Solutions/WaterSolutions/Water

Mr. ChanMr. Chan Northwestern UniversityNorthwestern University

Day 9/15Day 9/15

45 Discuss HW/Quiz/Labs/Review45 Discuss HW/Quiz/Labs/Review 45 Quiz45 Quiz 60 Solutions60 Solutions 60 Lunch60 Lunch 90 Labs90 Labs 75 Review/Intervention/Conferences75 Review/Intervention/Conferences

Solution FormationSolution Formation

What is a solution?What is a solution? Common examples?Common examples?

How do you make one?How do you make one? What affects a solution?What affects a solution?

Affecting Rate vs. Affecting AmountAffecting Rate vs. Affecting Amount

Determining SolubilityDetermining Solubility Saturated solutionSaturated solution

Maximum amount of solute for a given amount of solvent at constant Maximum amount of solute for a given amount of solvent at constant temperaturetemperature

Unsaturated solutionUnsaturated solution Solution that contains less solute than a saturated solutionSolution that contains less solute than a saturated solution

Supersaturated solutionSupersaturated solution Solution that contains more solute than it can hold at a given Solution that contains more solute than it can hold at a given

temperaturetemperature SolubilitySolubility

Amount that dissolves in a given quantity of a solvent at a given tempAmount that dissolves in a given quantity of a solvent at a given temp Show Table of SolubilitiesShow Table of Solubilities

Miscible vs. ImmiscibleMiscible vs. Immiscible 2 liquids miscible if dissolve in each other2 liquids miscible if dissolve in each other Immiscible = insoluble in one anotherImmiscible = insoluble in one another

Factors that Determine Rate of Factors that Determine Rate of DissolvingDissolving

How can you make something dissolve How can you make something dissolve faster or slower?faster or slower? Nature of solvent and soluteNature of solvent and solute StirringStirring TemperatureTemperature Surface AreaSurface Area

Affecting Solubility of Solutions Affecting Solubility of Solutions and and

of Gas in Liquidof Gas in Liquid Temperature effectsTemperature effects

Increase temperature, increase solubilityIncrease temperature, increase solubility Gas/Liquid – increase temp, decrease Gas/Liquid – increase temp, decrease

solubilitysolubility Pressure effectsPressure effects

Only for gases: increase pressure, increase Only for gases: increase pressure, increase solubilitysolubility

Henry’s lawHenry’s law Solubility of gas proportional to pressure of Solubility of gas proportional to pressure of

gas above liquidgas above liquid MentosMentos/Diet Coke/Diet Coke

Calculating Molarity of SolutionCalculating Molarity of Solution

ConcentrationConcentration Measure of amount of solute dissolved in solventMeasure of amount of solute dissolved in solvent Dilute (small amount solute) vs. Concentrated (large amount of Dilute (small amount solute) vs. Concentrated (large amount of

solute)solute) MolarityMolarity

Number of moles of solute dissolved per liter of solutionNumber of moles of solute dissolved per liter of solution Molarity = moles/volumeMolarity = moles/volume Moles = M x V Moles = M x V

ExamplesExamples A) 0.70 mol NaCl, volume 250 mL – what is molarity?A) 0.70 mol NaCl, volume 250 mL – what is molarity? B) 36.0 grams glucose (180 g) in 2.0 L – what is molarity?B) 36.0 grams glucose (180 g) in 2.0 L – what is molarity? C) How many moles solute in 250 mL of 2.0M CaCl2? Grams?C) How many moles solute in 250 mL of 2.0M CaCl2? Grams?

Calculating DilutionsCalculating Dilutions

Moles of solute before dilution = moles of solute Moles of solute before dilution = moles of solute after dilutionafter dilution Number of moles of solute does not change when Number of moles of solute does not change when

solution is dilutedsolution is diluted M1 x V1 = M2 x V2M1 x V1 = M2 x V2 ExamplesExamples

A) need 250 mL of 0.20M NaCl, but you only have A) need 250 mL of 0.20M NaCl, but you only have 1.0M NaCl1.0M NaCl

B) 5 mL of 1.0M KOH with 1L 0.5M KOH – explainB) 5 mL of 1.0M KOH with 1L 0.5M KOH – explain

Determining percent by volume Determining percent by volume and percent by massand percent by mass

Percent by volume (%(v/v)) = volume of Percent by volume (%(v/v)) = volume of solute/solution volume x 100%solute/solution volume x 100%

Percent (mass/volume) = mass of Percent (mass/volume) = mass of solute/solution volume x 100%solute/solution volume x 100%

Think: juice packets, fruit punch, etc.Think: juice packets, fruit punch, etc. ExamplesExamples

A) percent by volume of ethanol when 75 mL A) percent by volume of ethanol when 75 mL of ethanol diluted to volume of 250 mL with of ethanol diluted to volume of 250 mL with waterwater

b) 2.7 grams of CuSO4 in 75 mL of solution. b) 2.7 grams of CuSO4 in 75 mL of solution. Calc percent (m/v) of solution.Calc percent (m/v) of solution.

Calculating Molality and Mole Calculating Molality and Mole FractionFraction

Molality – number of moles of solute dissolved per Molality – number of moles of solute dissolved per kilogram of solventkilogram of solvent Used in Colligative properties problemsUsed in Colligative properties problems

ExamplesExamples What is molality of solution prepared by dissolving 10.0 grams of What is molality of solution prepared by dissolving 10.0 grams of

NaCl in 600.0 g of waterNaCl in 600.0 g of water Mole FractionMole Fraction

Ratio of moles of solute to total number of moles of solvent and Ratio of moles of solute to total number of moles of solvent and solutesolute

ExamplesExamples What is mole fraction of each component in a solution made by What is mole fraction of each component in a solution made by

mixing 300.0 grams of ethanol and 500.0 grams of water?mixing 300.0 grams of ethanol and 500.0 grams of water?

Colligative PropertiesColligative Properties

Depend only on number of particles dissolved in Depend only on number of particles dissolved in given mass of solventgiven mass of solvent

Volatile vs. Nonvolatile solventsVolatile vs. Nonvolatile solvents Solution with nonvolatile solute – lower VP than pure Solution with nonvolatile solute – lower VP than pure

solventsolvent Proportional to number of particles the solute makes in Proportional to number of particles the solute makes in

solution (NaCl vs. glucose)solution (NaCl vs. glucose)

Boiling Point ElevationBoiling Point Elevation Increase in BP due to soluteIncrease in BP due to solute

Freezing Point DepressionFreezing Point Depression Decrease in FP due to soluteDecrease in FP due to solute

BP Elevation and FP DepressionBP Elevation and FP Depression

Change in temp = Kb x molalityChange in temp = Kb x molality Kb = molal boiling point elevation constantKb = molal boiling point elevation constant

Kb H2O = 0.512 C/mKb H2O = 0.512 C/m ExampleExample

What is the boiling point of a 2.00m NaCl solution?What is the boiling point of a 2.00m NaCl solution? FP DepressionFP Depression Change in temp = Kf x molalityChange in temp = Kf x molality

Kf – molal freezing point depression constantKf – molal freezing point depression constant Kf H2O = 1.86 C/mKf H2O = 1.86 C/m

ExampleExample What is the freezing point of a 2.00m NaCl solution?What is the freezing point of a 2.00m NaCl solution?

Calculating Molar Mass Calculating Molar Mass

Working backwards from FP/BP formulasWorking backwards from FP/BP formulas ExampleExample

9.20 g compound in 35.0 g of water boils at 9.20 g compound in 35.0 g of water boils at 102 degrees Celsius. What is the molar mass 102 degrees Celsius. What is the molar mass of the solute? Assume that the solute exists of the solute? Assume that the solute exists as molecules, not ions. as molecules, not ions.

Colloids and SuspensionsColloids and Suspensions

Suspensions – mixtures where some of the Suspensions – mixtures where some of the particles will settle slowly upon standingparticles will settle slowly upon standing Particles are much larger than those in a solutionParticles are much larger than those in a solution

Colloids – mixtures containing particles that are Colloids – mixtures containing particles that are intermediate in size between suspensions and intermediate in size between suspensions and solutionssolutions Examples: gelatin, smoke, milk, glueExamples: gelatin, smoke, milk, glue

Tyndall effectTyndall effect Scattering of visible light in all directionsScattering of visible light in all directions

HydratesHydrates

Water in a crystalWater in a crystal Compare hydrates to anhydrous solidsCompare hydrates to anhydrous solids Forces holding water molecules not very strongForces holding water molecules not very strong

EffloresceEffloresce To lose water of hydrationTo lose water of hydration

HygroscopicHygroscopic Compounds that remove moisture from the airCompounds that remove moisture from the air

DessicantsDessicants Drying agents, silica gel, packets in electronicsDrying agents, silica gel, packets in electronics

DeliquescentDeliquescent Remove water from air to dissolve completely to form solutionsRemove water from air to dissolve completely to form solutions

Lab – Supersaturation (A/W Lab – Supersaturation (A/W #31)#31)

Objectives: Experimental experience with Objectives: Experimental experience with supersaturationsupersaturation

Techniques: Start this experiment first.Techniques: Start this experiment first. Air cool instead of ice water bath – 20 Air cool instead of ice water bath – 20

minutesminutes Work on other experiment while you waitWork on other experiment while you wait Lab report, conferences about feedback, Lab report, conferences about feedback,

grades, etc.grades, etc. Questions: No Going FurtherQuestions: No Going Further

Lab – Factors Affecting Solution Lab – Factors Affecting Solution Formation (A/W #30)Formation (A/W #30)

Objectives: Experimental data on Factors Objectives: Experimental data on Factors that you’re familiar withthat you’re familiar with

Questions: No “Design Experiment”Questions: No “Design Experiment”