CORNELL NOTES In the body of the notes: Take notes in class in the format that is most comfortable to you: Outline, text, shorthand, sketches, diagrams, examples Do NOT copy notes word for word think as you write rephrase abbreviate organize Use the side to list main points Organize ideas (if you get bored do this in class!) Ask questions such as might be on a test or that you wonder about Use thinking skills to question, bring ideas together, and extend them At the bottom, summarize main ideas at appropriate intervals

SOLUTIONS A solution is a homogeneous mixture; particles are evenly distributed throughout the mixture. Proportions may vary Uniform ratio throughout the mixture 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. (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.

SOLUTIONS Solns homogeneous mixture evenly distributed particles variable proportions uniform ratio liquid soln clear. particles are not visible, do not settle, and can not be filtered. Not suspensions: particles of a susp are visible, can be filtered, and settle. Not colloids: particles of a colld exhibit Tyndall effect, yet do not settle. (TYNDALL effect: the scattering of light by particles such as headlights in fog, flashlight thru dilute milk) A solution will not exhibit the Tyndall effect.

SOLUTIONS Solns homogeneous mixture evenly distributed particles variable proportions uniform ratio liquid soln clear. particles are not visible, do not settle, and can not be filtered. Not suspensions: particles of a susp are visible, can be filtered, and settle. Not colloids: particles of a colld exhibit Tyndall effect, yet do not settle. (TYNDALL effect: the scattering of light by particles such as headlights in fog, flashlight thru dilute milk) A solution will not exhibit the Tyndall effect. Define soln Describe soln Are all solns liquid? Contrast liquid soln with susp and colloids

SOLUTIONS Solns homogeneous mixture evenly distributed particles variable proportions uniform ratio liquid soln clear. particles are not visible, do not settle, and can not be filtered. Not suspensions: particles of a susp are visible, can be filtered, and settle. Not colloids: particles of a colld exhibit Tyndall effect, yet do not settle. (TYNDALL effect: the scattering of light by particles such as headlights in fog, flashlight thru dilute milk) A soln will not exhibit the Tyndall effect. Define soln Describe soln Are all solns liquid? Contrast liquid soln with susp and colloids Solutions are homogenous mixtures with variable proportions and uniform ratios. Separate components are not visible/discernible.

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. Molecular substances that do not ionize when dissolved do not conduct electricity and are called NONELECTROLYTES.

NONELECTROLYTES Molecular substances that do not ionize when dissolved do not conduct electricity and are called NONELECTROLYTES.

SOLUTIONS ELECTROLYTES Conduct electricity IONIC COMPOUNDS DISSOCIATE into ions SOME POLAR MOLECULAR COMPOUNDS IONIZE to form ions NONELECTROLYTES Do not conduct electricity OTHER POLAR MOLECULAR COMPOUNDS DO NOT IONIZE

Review 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 molecular/covalent compounds A substance whose water solutions do not conduct electricity is a non- electrolyte. ◦ Many molecular/covalent compounds

What factors affect the rate of dissolution? The experiment provides a model; it demonstrates some ideas well but is not entirely accurate!

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

What does “like dissolves like” mean? This experiment demonstrates “like dissolves like” Use your observations and knowledge of soap to explain this.

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

Exothermic and Endothermic Exothermic: Some substances release heat when they dissolve and feel warm. ◦ Hand-warmers Endothermic: Some substances absorb heat when they dissolve and feel cold. ◦ Cold-packs

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!

PPM and PPB x/1,000,000 x/1,000,000,000 Serial dilutions are often used ◦ 1x, 10x, 100x, 1000x, etc. Often used in environmental studies of water and air. Contaminants may be significant in the PPB range!

Percent by volume mL of solute /100 mL of solution 30% rubbing alcohol 30mL isopropanol/100mL of solution x 100% = 30% v/v isopropyl alcohol (v/v means volume to volume) The solvent is usually the substance present in greater quantity.

Percent by mass g of solute/100 mL of solution Often used in medicine… ◦ 5% glucose or.9% saline are two examples.9% saline solution.9 g salt/100 mL solution x 100% =.9 % m/v solution of saline (m/v means mass to volume)

Mass per volume g solute/1000 mL solution 40 g NaOH/1000 mL solution This is not really very helpful, but you can figure out how much NaOH is in a certain volume: 20. mL x 40. g/1000 mL =.80 g NaOH

Molarity M = mol solute/liter of solution Chemists use this because it lets us work concentration into stoichiometry problems 40 g NaOH x 1 mol NaOH = 1 M NaOH = 1 mol NaOH 1 L soln 40 g NaOH 1 L soln

Molality…one letter difference! m = mol solute/kg of solvent 40 g NaOH x 1 mol NaOH = 1 m NaOH = 1 mol NaOH 1 kg solvent 40 g NaOH 1 kg solvent Chemists sometimes use this because volume of liquids changes with temperature. Soon, we will be studying the effect of concentration on properties as temperature changes.

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 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

M 1 V 1 = M 2 V 2 How do you prepare 100 mL of 0.40 M NaCl from a stock of 2.0 M NaCl? M 1 V 1 = M 2 V M ( x ) = 0.40 M (100 mL) x = 20 mL Measure 20. mL of stock and dilute to a total volume of 100 mL in a “volumetric flask.” Note: volume can be any units, but must be consistent.