Presentation on theme: "SOLUTIONS A solution is a homogeneous mixture; particles are evenly distributed throughout the mixture. Amounts may vary between solutions (variable proportions)"— Presentation transcript:
SOLUTIONS A solution is a homogeneous mixture; particles are evenly distributed throughout the mixture. Amounts may vary between solutions (variable proportions) But The ratio of amounts is the same throughout a particular solution For instance, you might like a little sugar in your Koolaid or a lot, but within a glass of Koolaid, the sugar is mixed evenly
SOLUTIONS, cont. A liquid solution is clear. The particles are not visible, do not settle, and can not be filtered. A solution differs from a suspension in that the particles of a suspension are visible, can be filtered, and settle. A solution differs from a colloid in that the particles of a colloid exhibit Tyndall effect., yet do not settle. Remember… (TYNDALL effect: the scattering of light by particles such as headlights in fog, flashlight through Jello or dilute milk) A solution will not exhibit the Tyndall effect.
Cherry Kool-aid Red powder: flavor and color White crystals: sugar Clear liquid: water One substance dissolved in another ◦ Solute: the substance being dissolved ◦ Solvent: the substance that dissolves the solute Sugar is the SOLUTE (smaller quantity) Water is the SOLVENT (larger quantity)
Types of Solutions Gas (solvent is gas) ◦ Gas into Gas: air ◦ Liquid into Gas: humidity ◦ Solid into Gas: air pollution Liquid (solvent is liquid) ◦ Gas into Liquid: pop ◦ Liquid into Liquid: vinegar ◦ Solid into Liquid: sweet tea Solid (solvent is solid) ◦ Gas into Solid: absorbent charcoal ◦ Liquid into Solid: dental fillings ◦ Solid into Solid: alloys of metal
The Dissolving Process Two factors affect the dissolving process: dissolution ◦ The constant motion of the particles (There’s that good old kinetic molecular theory again!) ◦ The polarity of the solute and solvent (Recall that polarity is when a compound has partial charges because of uneven distribution of charges)
Steps of the Dissolving Process 1. Moving solvent particles cluster around solute molecules or particles at the surface of the solid. 2. Solvent molecules pull solute off of the solid surface and into solution. 3. Moving solvent particles continue to spread solute evenly throughout the solution, The process repeats itself as fresh layers of the solute are exposed.
1.Solvent particles cluster around solute particles at the surface. 2. Solvent particles pull solute particles away from surface, into solution. 3.Moving solute particles continue to spread solute evenly through solution. MOLECULAR
1.Solvent particles cluster around solute particles at the surface. 2. Solvent particles pull solute particles away from surface, into solution. 3.Moving solute particles continue to spread solute evenly through solution. IONIC
IONIC COMPOUNDS When an ionic substance dissolves in water, the forces of the solvent pulling on the ions is stronger than the forces holding the ions together. The ions separate. This is called DISSOCIATION Because charged ions are present in an ionic solution, ionic solutions conduct electricity and are called ELECTROLYTES. EXAMPLE: NaCl
MOLECULAR COMPOUNDS Certain polar substances form ions when they dissolve in water. This process is called IONIZATION. Because ions are formed, the solution conducts electricity. These substance are also ELECTROLYTES. EXAMPLE: HCl, HC 2 H 3 O 2
MOLECULAR COMPOUNDS Other polar substances do not ionize in water. Because ions are not formed, the solution does not conduct electricity. These substances that do not ionize in water and do not conduct electricity are called NON-ELECTROLYTES. EXAMPLE: sugar
ELECTROLYTES: substances that conduct electricity when dissolved in water Ionic substances that separate into ions (dissociate) or polar molecular substances that form ions (ionization) when dissolved conduct electricity and are called ELECTROLYTES.
Review A substance whose water solutions do not conduct electricity is a non- electrolyte. ◦ Many covalent compounds A substance that separates into ions (dissociates) or forms ions (ionizes) in a water solution conducts electricity and is called an electrolyte ◦ All ionic and some covalent compounds
COMPOUNDS THAT DISSOLVE IN WATER ELECTROLYTES DO CONDUCT ELECTRICITY IONIC COMPOUNDS DISSOCIATE INTO IONS SOME POLAR MOLECULAR COMPOUNDS IONIZE NON- ELECTROLYTES DO NOT CONDUCT ELECTRICITY OTHER POLAR MOLECULAR COMPOUNDS DISSOLVE WITH NO FORMATION OF IONS
FactorsSolid in LiquidGas in Liquid TEMPERATURETemp > Rate > Temp > Rate < AGITATIONAgitation > Rate > Agitation > Rate < SIZE OF PARTICLES Size < (surface area >) Rate > NA PRESSURENAPressure > Rate > WHY?The solute particles are less energetic than solvent The solute particles are more energetic than solvent FACTORS THAT AFFECT THE RATE OF DISSOLUTION
Think BIG Recall the Pop and Mentos experiment! The pop “explodes” because the dissolved gas rapidly leaves the solution because the candy gives it surfaces to collect on (nucleation sites).
Particles in Solutions Solvents with non-polar molecules dissolve non-polar substances ◦ Oil, grease, dry cleaning fluid, paint, turpentine Solvents with polar molecules dissolve polar substances ◦ Water dissolves sugar, ionic compounds LIKE DISSOLVES LIKE
Terms Soluble: capable of being dissolved in a particular solvent Insoluble: incapable of being dissolved in a particular solvent Miscible: liquids that dissolve freely in any proportion Immiscible: liquids that are not soluble in each other
Detergents and emulsifiers Grease is non-polar Water is polar DETERGENT has ◦ A non-polar end that dissolves the grease ◦ A polar end that dissolves in the water to rinse it away NONPOLAR DETERGENT POLAR GREASEWATER
CRAFTY CHEMISTRY Artists use physical properties to create inspiring beauty! ART and SCIENCE
Solubility There are limits to the amount of solute that will dissolve in a given amount of solvent at a given temperature There are some general terms: ◦ Unsaturated ◦ Saturated ◦ Super-saturated
Unsaturated a solution that can dissolve more of a given solute at a certain temperature ◦ A crystal of solute added to an unsaturated solution will dissolve When you add a second spoon of sugar to your cup of tea, it dissolves. The tea was an unsaturated solution.
Saturated a solution that has dissolved all of the solute that it can at a certain temperature ◦ A crystal of solute added to a saturated solution will drop to the bottom, un-dissolved. When you add three spoons of sugar to your tea, some sugar drops to the bottom, undissolved. It is a saturated solution. DYNAMIC EQUILIBRIUM exists: ◦ changing but balanced. ◦ Some solid dissolves, but as some dissolves, some re- crystallizes
Super-saturated an unstable solution that contains more solute than a saturated solution at a certain temperature ◦ A crystal of solute added to a super-saturated solution will cause crystallization. So will any disruption of the unstable solution. ◦ Make a saturated solution at an elevated temperature and cool it slowly. At the lower temperature, the solute will remain dissolved in an unstable situation. If disrupted, the solute crystallizes. Hot-packs and rock candy
Max g of solute that will dissolve in 100 g of solvent at a given temperature
Concentration: the amount of solute in a given amount of solvent or solution Dilute: a relatively small amount of solute in a relatively large amount of solvent Concentrated: a relatively large amount of solute in a relatively small amount of solvent We can do better!
Percent by volume mL of solute /100 mL of solution
Dilutions: a concentrated solution is diluted by adding more solvent to get the desired concentration. M 1 V 1 = M 2 V 2 Moles before dilution = Moles after dilution ◦ M = molarity = mol/L ◦ V = volume = L ◦ M x V = mol/L x L = # mol of solute
Dilutions: a concentrated solution is diluted by adding more solvent to get the desired concentration. The # of moles before dilution is equal to the # of moles after dilution. The same # of moles is present in more solvent. The concentration (M, molarity) changes, the volume (V) changes, but not the # of moles of solute (M x V). ◦ Volume units may vary from L, but must be consistent within problem. So, M 1 V 1 = M 2 V 2 SEE EXAMPLE PROBLEMS
Colligative Properties Colligative…sounds like collective The number or concentration of dissolved particles affects properties of solution It does not matter WHAT the particles are It only matters HOW MANY particles there are Collectively (all together) the amount of the particles has an effect
Boiling Point Elevation The more particles of solute dissolved in a solution, the higher the boiling point. More particles of solute at the surface mean fewer solvent particles can vaporize, thus raising the boiling point. EX] antifreeze dissolved in the coolant of our cars raises the boiling point to keep our engine from overheating.
Freezing Point Depression The more particles of solute dissolved in a solution, the lower the freezing point. More particles of solute interfere with crystal formation, lowering the freezing point. EX] antifreeze dissolved in the coolant of our cars lowers the freezing point to keep our engine running in cold weather EX] Salt on the sidewalks melts the ice