Lecture 4Lecture 4
•Classification ofMixtures
•Solutions
•Solubility
•Water Treatment
MixturesMixtures
•Mixture: a combination oftwo or more substances inwhich each substanceretains its own properties.
–Most materials are mixtures.
Compound
Element
Mixture
•The formation of a mixture is considered aphysical change.
–No new substance is formed – mixtures do not formfrom chemically bonded atoms.
–Each substance retains its chemical identity.
–Can be separated by physical means.
Separating MixturesSeparating Mixtures
•Filtration: use of a filter inthe separation of a solid-liquid mixture.
–Commonly part of the water-purification process.
Separating MixturesSeparating Mixtures
•Distillation:
–Takes advantage of differences in boiling or meltingpoints (ex. water boils at 100°C, salt melts at 800°C).
–Heat seawater to 100°C and water becomes a vaporwhile salt is left behind.
–Water vapor is collected, cooled, and condensed intopure liquid water.
Classification of MatterClassification of Matter
•Pure: consists of only a single element ora single compound.
•Impure: a mixture containing 2 or moreelements and compounds.
Classification of MatterClassification of Matter
•Heterogeneous Mixture: different componentsof mixture are distinguishable.
Classification of MatterClassification of Matter
•Homogeneous Mixture: mixture with the samecomposition throughout – individual componentsare not visible.
Classification of MatterClassification of Matter
•Solution: a homogeneous mixture in which allcomponents are in the same phase.
–Examples: salt water, metal alloys, air
•Suspension: a homogeneous mixture in whichthe different components are in different phases.
–Examples: milk, fog, blood
Ruby = a solid solutionof aluminum oxide andred chromiumcompounds.
Solutions can be solids, liquids, or gases.
The path of light made visible by a suspension.
SolutionsSolutions
•Solvent: (dissolves other materials) componentof a solution present in the greatest quantity.
–Example: water
•Solute: (gets dissolved) present in lesseramounts.
–Example: salt
•Saturated Solution: a solution in which no more solutecan be dissolved.
•Unsaturated Solution: a solution that has not reachedthe limit of solute that can be dissolved.
SolutionsSolutions
•Concentration: the amount of solutedissolved per amount of solution.
= amount of solute / amount solution
•Example: a solution of sugar-water has 2gof sucrose per liter of solution.
SolubilitySolubility
•Solubility: the ability of a solute to dissolvein a solvent.
•Solubility depends on:
–electrical attractions between solute and solventparticles.
–attraction of solute particles for one another.
–attraction of solvent particles for one another.
•Sucrose molecules held together by multiple stronghydrogen bonds.
•Multiple H2O molecules needed to pull sucrosemolecules away from one another.
•Places a limit on how much sucrose can be dissolved.
SolubilitySolubility
•Infinitely soluble:
–When attractions between solute moleculesare similar to attractions between solventmolecules.
–Examples: water and ethanol, gases inatmosphere.
Infinitely soluble: Can be mixed in any proportions.
•O2 and Water:
–Only 0.004 g of O2 can
dissolve in 100 mL of water.
–Relatively weak attractions between O2 (nonpolar)and H2O (polar).
–Water molecules have stronger attractions for oneanother.
SolubilitySolubility
•Insoluble: a material that does notdissolve in a specific solvent.
–Example: sand and glass are insoluble inwater.
–However, sand and glass are soluble in HFacid.
SolubilitySolubility
•Solubility changes with temperature.
•Many water-soluble solids dissolve more easilyin hot water than in cold water.
–Water molecules move more rapidly.
–More violent collisions with solute molecules.
–Collisions disrupt bonds between solute molecules.
•Some water-soluble solids become lesssoluble as water temperature increases.
–Calcium Carbonate (CaCO3) precipitates outof solution as a solid at higher temperatures.
SolubilitySolubility
•Precipitate: solid residue formed whenthe solubility of a solid substancedecreases in a solution.
•Caused by changes in:
–temperature.
–concentration.
SolubilitySolubility
•The solubility of gases in liquids decreaseswith increasing temperature.
–gas molecules are ejected by the increasinglyenergetic solvent molecules.
–Example: carbonated beverages go flat fasterwhen warm.
SolubilitySolubility
•Solubility of a gas also depends on thepressure of the gas above the liquid.
–Higher pressures allow for more gas to bedissolved - more gases forced into solution.
SolubilitySolubility
•When a gas solutecomes out of solutionit forms bubbles –“fizzing”.
•Gas molecules collecttogether formingbubbles that rise tothe surface due tolower density.
Water PurificationWater Purification
•One of the most important global issues is thesupply of clean freshwater for a growingpopulation and economy.•One of the most important global issues is thesupply of clean freshwater for a growingpopulation and economy.
Water PurificationWater Purification
•Removal of solids (dirt, bacteria) insuspension.
Water PurificationWater Purification
•Filter water throughsand and gravel.
•Odor and flavorimproved by aeratingthe water – some airdissolved into water.
Water PurificationWater Purification
•Disinfected with Cl2 or sometimes O3.
•Many diseases are contracted by drinkingcontaminated water.
–Example: in the early 1990’s, when the Perugovernment stopped the chlorination of itswater supply, there were 1.3 million newcases of cholera and 13,000 deaths.
Disinfection by exposure to UV radiation.Disinfection by exposure to UV radiation.
Disinfection of water by exposure to solar UV radiation.
DesalinationDesalination
•Greatest water reserves contain seawater andbrackish (moderately salty) water.
•Two processes for removing salts:
–Distillation
–Reverse Osmosis
•Also important methods for removingcontaminants such as fertilizers and pesticides.
DesalinationDesalination
•Distillation:•Distillation:
–Very energy-intensive because of water’s highheat of vaporization and high heat capacity.–Very energy-intensive because of water’s highheat of vaporization and high heat capacity.
–Many distillation plants require the burning oflarge quantities of fossil fuels.–Many distillation plants require the burning oflarge quantities of fossil fuels.
DesalinationDesalination
•Solar Distillers: require about 1 m2surface area to produce 4 L of fresh waterper day.
DesalinationDesalination
•Osmosis: the netflow of water across asemi-permeablemembrane into amore concentratedsolution.
Reverse Osmosis: water is forced across asemipermeable membrane into a less concentrate solution.
Modern reverse osmosis facilities can produce millionsof gallons of freshwater per day.
