Earth is made up of a large number of different substances elements, compounds mixtures We can classify elements compounds as pure substances. These are always HOMOGENEOUS. Mixtures are not pure substances and can be either homogeneous or HETEROGENEOUS. Pure substances have a fixed composition eg copper metal, sulfur, carbon dioxide (CO2), methane (CH4). Mixtures have variable composition and can also be separated into its components relatively easily. Eg. Alloys brass Cu 65 Zn 35 Elements are pure substances that cannot be broken down into any other substance. Compounds can be broken down, but this requires chemical means and is not as easy as separating mixtures. The Spheres of the Earth Atmosphere the cloak of gases that surrounds the earth or other planets, e.g. nitrogen, oxygen Hydrosphere all the water(s) on the Earths surface, including lakes, rivers etc. e.g. salt water Lithosphere the hard outer layer of the earth, including crust and upper mantle, e.g. ores (iron) Biosphere the part of the earth and its atmosphere in which living organisms exist or that is capable of supporting life, e.g. salt water Separating Mixtures Solids of different sizes sieving, sedimentation, magnetic separation, froth flotation, Solids liquids filtration, centrifugation Dissolved solids evaporation, crystallisation, freezing Solvents - separating funnel, distillation Two liquids distillation, separating funnel Jacaranda P.12 Identifying Pure Substances Colour some substances have a characteristic colour, eg CuSO4 blue. We can use this knowledge in a qualitative way to determine if a sample has impurities. Melting Boiling Point The mp bp of a substance is a good indicator of its purity. A pure substance will have a sharp melting point and its mp bp will not change after further attempts at purification. Impurities can lower or raise bp, but only lower mp. Density mass/volume pure substances have characteristic densities eg glass. Gravimetric Analysis This is a method used to determine the composition by mass of a substance. Mining determine the of a mineral in an ore deposit Quality control of products Determining the composition of a product made by a rival company Composition of a soil Pollutant in air or water Calculating composition A in ABC mass of A present x 100 Mass of total sample (ABC) Eg BaSO4 in Ore sample 3.61g of sample Mass of BaSO4 1.52g Mass of MgSO4 2.07g Total returned mass 3.59g BaSO4 1.52/3.61 x 100 42 MgSO4 100 42 58 2.07/3.61 x 100 58 Jacaranda P.21 Q3. A xenon is a gas at room temperatureB iridium is solid at room temperatureC caesium is solid at room temperatureD barium is solid at room temperature Q4. A - Density mass / volume 155.65/7.50 20.753g/cm3 B no C Pt D metal Physical Properties Uses of Elements Metals non-metals have differing properties. The properties of an element will determine what it is used for. Metals Metals are shiny in lustre, have high electrical and heat conductivity, very strong, malleable, ductile, high density and all solids at room temperature except mercury Eg Gold jewellery as its shiny Aluminium, Iron car parts as malleable Copper wire as it is ductile, a very good conductor Tungsten light bulb filaments due to v. High m.p Non-metals Non-metals are brittle, have low melting and boiling points, poor conductors of heat and electricity, dull lustre, low density Eg. Carbon (graphite) can conduct, so used as electrodes Carbon (diamond) used a tools Liquid N2(l) used in cooling Some elements have properties of both metals non-metals, these are classified as semi-metals or metalloids Eg silicon. Comparing Chemical Physical Changes Evidence of Chemical Reactions Evidence of chemical changes colour change temperature change light is given off precipitate formed gas is given off electrical potential created Different reaction classes include Endothermic reaction or process that is
