Chapter 13 13.1 What is a solution? • mixture – two or more subs. that are physically combined – no form./any proportion – subs. retain properties – easily separated by physical means • solution – homogeneous mixture – solute – subs. being dissolved(sugar) • particles are 0.1 to 2 nm in size – solvent – subs. doing the dissolving(water) Solution Solute Solvent salt water radiator fluid pop/cola salt(s) antifreeze(l) CO2 (g) water(l) water(l) water(l) dental filling brass filter on gas mask Hg (l) Cu (s) poisonous gas(g) Ag, Sn, Cu (s) Zn (s) charcoal(s) air ????? ????? O2 (g) ??? (l) ??? (s) N2 (g) ??? (g) ??? (g) • suspension – a two phase heterogeneous mixture that separates upon standing • particles are >1000 nm in size – clay in water – dust in air • colloid – a two phase heterogeneous mixture that remains mixed(usually due to like charged particles) • particles are 2 to 1000 nm in size – milk – fat and casein dispersed in whey – glue water – glue dispersed in water • Tyndall effect – scattering of light caused by undissolved particles – gaseous or liquid solutions = dissolved - no Tyndall effect – suspensions or colloids = undissolved – positive for Tyndall effect • separation techniques for mixtures – filter/decant - colloids and suspensions – evaporation – remove liquids from solids – chromatography – separates solutions by molecular size – distillation – separates solutions by boiling • fractional distillation – separation by boiling point differences 13.2 Concentration and Molarity • concentration – the ratio of solute to solvent – qualitative • dilute • concentrate • quantitative 1) parts per million(ppm) • • # of solute particles to solution particles 1 ppm = 1 solute particle to 1,000,000 total particles • 1 drop of food coloring in 40 gal H2O • for aqueous solutions = mg solute/L solution What is the concentration in ppm for a solution that has 0.0380 grams of lead in 300.0 mL of tap water solution? X ppm = 1000 mg x 0.0380 g Pb x 1000 mL 1g x 300.0 mL sol x 1L X ppm = 127 mg/L or ppm http://planetforlife.com/co2history/index.html • Atmospheric carbon dioxide during the last four ice ages. (http://planetforlife.com/co2history/index.html) 2) parts per billion(ppb) – micrograms/L (µg/L) – 1 ppb = • • 1 mL of water in an Olympic swimming pool 7 people in the world at current population • Sixteen pesticides have been detected in eight brand-name baby foods, according to a study by the Environmental Working Group and the National Campaign for Pesticide Policy Reform, two public interest groups based in Washington, DC. • In their study, the EWG and the NCPPR collected a random sampling of 76 jars of baby food from grocery store shelves in Denver, Philadelphia, and San Francisco. The group chose fruits and vegetables babies most commonly eat during their first year of life. Of these, 53% harbored traces of one pesticide, and 18% had two or more pesticides. Plums contained the highest amounts at 46 parts per billion and peaches contained 29 parts per billion. Pears had the highest number of multiple pesticides overall (five). 3) molarity(M) • • # of particles to volume of solution M = mol solute/L solution – vinegar is composed of 5.00 grams of acetic acid(HC2H3O2) in 100.0 mL of solution. What is the M of vinegar? M = 1 mole acetic acid x 5.00 g acetic acid 60.06 g acetic acid x 0.1000 L solution M = 0.833 mol/L or M 4) molality (m) – – # particles solute to mass solvent moles of solute to kilograms of solvent • used in calculating freezing point depressions and boiling point elevations 5) karat (k) – concentration of Au in alloys • 24 k gold = pure Au • 12 k gold = 50% Au & 50% other metal(s) 6) mass % (% m/m) – – mass of solute per mass solution used in industry In a regular Coke there is 39 grams of sugar in 355 grams of pop, what is mass %? % m/m = 39 grams sugar/355 grams pop % m/m = 11% sugar 7) volume % (%v/v) – volume solute per volume solution 13.3 Solubility and the Dissolving Process • solubility – the ability of a subs. to dissolve @ specific T and P conditions – hydrophilic • • • • • “water loving” dissolve in water vitamin C most ionic compounds polar molecules – hydrophobic • “water fearing” • insoluble in water • soluble in fats or oils – vitamin A – wax – styrofoam • general rule of solubility – “like dissolves like” – soaps/detergents dissolve in both laundry ball • polar end of soap – attaches to water • nonpolar end of soap – attaches to dirt/oil/fat – miscible – mutually soluble – immiscible – does not dissolve • dissolving – the breaking up of a solute to the smallest particles that make up the solute • particles 0.1 to 2 nm • NaCl breaks apart to Na+ & Cl- ions • sugar break apart to C12H22O11 molecules – occurs at surface of solute (anim) – methods utilized to increase dissolving rate of a solid in a liquid • powdering/crushing – more surface area • stirring – fresh solvent in contact with solute • heating • dissolving mechanisms and NRG changes 1) solute(s) solute(l) • • • NRG is added to solute for phase change dissociation – separation in to ions/molecules endothermic 2) solvent moves apart to allow solute to enter • • • solvent makes room for solute NRG needed to move solvent apart endothermic 3) solute and solvent attract • • • solvation/hydration decrease entropy – release NRG exothermic • if dissolv. mech. 1 & 2 > 3 – dissolving is endothermic – heating increases dissolving – solution feels cold during dissolving – temp. of solution increases during crystallizing • cold pack • most solutes • if dissolv. mech. 1 & 2 < 3 – dissolving exothermic – heating decreases dissolving • cooling increases dissolving – not very common • NaOH • solubility of ionic compounds – vary due to many factors • soluble – more than 1 g/100 g H2O • slightly soluble – 0.1 to 1 g/100 g H2O • insoluble – less than 0.1 g/100 g H2O • equilibrium – two opposing processes occurring simultaneously – melting and freezing – dissolving and crystallizing • if a solution is at equilibrium – undissolved solute remains in solvent • crystals in bottom of container – saturated solution – solvent is “holding” the maximum amount of solute at those conditions – saturated solutions contain undissolved solute • if dissolving is occurring faster than crystallizing(not at equillibrium) – no undissolved solute – all solute dissolves – unsaturated solution – solvent is holding less than the maximum amount of solute • dissolving > crystallizing • each substance has different solubility @ different temperatures – solubility curve – figure 12, page 472 • supersaturated solution – a unique phenomena – solvent holds more than the maximum amount of solute @ the specified conditions • more solute than a saturated solution – not common – very easily disturbed • honey • liquid hand warmers • solubility of gases in liquids – different than solids/liquids – T affect solubility of gases • solubility increases as T of solvent decreases – less molecular motion – gas particles remain isolated – cold liquids dissolve more gases » cloudy ice – hot liquids dissolve less gases » thermal pollution – P affect solubility • Henry’s law – solubility of a gas in a liquid is directly related to the P of that gas above the liquid – fizz keeper 13.4 Physical Properties of Solutions • electrolyte – substance that when dissolved or molten conducts electricity • carry e-‘s • ions need to be present – ionic compounds dissociate when dissolved NaCl(s) Na+(aq) + Cl-(aq) – acid ionization HCl(l) H+(aq) + Cl-(aq) – What are the electrolytes in Gatorade? – In Gatorade, the key electrolytes are the minerals sodium, potassium and chloride. When athletes sweat, they lose electrolytes such as sodium, potassium, and chloride that are essential to hydration and muscle function. Unlike water and other beverages that are not scientifically formulated, Gatorade is lab-tested to ensure it helps replenish the electrolytes lost in sweat and stimulates thirst so athletes will ingest an adequate amount of fluid and electrolytes to stay better well-hydrated compared to when using beverages without electrolytes, particularly sodium.¹²³ http://www.gatorade.com/frequently_asked_questions/default.aspx • strong electrolyte – completely ionize/dissociate – lots of ions 10 NaCl(s) 10 Na+(aq)+ 10 Cl-(aq) • weak electrolyte – partially ionize/dissociate – few ions 10 HC2H3O2(l) H+(aq) + C2H3O2-(aq) + 9 HC2H3O2(aq) • nonelectrolyte – no ionization/dissociation – no ions – molecules(not acids) • colligative properties – any prop. that affects the solvents physical prop. because of the number of solute particles – adding solute to solvent changes the prop. of the solvent 1) vapor pressure • • • decreases when solute is added to solvent vapor P = P created when a confined liquid evap. less solvent part. at surface to evap. – – – less evap. = less P tap water evap. slower than distilled water sim lab 2) freezing point – decreases when solute is added to solvent – freezing pt. – T at which the vapor P of the solid = vapor P of liquid – since vapor P of liquid is reduced the Tf is reduced – solutions freeze at lower T than pure solvents • more solute particles = lower freezing points • (simulated lab) • freezing pt. depression calculation ΔTf = m x Kf x i m = molality(mol solute/kg solvent) Kf = freezing pt constant(water = 1.86o C/m) i = van’t Hoff factor = # particles dissoc./ionized • freezing pt depression sample problem – What T does 175 grams of water freeze if 22.5 grams of sodium chloride is added? ΔTf = m x Kf x i ΔTf = 1 mol NaCl x 22.5 g NaCl x 1.86o C x 2 58.44 g NaCl x 0.175 Kg H2O x ΔTf = 8.18o C normal Tf = 0o C - ΔTf = 8.18o C new Tf = - 8.18o C m • How many grams of calcium chloride are needed to lower the freezing point of 750.0 grams of water to -6.55o C? ΔTf = 6.55o C X m = 6.55o C____ 1.86o C/m x 3 X m = 1.17 m X g CaCl2 = 110.98 g CaCl2 x 1.17 mol CaCl2 x 0.7500 Kg 1 mol CaCl2 x X g CaCl2 = 97.4 g CaCl2 Kg 3) boiling point – increases when solute is added to solvent • boiling point = T at which the vapor P of the liquid is equal to atmospheric P • • • Tb – H2O = 100o C @ 1 atm solute reduces vapor P of solvent more NRG added to get same vapor P • • T of liquid will be higher to attain vapor P = atm. P solutions have higher boiling points than pure solvents • more solute particles = higher boiling points ΔTb = m x Kb x i m = molality Kb = boiling point constant (H2O = 0.510o C/m) i = van’t Hoff factor My mom always adds salt to the water when she cooks noodles so the noodles cook faster. She adds about 2.0 grams of salt to 1.0 liter of water. What T does her water boil? ΔTb = 1 mol NaCl x 2.0 g NaCl x 0.510o C x 2 58.44 g NaCl x 1.0 Kg x m ΔTb = 0.035o C normal Tb = 100o C + ΔTb = 0.035o C new Tb = 100.035o C • How many grams of sugar(C12H22O11) would need to be added to 500.0 grams of water to increase the boiling point to 105.0o C? ΔTb = 5.0o C X m = 5.0o C________ 0.510o C/m x 1 X m = 9.8 m X g = 342.34 g x 9.8 mol x 0.5000 Kg 1 mol x 1 Kg X g = 1700 g sugar • surfactants – substance that concentrates at the interface between two phases – solid-liquid, liquid-liquid, liquid-gas – detergent – synthetic surfactant(not natural) • generally made from vegetable oil and sulfuric acid • often liquid – soap – natural surfactant • generally made from sodium/potassium salts of natural animal fatty acids • often solid – emulsifying agent - substance, such as soap or eggs, that allows two immiscible liquids to remain dispersed in one another • Sodium Lauryl Sulfate – SLS – An Industrial Detergent • SLS is an Engine Degreaser! And it’s in nearly every cleansing product we use from toothpaste to beauty soap. SLS is generally made from petroleum oil and sulfuric acid, and may still contain traces of both. It makes personal products foamy, and is a strong detergent that strips away the skin’s precious oils in addition to removing dirt. Ironically, the FDA actually uses it as a skin irritant to test the anti-irritation properties of various drugs. • Sodium Laureth Sulfate • Sodium Laureth Sulfate (SLES) is one of the most common shampoo ingredients. In fact most personal hygiene products contain this specific ingredient. SLES is a washing surfactant, in other words a washing detergent. Imagine it as a car polish that returns the shine by removing the top layer of the paint.