solutions chapter 6 what are solutions? solution: homogeneous mixture of 2 or more substances...
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What Are Solutions?What Are Solutions?
• Solution: homogeneous mixture of 2 Solution: homogeneous mixture of 2 or more substancesor more substances– Solid, liquid, or gasSolid, liquid, or gas– Solvent: dissolving mediumSolvent: dissolving medium– Solute: substance that dissolvesSolute: substance that dissolves– When in solution, you cannot distinguish When in solution, you cannot distinguish
solvent and solutesolvent and solute
What is a Solution?What is a Solution?
• Soluble – a substance that can Soluble – a substance that can dissolve in a given solventdissolve in a given solvent– Miscible: two liquids that can dissolve in Miscible: two liquids that can dissolve in
each othereach other•Example: water and antifreezeExample: water and antifreeze
• Insoluble – substance cannot dissolveInsoluble – substance cannot dissolve– Immiscible: two liquids that cannot Immiscible: two liquids that cannot
dissolve in each otherdissolve in each other•Example: oil & waterExample: oil & water
Why Do Some Substances Why Do Some Substances Dissolve and not Others?Dissolve and not Others?
• To dissolve, solute particles must To dissolve, solute particles must dissociate from each other and mix dissociate from each other and mix with solvent particleswith solvent particles– Attractive forces between solute and Attractive forces between solute and
solvent must be greater than attractive solvent must be greater than attractive forces within the soluteforces within the solute
• Process of surrounding solute Process of surrounding solute particles with solvent particles is particles with solvent particles is called SOLVATIONcalled SOLVATION– In water, it is also called HYDRATIONIn water, it is also called HYDRATION
Aqueous Solutions of Ionic Aqueous Solutions of Ionic CompoundsCompounds
• Remember:Remember:– Water molecules are polar (+ and – ends)Water molecules are polar (+ and – ends)– Water molecules are in constant motionWater molecules are in constant motion
• When you put salt in water, water When you put salt in water, water molecules collide with surface of crystalmolecules collide with surface of crystal– Charged ends of water attract ions of saltCharged ends of water attract ions of salt– Dipole interaction (water/salt) is stronger Dipole interaction (water/salt) is stronger
than ions in crystal, so it pulls them awaythan ions in crystal, so it pulls them away
Aqueous Solutions of Molecular Aqueous Solutions of Molecular CompoundsCompounds
• Water is also a good solvent for many Water is also a good solvent for many molecular compounds (Example: molecular compounds (Example: sugar)sugar)– Sugar has many O-H bonds (polar)Sugar has many O-H bonds (polar)– When water is added, the O-H bond When water is added, the O-H bond
becomes a site for hydrogen bonding with becomes a site for hydrogen bonding with waterwater
– Water’s hydrogen bonds pulls the sugar Water’s hydrogen bonds pulls the sugar molecules apartmolecules apart
– Oil is not a good solute because it has Oil is not a good solute because it has many C-H bonds (not polar) and few or no many C-H bonds (not polar) and few or no O-H (polar) bondsO-H (polar) bonds
Factors that Affect Solvation Factors that Affect Solvation RateRate• Increase Solvation Rate (Dissolve Increase Solvation Rate (Dissolve
Faster) by:Faster) by:– Agitation (stirring)Agitation (stirring)– Increase surface area (make particles Increase surface area (make particles
smaller)smaller)– Temperature (make it hotter)Temperature (make it hotter)
• All these increase the number of All these increase the number of collision between water and the collision between water and the solute solute
SolubilitySolubility• Only a limited amount of solute can Only a limited amount of solute can
dissolve in a given amount of solventdissolve in a given amount of solvent
• Every solute is unique for the solventEvery solute is unique for the solvent
• This is ‘Solubility’ – the amount of This is ‘Solubility’ – the amount of solute that can dissolve in a given solute that can dissolve in a given amount of solvent at a specified amount of solvent at a specified temperature and pressuretemperature and pressure
Solubility ContinuedSolubility Continued
• Solubility can also be understood at the Solubility can also be understood at the particle level:particle level:– As particles collide, some particles are As particles collide, some particles are
deposited back to the solutedeposited back to the solute– Some particles are removed from the solute.Some particles are removed from the solute.– When the rate of deposit equals the rate of When the rate of deposit equals the rate of
solvation, then the solution is SATURATEDsolvation, then the solution is SATURATED
• Saturated Solution – no more solute can Saturated Solution – no more solute can be dissolved in the solvent at this be dissolved in the solvent at this temperature and pressuretemperature and pressure
• Unsaturated Solution – there is still room Unsaturated Solution – there is still room for more solute to be dissovedfor more solute to be dissoved
Factors that Affect SolubilityFactors that Affect Solubility
• Most substances are MORE soluble at Most substances are MORE soluble at high temperature than at lowhigh temperature than at low– If you dissolve a substance until If you dissolve a substance until
saturated at high temperature and then saturated at high temperature and then reduce the temperature, the solution reduce the temperature, the solution becomes “supersaturated”becomes “supersaturated”
– Supersaturated solutions are unstableSupersaturated solutions are unstable•A small change makes the solute reappearA small change makes the solute reappear
•Rock candy worked that way. How?Rock candy worked that way. How?
Gas Solubility is Opposite Gas Solubility is Opposite SolidsSolids• Gas solubility DECREASES with Gas solubility DECREASES with
temperaturetemperature
• Gas solubility decreases with shakingGas solubility decreases with shaking
Electrolytes and Colligative Electrolytes and Colligative PropertiesProperties
• When solutions are made, the When solutions are made, the physical properties of the solutions physical properties of the solutions are affected by the number of are affected by the number of particle dissolvedparticle dissolved– Colligative: depending on the collectionColligative: depending on the collection
Colligative PropertiesColligative Properties
1.1. Electrolytes vs non-electrolytesElectrolytes vs non-electrolytes– Ionic compounds ARE electrolytes Ionic compounds ARE electrolytes
because they form ions in solution that because they form ions in solution that conduct electricityconduct electricity
– Molecular compounds ARE NOT Molecular compounds ARE NOT electrolytes because they do not electrolytes because they do not conduct electricityconduct electricity
2.2. Vapor Pressure LoweringVapor Pressure Lowering• Adding a non-volatile solute lowers the Adding a non-volatile solute lowers the
vapor pressure of the solution (vs. vapor pressure of the solution (vs. solvent)solvent)
• More solute More solute more vapor pressure more vapor pressure loweringlowering
Colligative PropertiesColligative Properties3.3. Boiling Point ElevationBoiling Point Elevation
• Because vapor pressure is lowered, it takes Because vapor pressure is lowered, it takes more energy to make it boilmore energy to make it boil• Boiling point temperature is raisedBoiling point temperature is raised• Boiling point elevation is directly proportional to Boiling point elevation is directly proportional to
solution molalitysolution molality• What is the benefit of adding salt to boiling water for What is the benefit of adding salt to boiling water for
pasta?pasta?
4.4. Freezing Point DepressionFreezing Point Depression• Freezing point temperature is loweredFreezing point temperature is lowered• Solute particles interfere with attractive forces Solute particles interfere with attractive forces
of solventof solvent• Freezing point of a solution is always lower Freezing point of a solution is always lower
than the freezing point of a pure solventthan the freezing point of a pure solvent• FP Depression is directly proportional to FP Depression is directly proportional to
molalitymolality
Colligative PropertiesColligative Properties
5.5. Osmosis and Osmotic PressureOsmosis and Osmotic Pressure• Diffusion: mixing of gasses or liquids Diffusion: mixing of gasses or liquids
through random motionsthrough random motions
• Osmosis is diffusion of solvent through a Osmosis is diffusion of solvent through a semi permeable membrane from high semi permeable membrane from high solvent concentration to lower solvent solvent concentration to lower solvent concentrationconcentration– Living cells use this to get materials in/out of Living cells use this to get materials in/out of
cellscells
Colligative PropertiesColligative Properties• Example: Salt/waterExample: Salt/water
– During Osmosis, Water molecules move During Osmosis, Water molecules move both directions through membraneboth directions through membrane•But only water can move through the But only water can move through the
membranemembrane•So pure water builds up on one side of the So pure water builds up on one side of the
membranemembrane•Water/salt builds up on the other.Water/salt builds up on the other.
– Higher concentration of water on one Higher concentration of water on one side creates:side creates:•Osmotic pressureOsmotic pressure•A pressure or push to equalize the water/salt A pressure or push to equalize the water/salt
concentrationsconcentrations•Pressure depends on concentration of solutePressure depends on concentration of solute
Colligative Properties - Colligative Properties - AntifreezeAntifreeze
Antifreeze Colligative Properties
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