Ch. 14/15 Solids, Liquids and Solutions

Ch. 14/15 Solids, Liquids and Solutions

Intermolecular ForcesDipole-dipole attraction Between particles with charged sideshttp://dwb4.unl.edu/ChemAnime/DIPOLED/DIPOLED.html Hydrogen bonds - StrongestBetween Hs & F, O, N on other moleculesDispersion forces - WeakestCaused by electrons shifting towards one end of a molecule. Forces of attraction between different molecules rather than bonding forces within the same molecule.

2Water: The Magnificent DipoleOne side of water is negatively charged because the oxygen atom keeps the shared electrons longer than the hydrogen atoms. As a result the oxygen side isnegatively charged and the hydrogen side of water is positively charged.OIt is its polarity andhydrogen bonding that give water its many unusual Properties!

i.e. high boiling point, expansion upon freezing, and surface tensionHydrogen bonds - StrongestBetween Hs & F, O, N on other moleculesIceLiquid

Water is always trying to pull itself into a tight ball as long as there is nothing nearby that has a charge on it. Therefore, this surface is not repelling water; its simply not attracting it and keeping water from doing what it does naturally.

Water pulls on itself so much that it forms a skin. Its called surface tension.Wax does not repel waterWeve heard that wax or oils repel water. But that isnt true. Water is so attracted to other water molecules that anything between them is squeezed out of the way.OOOildropletOOOForces and PhasesSubstances with very little intermolecular attraction exist as gasesSubstances with strong intermolecular attraction exist as liquidsSubstances with very strong intermolecular (or ionic) attraction exist as solidsVapor gaseous state of a substance that is not normally a gas at room temperature.

Volatile evaporates rapidly (due to weak intermolecular forces)Ex. thin liquids

Viscous evaporates slowly(due to strong intermolecular forces)Ex. thick liquidsV is for Vocabulary!

Phase Differences

Three Phases of Matter

LiquidsA decrease in the average kinetic energy of gas particles causes the temperature to decrease. As it cools, the particles tend to move more slowly, if they slow down enough, attractive forces - called van der Waals forces pull them very close together so they can only slip & slide past each other.

It is now in liquid form!Condensation Change of a gas to a liquid

The Nature of LiquidsThe conversion of a liquid to a gas or vapor below its boiling point is called Vaporization (occurs at the surface of a liquid) In an open container, this process is called Evaporation Particles near the surface with enough kinetic energy that happen to bounce in the right direction escape!Microscopic view of a liquid near its surface.

The Nature of LiquidsEventually the particles will lose energy and return to the liquid state, or condense.What are the odds that they will return to the original liquid?What if we cover the container?So, the particles begin to evaporate, then some begin to condense. Eventually, the number of particles evaporating will equal the number condensing & the space above the liquid will be saturated with vapor

A dynamic equilibrium now exists whereRate of evaporation = rate of condensation

Note that there will still be particles that evaporate and condenseBut, there will be no NET changeIt will not look like there are changes taking place!

Evaporation is a cooling processCooling occurs because particles with the highest energy escape firstParticles left behind have lower average kinetic energies; thus the temperature decreasesSimilar to removing the fastest runner from a race- the remaining runners have a lower average speedEvaporation helps to keep our skin cooler on a hot day!The Nature of LiquidsA liquid will evaporate faster when heated because the added heat increases the average kinetic energy needed to overcome the attractive forces so more particles have enough energy to escape!

If you were to add a drop of water below the tube to the left what would happen?It would rise to the top & evaporate.What would it do to the surface of the mercury? (push it down!)Vapor Pressure pressure exerted by vapor!(

Since different liquids evaporate at different rates, they have different vapor pressures (at the same temps)(

Which liquid is the most volatile?Yes! Diethyl Ether! It depressed the mercury the most (highest vapor pressure!)Vapor Pressures of Liquids

Which is the most volatile liquid here?

Diethyl etherIt has the highest vapor pressure at any Temp.

Which has the strongest forces of attraction?Water22A liquid boils when its vapor pressure equals the external pressure, so the boiling point changes if the external pressure changes.Bubbles form throughout the liquid, rise to the surface, and escape into the airNormal boiling point- is when the vapor pressure of a liquid equals standard pressure. (1 atm)

The boiling point (bp) is the temperature at which the vapor pressure of the liquid is equal to the external pressure on the liquid

VPBPDirect relationship!Normal bp of water = 100 oCHowever, in Denver = 95 oC, since Denver is 1600 m above sea level and average atmospheric pressure is about 85.3 kPa (Recipe adjustments?)In pressure cookers, which reduce cooking time, water boils above 100 oC due to the increased pressure

Boiling Point of Water at Various LocationsLocationFeet above sea levelPatm (kPa)Boiling Point (C)Top of Mt. Everest, Tibet29,0283270Top of Mt. Denali, Alaska20,32045.379Top of Mt. Whitney, California14,49457.385Top of Mt. Washington, N.H.6,29378.693Boulder, Colorado5,43081.394New York City, New York10101.3100Death Valley, California-282102.6100.3Vapor Pressures of Liquids

Normal bp whencrossing hereAt any pt. on a curve line, liquid is boiling27SOLIDSIf you cool a liquid, the particles lose kinetic energy and slow down.If they slow down enough, extra forces of attraction pull them in so close together that they can only vibrate in place.Freezing change of a liquid to a solid.

Types of SolidsMolecular solidsMetallic solidsIonic solidsCovalent network solids (diamonds)

29Crystals or Crystalline SolidsParticles of crystals are arranged in repeating geometric patterns

NaClRepresentation of Components in a Crystalline SolidCrystal Lattice:The orderly, regular, 3-dimensional arrangement of particles (atoms, ions, etc.) in a crystal.

31Unit CellThe smallest portion of a crystal lattice that shows the three-dimensional pattern of the entire lattice

Ex. A cubic lattice system has 3 types of unit cellsTable salt crystals are shaped like cubes.

Diamond, a form of carbon, is also a crystalline solid.the crystals are shaped something like pyramids.

Non-crystalline solidsMany solids do not form crystals- AmorphousTheir molecules do not arrange into repeating patternsoften because they are too large.No definite melting pointExamples:Glass - also called a super-cooled liquidmany plastics, soot, asphalt, butter

PHASE CHANGESPHASE CHANGES change is physical state (melting, freezing, boiling, condensing, sublimation, deposition) BOTH PHASES present during a phase changeTemperature remains constant during a phase change.Sublimation change of a solid directly to a gas (dry ice, iodine, snow)Deposition change of a gas directly to a solid.

Heat (kilojoules)Temperature (C)00-202060

A-B = Solid ice, temperature is increasing. Particles gain kinetic energy, vibration of particles increases.Heating and cooling curve for water heated at a constant rates.Ice

B-C = Solid starts to change state from solid to liquid. Temperature remains constant as energy is used to break inter-molecular bonds. 0CH2O (s) H2O (l)

C-D = temperature starts to rise once all the solid has melted. Particles gain kinetic energy.Liquid water

D-E = Liquid starts to vaporize, turning from liquid to gas. The temperature remains constant as energy is used to break inter-molecular forces.H2O () H2O (g)100C

E-F = temperature starts to rise once all liquid is vaporized. Gas particles gain kinetic energy.steam

The heating/cooling curve for water

Water phase changes

Temperature remains __________during a phase change.constantKinetic energy increasing on slopesKE not changing during phase changesBoilingcondensationMeltingfreezingPhase DiagramRepresents phases as a function of temperature and pressure.

45Classification of MatterRecallAlso called solutionsSoluteThe part of a solution that gets dissolved the part in lesser quantityThe part of a solution that does the dissolving the part in greater quantitySolventSalt in salt waterSugar in soda drinksCarbon dioxide in soda drinksWater in salt waterWater in soda

Aqueous Solutions water solutionsSolutions occur in all 3 phases!SoluteSolventExampleGasGasAirLiquidGasWater Vapor in AirSolidGasMothballsGasLiquidSeltzer WaterLiquidLiquidAntifreeze in radiator, cocktailSolid LiquidSalt waterGasSolidWhipped creamLiquidSolidFillings: Hg in AgSolidSolidAlloys: Brass, etc.

like dissolves likeTwo substances with similar intermolecular forces are likely to be soluble in each other.non-polar molecules are soluble in non-polar solventsEx. Grease in gasoline

Ionic compounds & polar molecules are soluble in polar solventsEx. Ethanol in water; salt in water12.2When a salt dissolves in water, the positive ions are attracted to the slightly negative ends of the water molecules and the negative ions are attracted to the slightly positive ends of the water molecules. They dissociate (separate)

The ions are more strongly attracted to each other. but they become surrounded by water molecules and cant get back together!

Solvation where solvent molecules surround solute particles.Dissolving of solid sodium chloride.

Water: the Universal SolventOONa+Cl-OOOSOLVATION of NaCl

http://www.mpcfaculty.net/mark_bishop/NaCl_dissolves.htmhttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf

SOLUBILITYA measure of how much a gas, liquid, or solid will dissolve in a solvent.Factors Effecting SolubilityThe solubility of MOST solids increases with an increase in temperature.The rate at which solids dissolve increases with increasing surface area of the solid. (crush them & stir them!)The solubility of gases increases with decreases in temperature.The solubility of gases increases with an increase of pressure above the solution.ThereforeSolids tend to dissolve best when: Heated Stirred Ground into smaller particlesGases tend to dissolve best when: The solution is cooler Pressure is higherCO2 in and out of water

When you see bubbles, its a heterogeneous mixture not a solution!SolutionMixture

Salt (NaCl) is very soluble in water. 350 g/liter. However, if water evaporates, there will be too much salt for the water to hold in solution. The salt begins to form crystals.

A lake near Death Valley is supersaturated with salt causing the salt to crystallize out.

Once a year the company who owns the lakes lets visitors into the area to collect salt crystals.

These are some of the salt crystals collected.Solubilitymaximum mass of solute that will dissolve in 100 g of solvent at a given temperaturevaries with tempbased on a saturated solutionTemperature and SolubilitySolid solubility and temperature

solubility increases with increasing temperaturesolubility decreases with increasing temperature12.4Solubility Chart

A solution that contains the maximum amount of solute that may be dissolved under existing conditions is saturated.A solution that contains less solute than it can is unsaturated.A solution that contains more dissolved solute than it should is supersaturated.

SolubilitySATURATED SOLUTIONno more solute dissolves

UNSATURATED SOLUTIONmore solute dissolves

SUPERSATURATED SOLUTIONbecomes unstable, crystals formconcentrationSolubility Chart

Colligative PropertiesColligative Properties are those that depend on the concentration of particles in a solution, not upon the identity of the solute. Boiling Point Elevation Freezing Point Depression Vapor Pressure DepressionMore particles in solution bigger effect on the coll. property!Higher bp, lower fp, etc.Change in Boiling Point Common Applications of Boiling Point Elevation

Change in Freezing Point Common Applications of Freezing Point Depression

Propylene glycolEthylene glycol deadly to small animals

Concentration

70Concentrations of SolutionsThe amount of solute in a solution is given by its concentration.Concentration can be expressed qualitatively or quantitatively

Dilute contains small amount of soluteConcentrated contains large amount of solute(words)(numbers)Molarity(M)=moles soluteliters of solution

*Volume of solution MUST be in Liters!We will use something called Molarity!Ex. What is the molarity of a solution made by dissolving 3.5 moles of NaCl in a 4.3L solution?3.5 moles NaCl4.3 L solution= 0.81 M NaCl(aq)Molarity can be labeled M or mol/LHandy in conversion factors!PROBLEM: Dissolve 5.00 g of NiCl2 in enough water to make 250 mL of solution. Calculate the Molarity.Step 1: Calculate moles of NiCl2

Step 3: Calculate Molarity[NiCl2] = 0.154 M

Step 2: convert mL to L250 mL .250LStep 1: Change mL to L.250 mL x 1L/1000mL = 0.250 LStep 2: Calculate.Moles = (0.0500 mol) (0.250 L) = 0.0125 moles

Step 3: Convert moles to grams.(0.0125 mol)(90.00 g/mol) = 1.13 g oxalic acidmoles = MVWhat mass of oxalic acid, H2C2O4, isrequired to make 250. mL of a 0.0500 Msolution?*Rearrange formula to solve for moles.1 LLearning CheckHow many grams of NaOH are required to prepare 400. mL of 3.0 M NaOH solution?

1)12 g2)48 g3) 300 g

Preparing SolutionsWeigh out a specific mass of solid solute and dissolve in a given quantity of solvent.Dilute a concentrated solution to give one that is less concentrated.

M1V1 = M2V2How would you make 250 mL of 3.0 M HCl from a 6 M stock solution of HCl?M1V1 = M2V2(250 mL) (3.0 M) = (6 M) (X)

X = 125 mL

How would you make would require some words in the answer!So, Add enough water to 125 mL of 6 M HCl to bring the total volume to 250 mL.Miscible where liquids dissolve in each other.

Ex. Ethanol in waterSuspensions and ColloidsSuspensions and colloids are NOT solutions. Suspensions: The particles are so large that they settle out of the solvent if not constantly stirred.Colloids: The particles are intermediate in size between those of a suspension and those of a solution.The Tyndall EffectColloids scatter light, making a beam visible. Solutions do not scatter light.

Which glass contains a colloid?solutioncolloidTypes of ColloidsExamplesDispersing MediumDispersed SubstanceColloid TypeFog, aerosol spraysGasLiquidAerosolSmoke, airborne bacteriaGasSolidAerosolWhipped cream, soap sudsLiquidGasFoamMilk, mayonnaiseLiquidLiquidEmulsionPaint, clays, gelatinLiquidSolidSolMarshmallow, StyrofoamSolidGasSolid foamButter, cheeseSolidLiquidSolid emulsionRuby glassSolidSolidSolid sol