DRA10 Dissolution Solution Solubility
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Transcript of DRA10 Dissolution Solution Solubility
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Solutions are homogeneous mixtures of two
or more pure substances. In a solution, the solute is dispersed
uniformly throughout the solvent .
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Molecular Solutions Molecular compounds with similar
chemical structures and olarities tend to
be miscible. Homolo ous alcohol series have olar and
non-polar ends.
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Ionic Solutions
Solubility affected by: -
affects the solubility. Also called,
Lattice energy (energy holding the ions. to the charge on ions; larger charge means
. Inversely proportional to the size of the ion;
.
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Solubility increases with increasing ion size, due
soluble), Ca(OH) 2, Sr(OH) 2, Ba(OH) 2(mostsoluble lattice ener chan es dominant .
Energy of hydration increases with for smallerions than bigger ones; thus ion size. MgSO 4(mostsoluble),... BaSO 4 (least soluble.) Hydrationenergy dominant.
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How does a solid
dissolve into a liquid?
What drives the
dissolution process?
What are the energetics
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1. Solvent molecules attracted to surface ions.
2. Each ion is surrounded by solvent molecules.3. Enthalpy ( H) changes with each interactionro en or orme .
Ionic solid dissolving in water
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1. Solvent molecules attracted to surface ions.
2. Each ion is surrounded by solvent molecules.3. Enthalpy ( H) changes with each interactionro en or orme .
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The ions are solvated
(surrounded bysolvent).If the solvent is water,
the ions arey ra e .The intermolecular
-dipole.
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To determine the enthalpy
,process into 3 steps.
.particles.
2. Separation of solventparticles to make holes.
3. Formation of new
solute and solvent.
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Enthalpy Changes in Solution
The enthalpychange of theoverall process
depends on
H for .
Start
n
EndStart
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Enthalpy changes during dissolution
Hsoln = H1 + H2 + H3
The enthalpy ofsolution, Hsoln , can
e e er pos ve ornegative.
Hsoln (MgSO 4)= -91.2 kJ/mol --> exothermic Hsoln (NH 4NO 3)= 26.4 kJ/mol --> endothermic
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Dispersal of energy inthe s stem.
Number of microstates
(arrangements) in thesys em.
. , is the favored state
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Entro chan es durin dissolution
change in entropy.1. Separation of solute
particles.
2. Separation of solvent .3. Formation of new
interactions between soluteand solvent.
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SAMPLE EXERCISE 1 Assessing Entropy ChangeIn the process illustrated below, water vapor reacts with excess solid
.reaction is
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Entropy Usuall FavorsMaking SolutionsBecause There Are More
Possible Arrangements of
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G = H - T SSolubility increases with T if G becomes morenega ve w en ncreasesWhen S is positive, -T S is negative and G
will increase when T increases.
When S is negative, -T S is positive and G.will decrease when T increases.
CompareKCl(s) K+ (aq) + Cl - (aq) S positiveCe SO s 2 Ce 3+ a + 3 SO 2- a S ne ative
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Ni(s) + HCl(aq) NiCl 2(aq) + H 2(g) NiCl2(s)dry
original solute by evaporating the solvent.
If you cant, the substance didnt dissolve, it reacted.
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Saturated solution
Solvent holds as muchsolute as is possible ata empera ure.
Undissolved solidremains in flask.Dissolved solute is indynamic equilibrium
w so so u eparticles.
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Unsaturated SolutionLess than themaximum amount ofsolute for thattem erature isdissolved in thesolvent.
o so rema ns nflask.
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upersa ura eSolvent holds more solute than is normally
.These solutions are unstable; crystallization canoften be stimulated by adding a seed crystal orscratching the side of the flask.
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,
How much solute can be dissolved in a solution?
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ac ors ec ng o u ySolute-Solvent Interactions o ar qu s en o sso ve n po ar so ven s. Miscible liquids: mix in any proportions. Immiscible li uids: do not mix. Intermolecular forces are important: water and ethanol are
miscible because the broken hydrogen bonds in both pure- . The number of carbon atoms in a chain affect solubility: the
more C atoms the less soluble in water.
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Factors Affecting SolubilitySolute-Solvent Interactions
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Factors Affecting SolubilitySolute-Solvent Interactions
The number of -OH groups within a moleculeincreases solubility in water.
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Solute-Solvent Interactions
Generalization: like dissolves like. The more polar bonds in the molecule, the better itdissolves in a polar solvent.
The less polar the molecule the less it dissolves in apolar solvent and the better is dissolves in a non-polar solvent.
e wor so s o no sso ve ecause e s rongintermolecular forces in the solid are not re- .
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Factors Affecting SolubilityPressure Effects Solubility of a gas in a liquid is a function of thepressure o e gas. The higher the pressure, the more molecules of gas
of a gas molecule striking the surface and enteringthe solution.
Therefore, the higher the pressure, the greater the solubility.
The lower the pressure, the fewer molecules of gas are close to the solvent and the lower the
.
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Factors Affecting Solubility
Experience tells us that sugar dissolves better in.
As temperature increases, solubility of solids.
Sometimes, solubility decreases as temperature. . .
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Chemists use the axiomlike dissolves like:Polar substances tend todissolve in polar solvents.
to dissolve in nonpolarsolvents.
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intermolecularattractions betweensolute and solvent,
the more likely theso u e w sso ve.Example: ethanol in water
Ethanol = CH 3CH 2OHIntermolecular forces = H-bonds; dipole-dipole; dispersion
Ions in water also have ion-dipole forces.
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hydrogen bonding) isvery soluble in water.Cyclohexane (which
only has dispersionforces) is not water-soluble.
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Vitamin A is soluble in nonpolar compounds
. Vitamin C is soluble in water.
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Whichv am n swater-solublean w c sfat-soluble?
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In general, thesolubility of gases inwater increases withincreasing mass.
y Larger molecules
ave s rongerdispersion forces.
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QuickTime and aTIFF (LZW) decompressor
are needed to see this picture.
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liquids and solidsdoes not changeIncreasing
appreciably with
pressure.
above
solution But, the solubility of a
gas in a liquid isforcesmore gasto dissolve.
its pressure.
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g g
whereg
the gas;
constant for that gas inthat solvent
P g is the partialressure of the as
above the liquid.
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Tem erature De endenceof Gas Solubility G = H - T S S is negative -T S is positive G becomes more positive
w en ncreases Therefore, solubility
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,
solubility of solidsolutes in liquidsolvents increases
with increasingempera ure.
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The opposite is true of.
temperature drivesgases out of solution.
Carbonated soft drinks
stored in therefrigerator.
arm a es ave essO2 dissolved in themthan cool lakes.