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Matter: Pure Substances and Wixtures Matter can be broadly categorized into two groups: pure substances and mixtures. Most matter encountered in daily life exists as mixtures of two or more pure components. I. Pure Substances 4 pure substance in chemistry is defined as_a form of matter that has a constant and definite composition and_consistent properties throughout any given sample. For a scientist, "pure. means that all the constituent particles of that substance are chemically identical. It consists of a single type of particle. Regardless of its source, a pure substance will always exhibit the same characteristic properties. For example, ice, water and water vapor_are chemically the_same pure substance, walter (H20), even though their physical properties differ Pure substances can he further classified hased_on their chemical composition into elements or compounds, * A. Elements © An element isa basic form of matter that cannot he broken down into simpler substances hy chemical_reactions, Robert Boyle first_used the term_in 1661, and Antoine Laurent Lavoisier provided its experimentally useful_definition, © There are over 100 known elements, with ninety-two occurring naturally and_the rest heing man-made. o Most elements are solid at room temperature; eleven are gaseous, and_two (mercury and bromine) are. liquid. Callium_and_cesium become liquid slightly above room temperature (303 K). © Elements are generally categorized into: = Metals: These typically possess lustre (shine), are silvery-grey or golden-yellow, conduct heat and electricity well, are ductile (can he drawn into wires), malleable (can be hammered into thin sheets), and_sonorous (produce a_ringing sound when struck), Examples include gold, silver coppen_ iron, sodium, and potassium. = WNon-metals: These display a variety of colours, are poor conductors of heat and electricity, and_lack lustre, sonority, or malleabilty, Examples include hydrogen, oxygen, iodine, carbon (coal, coke), bromine, and chlorine. = WMetalloids: These elements exhibit properties that_are_intermediate between those of metals and_non-metals. Examples include_horon, silicon, and germanium. 9 Examples of items classified as elements include gold, iron, helium, and selenium. oe) Compounds of compound is_a_substance composed of two or more elements that are chemically combined with one another ina fixed proportion, © The formation of a compound from elements involves a chemical change (chemical reaction), of key characteristic of a compound is that_it_has totally different properties compared to the elements that combine to form. it. For instance, sodium (a soft, shiny metal) and_chlorine (a pungent green gas) © There is homogeneity at the particle level, meaning particles are evenly distributed. A homogeneous mixture consists of a single phase. 9 Examples include salt dissolved in water sugar dissolved in water lemonade, soda water and filtered tea. © Solutions are not limited to liquids; they can also he solid solutions (like alloys such as brass, which is a mixture of zinc and copper) and gaseous solutions (like ain a mixlure_of oxygen and nitrogen). Although air has_a_unitorm composition and_consistent properties, in chemistry, it is considered a homogeneous mixture rather than_a pure substance because its components can he separated hy physical means like distillation. © AA solution consists of a solvent and a solute. The solvent is the component that dissolves the other, usually present ina larger amount, The solute is the component dissolved_in_the solvent, usually in_a_lesser quantity, For example, ina sugar-waler solution, sugar_is the solute and water is the solvent. SF Properties of _a Solution: " Tt isa homogeneous mixture, = The particles are extremely small, less than_|_nanometer (10-° meter) in diameter, and cannot he seen with the naked eve, ® Que to their small size, they do_not_scaller a beam of light passing through the solution, so_the path of light is_nol_visible (ie, they do_not exhibit the Tyndall effec’ ). = The solute parlicles cannot he separated hy filtration. = The solute particles do not settle down when left undisturbed, indicating that a solution is stable. © Concentration of a Solution: This refers to the amount (mass or volume) of solute present in_a_given amount (mass or volume) of solution. ® Solutions can he described as dilute, concentrated, or saturated. These are comparative terms. = A saturated solution is one that has dissolved the maximum amount of solute _it is capable of dissolving ata particular temperature. No more solute can he dissolved in a saturated solution at that temperature. . Solubility is the amount of solute present in_a saturated solution at a given temperature. Oifferent substances have different solubilities in a given solvent at the same temperature. = An unsaturated solution contains less solute than the saturation level_at a_given temperature, = Concentration can he expressed as: * Mass hy mass percentage: (Mass of solute _/ Mass of solution) x 100. ° Mass hy volume percentage: (Mass of solute | Volume of solution) x 100. : Uolume hy volume percentage: (Volume of solule / Volume of solution) x_100. S B Heterogeneous Mixtures of heterogeneous mixlure_is_a_mixture_in_which the composition is_not © The solute parlicles settle down when left undisturbed, indicating that a suspension is unstable. When the particles sellle, the Suspension breaks and_no longer scatters light. © They can he separated from the mixture by Filtration. = 2. Colloidal Solutions (Colloids): * Colloids are mixtures that appear homogeneous due to the uniform spread of particles and their relatively smaller size compared to suspensions, but they are actually heterogeneous mixtures. ° Examples include milk, ink, fog, clouds, mist, smoke, automobile exhaust, shaving cream, Face cream, milk of magnesia, mud, foam, rubber sponge, pumice, jelly, cheese, hutlen coloured gemstones, and milky glass, ° Properties of a Colloid: ° Tt is a heterogeneous mixture. © The size of colloidal particles is too small to he individually seen_with the naked eue, © These particles can easily scatter a heam_of visible light, making its path visible. This phenomenon is called the Tyndall effect, named_after its discoverer The Tyndall effect can be observed when a light beam enters a dusty room through a_small_hole or when sunlight passes through a dense forest canopy. © They do_not settle down when_left undisturbed, indicating that_a_colloid is quite stable. © They cannot he separaled hy simple Filtration; a special technique called centrifugation can he used. ° Components of a Colloidal Solution: A colloidal solution has a dispersed phase and a dispersion medium. ° The dispersed phase refers to the solute-like component or the dispersed particles in_a colloid. © The dispersion medium is the component in which the dispersed phase is suspended. * Colloids are classified hased on the physical state (solid, liquid, or gas) of both the dispersed phase and_the dispersing medium. II Physical and Chemical Changes Matter can undergo physical or chemical changes. 4 Physical Changes ° Ina physical change, properties such_as coloun hardness, rigidity, fluidity, density, melting point, and boiling point can he observed ana specitied, ° These changes occur_without_a change in the chemical composition or the chemical nature of the substance. Ihe substances involved retain their original chemical_characleristics, ° Tnterconversion_of states (og, ice melting to walen waler hoiling to water vapor) is_an example of_a physical change because the chemical identity of water remains the same (H,0). © Examples include cutting of trees, melting of butter ina pan, boiling of water to Form steam, dissolving common. salt_in water, and making a Feuit_salad_with raw fruits. 
