Presentation on theme: "“Everything around us is made up of chemicals, including ourselves"— Presentation transcript:
1 “Everything around us is made up of chemicals, including ourselves “Everything around us is made up of chemicals, including ourselves. Some things are made up of a single chemical, or substance. Orange juice, however, contains different kinds of molecules and is a mixture of substances. Vinegar is a solution with water acting as a solvent in which the other substances are dissolved. These substances can be separated physically from one another. Most foods are mixtures. Salad dressing is a mixture, called an emulsion, containing oil and vinegar. They do not mix properly, but separate out into the lighter oily layer and the heavier water layer containing the vinegar. Other kinds of mixtures may be solids, like coins, or gases, like the air around us. Toothpaste is a mixture called a suspension, in which fine particles are suspended in a liquid, and they do not dissolve. It is often necessary for chemist to separate out the different chemicals to find out what they are.”Eyewitness Science “Chemistry” , Dr. Ann Newmark, DK Publishing, Inc., 1993, pg 14Solutions
2 Definitions Solution - homogeneous mixture Solute - substance being dissolvedR O M I S OThe Boom tells this story to his Chemistry students when they are studying types of mixtures and solutions. After this they will never forget the difference between homogeneous and heterogeneous mixtures.Romiso was a very obese and somewhat disgusting individual. He smoked. and he stank like a smoker. Furthermore he usually had tobacco juice dripping down his chin. His matches seldom ignited because they were soaked in sweat. He was always begging others for food, matches or cigarettes.In general... YUK!Bie had an antique Chevrolet sedan with a large square front windshield. At Abe Lincoln High, many students would lunch in their cars.On this occasion, Bie, Newell, and Trow were in the front seat. Romiso occupied the entire back seat. Romiso was attacking an egg sandwich.Then Romiso sneezed!The front windshield bore three silhouettes. It was easy to tell that egg sandwiches are heterogeneous. There were bits of egg white, egg yolks, lettuce, mayonnaise, and a multitude of other ingredients all over the windows. And it was a non-uniform distribution. Heterogeneous!One day a group of us high school kids were at the end of the Santa Cruz Wharf. Romiso was unfortunately present. He was big enough to be omnipresent."Give me cookies! Come on, I need cookies for this!""Forget it, Romiso. Get your own cookies.""You guys need to see this. I'm the world champion. Come on give me cookies. No kidding, I'm the world's champion.""OK, you slob, here," said Newell.Romiso dug deeply into the cookie bag. Mutilated pieces were stuffed into his mouth. Crumbs were all over his sweaty shirt."Cmonmnonovllertodaraaaal," he mumbled through his overstuffed oral cavern."What are you trying to say, you pig?" demanded Trow."Aysaaaidcommmmovertodadraaaal.""He wants us to come over to the rail," said Walt."OK, what is it going to be this time?" we wondered.Romiso leaned over the railing and proceeded to expectorate. The viscous fluid slowly emanated from his mouth and slowly lowered itself toward the ocean below. It was incredible. It went five meters before it stopped, hovered, and then it returned into Romiso's mouth.Three times he accomplished this feat before it broke free."I call this the yo yo spit," he informed us after it was over.All of this time one could observe the bits of cookie within the pendant effluent.Definitely a heterogeneous and viscous situation with high surface tension.So, students, you'll never forget the meaning of heterogeneous!Solvent - present in greater amount
3 Solutions What the solute and the solvent are determines whether a substance will dissolve.how much will dissolve.A substance dissolves faster if it is stirred orshaken.The particles are made smaller.The temperature is increased.Why?StirringIn order to dissolve the solvent molecules must touch the solute.Solvent molecules hold on to and surround the soluteStirring moves fresh solvent next to the solute.Dissolves fasterParticle SizeThe solvent touches the surface of the solute.Smaller pieces increase the amount of surface of the solute.Solvent and solute touch each other more oftenSmaller particles dissolve fasterTemperatureHigher temperature makes the molecules of the solvent move around faster and contact the solute harder and more often.More pieces are broken offSpeeds up dissolving.Usually increases the amount of solid that will dissolve.
4 Factors Affecting the Rate of Dissolution As To , rate1. temperatureAs size , rate2. particle size∆ Surface AreaMore mixing, rateFormation of a solution from a solute and a solvent is a physical process, not a chemical one.Both solute and solvent can be recovered in chemically unchanged form using appropriate separation methods.Dissolution of a solute in a solvent to form a solution does not involve a chemical transformation.Substances that form a single homogeneous phase in all proportions are said to be completely miscible in one another.If two substances are essentially insoluble in each other, they are immiscible.3. Agitation4. nature of solvent or solute
5 Solution = Solute + Solvent Solute - gets dissolvedSolvent - does the dissolvingAqueous (water)Tincture (alcohol)Amalgam (mercury)OrganicPolarNon-polarDental fillingSolutions are always homogeneous – evenly mixed.Solutions– In all solutions, whether gaseous, liquid, or solid, the substance present in the greatest amount is the solvent, and the substance or substances present in lesser amounts are the solute(s).– Solute does not have to be in the same physical state as the solvent but the physical state of the solvent determines the state of the solution.– If solute and solvent combine to give a homogeneous solution, solute is said to be soluble in the solvent.The difference between hydrophilic and hydrophobic substances has substantial consequences in biological systems.– Vitamins can be classified as either fat soluble or water soluble.1. Fat-soluble vitamins (Vitamin A) are nonpolar, hydrophobic molecules and tend to be absorbed into fatty tissues and stored there.2. Water-soluble vitamins (Vitamin C) are polar, hydrophilic molecules that circulate in the blood and intracellular fluids and are excreted from the body and must be replenished in the daily diet.AmalgamAmalgam is a commonly used dental filling that has been used for over 150 years. It is a mixture of mercury with at least one other metal. Currently dental amalgams are composed of about 40% mercury, and 60% powder where the powder is made up of Silver (~65%), Tin (~29%), copper (~10%) and zinc (~2%). Amalgam has many advantages over other restorative material, such as low cost, strength, durability and bacteriostatic effects. Its main disadvantage is poor esthetics on anterior teeth. There have been some concerns over the years about the detrimental health effects from the low levels of mercury released from amalgam, however there is no scientific evidence to support any detrimental effect.Nightmare on White StreetChem Matters, December 1996
6 Classes of Solutions aqueous solution: solvent = water water = “the universal solvent”amalgam:solvent = Hge.g., dental amalgamtincture:solvent = alcohole.g., tincture of iodine (for cuts)organic solution:solvent contains carbone.g., gasoline, benzene, toluene, hexane
7 Solution Definitions solution: a homogeneous mixture -- evenly mixed at the particle level-- e.g., salt wateralloy:a solid solution of metals-- e.g., bronze = Cu + Sn; brass = Cu + Znsolvent: the substance that dissolves the solutewatersaltSolutions– A homogeneous mixture in which substances present in lesser amounts, called solutes, are dispersed uniformly throughout the substance in the greater amount, the solvent– Aqueous solution — a solution in which the solvent is water– Nonaqueous solution — any substance other than water is the solvent– Water is essential for life and makes up about 70% of the mass of the human body.– Many of the chemical reactions that are essential for life depend on the interaction of water molecules with dissolved compounds.soluble:“will dissolve in”miscible:refers to two gases or two liquids that forma solution; more specific than “soluble”-- e.g., food coloring and water
8 Types of Solutions Solute Solvent Solution Gaseous Solutions liquidair (nitrogen, oxygen, argon gases)humid air (water vapor in air)Liquid Solutionssolidcarbonated drinks (CO2 in water)vinegar (CH3COOH in water)salt water (NaCl in water)Solid Solutionsdental amalgam (Hg in Ag)sterling silver (Cu in Ag)Solutions are not limited to gases and liquids; solid solutions also exist.• Amalgams, which are usually solids, are solutions of metals in liquid mercury.• Network solids are insoluble in all solvents with which they do not react chemically; covalent bonds that hold the network together are too strong to be broken and are much stronger than any combination of intermolecular interactions that might occur in solution.• Most metals are insoluble in all solvents but do react with solutions such as aqueous acid or base to produce a solution; in these cases the metal undergoes a chemical transformation that cannot be reversed by removing the solvent.Charles H.Corwin, Introductory Chemistry 2005, page 369
9 An alloy is a homogeneous mixture of metals. Brass = Copper + ZincSolid brasshomogeneous mixtureSolid BrassConsumer TipPay attention to labels when purchasing brass. Brass is sold with the label ‘Brass’ or ‘Solid Brass’.‘Brass’ means brass coated – the object is not ‘solid brass’. It is likely inexpensive, cheap zinc in the center and has only a thin coating of brass on the outside.Toilet bowl seat screws are often sold as ‘brass’ ($1.29) or ‘solid brass’ ($1.99).Pay more, the ‘brass’ screw may snap off as zinc is a brittle metal under stress.‘Solid brass’ is stronger and the better value.CopperZinc
10 Brass Plated Brass = Copper + Zinc Brass plated heterogeneous mixture Only brass on outsideBrass PlatedCopperZinc
11 Hardened Steel Steel Iron Carbon Carbon is added to steel to make it harder. The addition of too much carbon makes steel very strong, but brittle. A bridge made this way would not sag when stressed, but would snap when too much pressure was applied. Engineers figure the optimal amount of carbon to add to make steel strong, but not too brittle.Look for link: SteelSteelIronCarbon
12 Gold 24 karat gold 18 karat gold 14 karat gold 24/24 atoms Au CopperSilver24 karat gold karat gold karat goldPure gold (24 karat) is too soft (malleable) for use in jewelry. An alloy is made with copper or silver to make the gold harder and more durable. 14 karat gold means if you take 24 atoms out of the sample 14 will be gold atoms and the remaining 10 atoms another metal.Many years ago, coins were made from pure silver and pure gold. Dishonest people would shave off the edges of the coins to steal a small amount of silver or gold. Ridges were added to coins to stop people from shaving the coins.Emphasize that alloys are solutions or mixtures of metals. An alloy’s characteristics differ from those of the metals that compose it.How are the silver atoms arranged in the14-karat gold?(They are evenly dispersed among the gold atoms.)If you were to melt the ring, how would the silver atoms be arranged in the solution?(They would be evenly dispersed.)Can an alloy be composed of more than two different metals?(yes)24/24 atoms Au18/24 atoms Au14/24 atoms Au
13 Non-Solution Definitions insoluble:“will NOT dissolve in”e.g., sand and waterimmiscible:refers to two gases or two liquids that will NOT form a solutione.g., water and oilsuspension:appears uniform while being stirred, but settles over time
14 Solubility Experiment 1: Add 1 drop of red food coloring A B A B BeforeWaterHOTAFTERCOLDA BMiscible – “mixable”two gases or two liquidsthat mix evenlyWaterCOLDWaterHOTYou should observe that temperature effects the rate of solution. As the temperature of the liquid solvent increases, the molecules move faster, and the food coloring dissolves more quickly.A B
15 Solubility Experiment 2: Add oil to water and shake T0 sec T30 sec AFTERBeforeImmiscible – “does not mix”two liquids or two gasesthat DO NOT MIXOilYou should observe that for solutions to mix they must be chemically similar. Polar and polar molecules will mix, non-polar and non-polar molecules will mix, but polar and non-polar molecules will not mix. The reasons for this will be explained later.Remember, ‘like dissolves like’. polar dissolves polarnon-polar dissolves non-polarWaterWaterT0 secT30 sec
16 Muddy Water: Dissolved Solids Experiment 3:Add soil to water, shake well, and allow to settleAFTERBeforeMuddyWaterDissolved solids can be calculatedas a percentage:v/v (volume/volume)w/v (weight/volume)w/w (weight/weight)Water5% v/v soil in water5 mL solid / 95 mL waterT1 min T5 min5 mL / 100 mL = 5%
17 Muddy Water: Flocculation Al2(SO4) Ca(OH)2 2 Al(OH) CaSO4Experiment 4:Add soil to water, shake well, and allow to settleAFTERAFTERBeforeBeforeMuddyWaterMuddyWaterWaterWaterDemonstrate flocculation – a method used to settle out solids from waste water.Two 50-mL graduated cylinderspea-sized ball of moist mud (clay or silty-clay) in eachFill ¾ full of tap waterCover top with thumb and shake until well-mixedGo on with something else for minutes (like stoichiometry calculations dealing with Al2(SO4) Ca(OH)2 2 Al(OH) CaSO4ADD POWDERED MIXTURE OF ~3 g Al2(SO4) H2O g Ca(OH)2 to one graduated cylinder and shake [DO NOT MIX AHEAD OF TIME]Flocculation begins within one minute and is complete in 4 – 5 minutes!T1 min T15 minT1 min T5 minNO Flocculation materialWITH Flocculation material
18 Flocculation Mechanism Flocs by PAC stick to micro-sand by means of polymer. ItemsRemovalRatio (%)BOD75CODSS90
19 CentrifugationSpin sample very rapidly: denser materials go to bottom (outside)Separate blood into serum and plasmaSerum (clear)Plasma (contains red blood cells ‘RBCs’)Check for anemia (lack of iron)AFTERBeforeRBC’sSerumBloodWhen you donate blood, the phlebotomist will check for anemia before drawing your blood. A small amount of blood will be taken from your fingertip into a thin glass tube. The blood may be placed in a centrifuge as described above to check for sufficient amounts of red blood cells. An alternate method is to drop the blood in a solution of copper sulfate. If the blood contains enough RBC’s the blood drop will sink to the bottom of the container, if it is not dense enough (lacks adequate number of RBC’s), the blood will float and you will not be allowed to donate blood.AB C
22 Making solutionsIn order to dissolve - the solvent molecules must come in contact with the solute.Stirring moves fresh solvent next to the solute.The solvent touches the surface of the solute.Smaller pieces increase the amount of surface of the solute.When a solute dissolves, its individual atoms, molecules, or ions interact with the solvent, become solvated, and are able to diffuse independently throughout the solution.• If the molecule or ion collides with the surface of a particle of the undissolved solute, it may adhere to the particle in a process called crystallization (formation of a solid with a well-defined crystalline structure).• Dissolution and crystallization continue as long as excess solid is present, resulting in a dynamic equilibrium.dissolutionsolute + solvent crystallization solution
23 Water Molecule H2O d+ d+ d- d- Water is a POLAR molecule O2- H+ H+ Draw the Lewis dot structure of a water molecule.Recall, oxygen has 6 valence electrons and hydrogen has one valence electron.The ‘electron cloud’ is more dense around the oxygen than the hydrogen. Therefore, the oxygen side of the molecule is more negatively charged and has a partial negative charge.The hydrogen have a lower electron density around them and receive a partial positive charge. This molecule does not have a formal (+) and (-) charge – as in an ionic compound.
25 Water Molecule What is a polar molecule? d-Hydrogenbondd+OHHow does the polarity of water effect this molecule?An individual water molecule consists of two hydrogen atoms bonded to an oxygen atom in a bent (V-shaped) structure.The oxygen atom in each O–H covalent bond attracts the electrons more strongly than the hydrogen atom.O and H nuclei do not share the electrons equally.– Hydrogen atoms are electron-poor compared with a neutral hydrogen atom and have a partial positive charge, indicated by the symbol δ+.– The oxygen atom is more electron-rich than a neutral oxygen atom and has a partial negative charge, indicated by the symbol 2δ-.Unequal distribution of charge creates a polar bond.
26 Hydrogen bonds occur between two polar molecules, or between different polar regions of one large macro-molecule.One “relatively” negative region is attracted to a second “relatively” positive region.OHElectronegativeatomsHydrogenbondHN
27 Interstitial Spaces Oil Non-polar "immiscible" Polar dissolved solid LayerWaterWaterPolarThis is an overly simplified model of spaces between water molecules. However, it is in these interstitial spaces that gases (e.g. oxygen and carbon dioxide) dissolve and solids also dissolve.red foodcoloring
28 Dissolving of solid NaCl Due to the arrangement of polar bonds in a water molecule, water is called a polar substance.Due to the asymmetric charge distribution in the water molecule, adjacent water molecules are held together by attractive electrostatic interactions.Energy is needed to overcome these electrostatic interactions.Unequal charge distribution in polar liquids, like water, makes them good solvents for ionic compounds.When an ionic solid dissolves in water, the partially negatively charged oxygen atoms of water surround the cations, and the partially positively charged hydrogen atoms in water surround the anions.Individual cations and anions are called hydrated ions.
29 Polar water molecules interact with positive and negative ions AnimationThe attraction of water dipoles for ions pulls ions out of a crystalline lattice and into aqueous solution. The ion-dipole forces exist in the solution as well,lessening the tendency for ions to return to the crystalline state. The combination of an ion in solution and the neighboring water dipoles to which it isattracted is called a hydrated ion.Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 468
30 Dissolving of solid NaCl saltNa+NaCl solidNaCl (aq)= Na+= Cl-Animation by Raymond ChangAll rights reserved.
31 Solvation First... Then... Solvation – the process of dissolving solute particles are surrounded by solvent particlesFirst...The interactions that determine the solubility of a substance in a liquid depend on the chemical nature of the solute whether it is ionic or molecular) rather than on its physical state (solid, liquid, or gas).• Two examples:1. Forming a solution of a molecular species in a liquid solvent2. Formation of a solution of an ionic compoundSolutions of molecular substances in liquids– London dispersion forces, dipole-dipole interactions, and hydrogen bonds that hold molecules to other molecules are weak.– Energy is required to disrupt these interactions, and unless some of that energy is recovered in the formation of new, favorable solute-solvent interactions, the increase in entropy on solution formation is not enough for a solution to form.– For solutions of gases in liquids, the energy required to separate the solute molecules is ignored (H2 = 0) because molecules are already separated – it is necessary to only consider the energy required to separate the solvent molecules (H1) and the energy released by new solute-solvent interactions (H3).1. Nonpolar gases are most soluble in nonpolar solvents because H1 and H3 are both small and of similar magnitude.2. Nonpolar gases are less soluble in polar solvents than in nonpolar solvents because H1 >> H3.3. Solubilities of nonpolar gases in water increase as the molecular mass of the gas increases.– All common organic liquids, whether polar or not, are miscible; the strengths of the intermolecular attractions are comparable, the enthalpy of solution is small, and the increase in entropy drives the formation of a solution.– If predominant intermolecular interactions in two liquids are very different from one another, they may be immiscible, and when shaken with water, they form separate phases or layers separated by an interface.– Only the three lightest alcohols are completely miscible with water; as the molecular mass of the alcohol increases, so does the proportion of hydrocarbon in the molecule, which leads to fewer favorable electrostatic interactions with waterHydrophilic and hydrophobic solutes– A solute can be classified as hydrophilic, meaning that there is an electrostatic attraction to water, or hydrophobic, meaning that it repels water.1. Hydrophilic substance is polar and contains O–H or N–H groups that can form hydrogen bonds to water; tend to be very soluble in water and other strongly polar solvents2. Hydrophobic substance may be polar but usually contains C–H bonds that do not interact favorably with water; essentially insoluble in water and soluble in nonpolar solvents– The difference between hydrophilic and hydrophobic substances has substantial consequences in biological systems.– Vitamins can be classified as either fat soluble or water soluble.1. Fat-soluble vitamins (Vitamin A) are nonpolar, hydrophobic molecules and tend to be absorbed into fatty tissues and stored there.2. Water-soluble vitamins (Vitamin C) are polar, hydrophilic molecules that circulate in the blood and intracellular fluids and are excreted from the body and must be replenished in the daily diet.solute particles are separated and pulled into solutionThen...
32 Dissolving of NaCl - - - O + + + + Cl- Na+ hydrated ions H Timberlake, Chemistry 7th Edition, page 287
33 Dissolving of Salt in Water Na+ionsWater moleculesCl-ionsWhen sodium chloride crystals are dissolved in water, the polar water molecules exert attracting forces which weaken the ionic bonds. The process of solution occurs the ions of sodium and chloride become hydrated.NaCl(s) + H2O Na+(aq) + Cl-(aq)
34 Dissolving of Salt in Water Cl-ionsNa+Water moleculesWhen sodium chloride crystals are dissolved in water, the polar water molecules exert attracting forces which weaken the ionic bonds. The process of solution occurs the ions of sodium and chloride become hydrated.NaCl(s) + H2O Na+(aq) + Cl-(aq)
35 Particle Model of a Solution Before mixingFresh waterWater moleculeAfter mixingSaltwater solutionWater moleculeChloride ion, Cl-Sodium ion, Na+