SolutionsSolutions

The Nature of Aqueous The Nature of Aqueous SolutionsSolutions A solution is a homogeneous mixture.A solution is a homogeneous mixture. The substance that is dissolved is the The substance that is dissolved is the

solute.solute. The substance that does the The substance that does the

dissolving is the solvent. (Water is dissolving is the solvent. (Water is known as the universal solvent due to known as the universal solvent due to its ability to dissolve a wide range of its ability to dissolve a wide range of solutes)solutes)

How do solutes How do solutes dissolve?dissolve? Ionic solids are all soluble in water.Ionic solids are all soluble in water. The “positive” ends of a water molecule The “positive” ends of a water molecule

are attracted to the anion of the solid.are attracted to the anion of the solid. The “negative” ends of a water molecule The “negative” ends of a water molecule

are attracted to the cation of the solid.are attracted to the cation of the solid. This process is called hydration and This process is called hydration and

results in the ionic solid being pulled results in the ionic solid being pulled apart, or dissolved.apart, or dissolved.

What is an electrolyte?What is an electrolyte? Solutions that conduct an electric Solutions that conduct an electric

current efficiently contain strong current efficiently contain strong electrolytes.electrolytes.

Strong electrolytes are substances Strong electrolytes are substances that completely ionize in water.that completely ionize in water.

Three types of compounds are Three types of compounds are classified as strong electrolytes.classified as strong electrolytes.

Strong ElectrolytesStrong Electrolytes The following are classified as strong The following are classified as strong

electrolytes:electrolytes:– Soluble salts (see the handout of the Soluble salts (see the handout of the

solubility rules)solubility rules)– Strong acids (HCl, HBr, HI, HStrong acids (HCl, HBr, HI, H22SOSO44, HNO, HNO33,,

HClOHClO33, HClO, HClO44))– Strong bases (group 1A hydroxides, and Strong bases (group 1A hydroxides, and

Ba(OH)Ba(OH)22

What is an acid?What is an acid? According to the Arrhenius According to the Arrhenius

definition, an acid is any definition, an acid is any substance that produces Hsubstance that produces H++ ions ions when it is dissolved in water.when it is dissolved in water.

Strong acids are those acids in Strong acids are those acids in which every molecule ionizes into which every molecule ionizes into HH++ ions and anions. ions and anions.

What is a strong base?What is a strong base? According to the Arrhenius According to the Arrhenius

definition, a strong base is any definition, a strong base is any soluble ionic compound containing soluble ionic compound containing the hydroxide ion (OHthe hydroxide ion (OH--).).

When these compounds dissolve in When these compounds dissolve in water, the cations and OHwater, the cations and OH-- ions ions separate and move independently.separate and move independently.

What is a weak What is a weak electrolyte?electrolyte? Weak electrolytes are substances that Weak electrolytes are substances that

exhibit a small degree of ionization in exhibit a small degree of ionization in water and therefore conduct an electric water and therefore conduct an electric current inefficiently.current inefficiently.

The most common weak electrolytes The most common weak electrolytes are weak acids and weak bases.are weak acids and weak bases.

An example of a weak acid is acetic acid An example of a weak acid is acetic acid (HC(HC22HH33OO22). An example of a weak base ). An example of a weak base is ammonium hydroxide (NHis ammonium hydroxide (NH44OH)OH)

What is a What is a nonelectrolyte?nonelectrolyte? Nonelectrolytes are substances that Nonelectrolytes are substances that

dissolve in water but do not produce dissolve in water but do not produce any ions.any ions.

Organic/covalent molecules are Organic/covalent molecules are nonelectrolytes. Table sugar nonelectrolytes. Table sugar (C(C1212HH2222OO1111) is an example of a soluble ) is an example of a soluble compound that is a nonelectrolyte. compound that is a nonelectrolyte. This is because, when dissolved, the This is because, when dissolved, the sugar molecule remains intact. sugar molecule remains intact.

ConcentrationConcentration Concentrations of solutions are Concentrations of solutions are

expressed qualitatively and expressed qualitatively and quantitativelyquantitatively

Qualitative expressions include Qualitative expressions include the terms saturated, unsaturated, the terms saturated, unsaturated, and supersaturated.and supersaturated.

Concentration Concentration (continued)(continued) Saturated solution-a solution in which no Saturated solution-a solution in which no

more solute will dissolve at a given more solute will dissolve at a given temperature (the maximum has been temperature (the maximum has been dissolved)dissolved)

Unsaturated solution-a solution in which more Unsaturated solution-a solution in which more solute will dissolve at a given temperature solute will dissolve at a given temperature (less than the maximum has been dissolved)(less than the maximum has been dissolved)

Super-saturated solution-a solution that Super-saturated solution-a solution that contains higher-than-saturation concentration contains higher-than-saturation concentration of solute (a slight disturbance will cause of solute (a slight disturbance will cause crystallization)crystallization)

Quantitative Quantitative Expressions of Expressions of ConcentrationConcentration Percent by massPercent by mass MolarityMolarity MolalityMolality Dilution of solutionsDilution of solutions

Percent by MassPercent by Mass Percent by mass gives the mass of Percent by mass gives the mass of

solute per 100 mass units of solutionsolute per 100 mass units of solution Percent solute=Percent solute=mass of solute mass of solute x x

100%100% mass of solutionmass of solution

Mass of solution = mass of solute + Mass of solution = mass of solute + mass of solventmass of solvent

Percent by Mass Percent by Mass ProblemsProblems Calculate the mass of NiSOCalculate the mass of NiSO44 contained in 200. g contained in 200. g

of a 6.00% solution of NiSOof a 6.00% solution of NiSO44 A 6.00% solution of NiSOA 6.00% solution of NiSO44 contains 40.0 g of contains 40.0 g of

NiSONiSO44. Calculate the mass of the solution.. Calculate the mass of the solution. Calculate the mass of NiSOCalculate the mass of NiSO44 present in 200. mL present in 200. mL

of a 6.00% solution of NiSOof a 6.00% solution of NiSO44. The density of . The density of the solution is 1.06 g/mL at 25the solution is 1.06 g/mL at 25ooC.C.

What is the volume of a solution that is 15.0% What is the volume of a solution that is 15.0% Fe(NOFe(NO33))3 3 and contains 30.0 g of the solute? The and contains 30.0 g of the solute? The density of the solution is 1.16 g/mL at 25density of the solution is 1.16 g/mL at 25ooC.C.

MolarityMolarity Molarity-the moles of solute Molarity-the moles of solute

pervolume of solution in liters.pervolume of solution in liters.

MM = molarity = = molarity = moles of solutemoles of solute liters of solutionliters of solution

(solution = solvent + solute)(solution = solvent + solute)

Molarity ProblemsMolarity Problems Calculate the molarity of a Calculate the molarity of a

solution prepared by dissolving solution prepared by dissolving 11.5 g of solid NaOH in enough 11.5 g of solid NaOH in enough water to make 1.50 L of solution.water to make 1.50 L of solution.

Calculate the mass of Ba(OH)Calculate the mass of Ba(OH)22 required to prepare 2.50 L of a required to prepare 2.50 L of a 0.0600 0.0600 M M solution of Ba(OH)solution of Ba(OH)22..

MolalityMolality Molality-the number of moles of Molality-the number of moles of

solute per solute per kilogram of solventkilogram of solvent Molality = Molality = moles of solutemoles of solute

kilogram of solventkilogram of solvent

Molality ProblemsMolality Problems A solution is prepared by mixing A solution is prepared by mixing

1.00 g of ethanol with 100.0 g of 1.00 g of ethanol with 100.0 g of water to give a final volume of water to give a final volume of 101 mL. What is the molality? 101 mL. What is the molality? What is the molarity? What is the What is the molarity? What is the mass percent? What is the mole mass percent? What is the mole fraction?fraction?

Dilution of SolutionsDilution of Solutions Dilution occurs when more solvent Dilution occurs when more solvent

is added to a solution without is added to a solution without changing the amount of solute that changing the amount of solute that is present.is present.

VV11MM11 = V = V22MM22 For safety purposes when in a lab For safety purposes when in a lab

setting, concentrated solutions of setting, concentrated solutions of acids and bases are always added acids and bases are always added slowly to water.slowly to water.

Dilution ProblemsDilution Problems

How many mL of 18.0 How many mL of 18.0 MM H H22SOSO44 are required to prepare 1.00 L of are required to prepare 1.00 L of a a 0.900 0.900 MM solution of H solution of H22SOSO44??

Review of Solution Review of Solution ConcentrationConcentration The electrolyte in car batteries is The electrolyte in car batteries is

a 3.75 a 3.75 MM H H22SOSO44 solution that has a solution that has a density of 1.230 g/mL. What is density of 1.230 g/mL. What is the mass %, molality, and mole the mass %, molality, and mole fraction of the sulfuric acid?fraction of the sulfuric acid?

Factors Affecting Factors Affecting Solubility Solubility Solubility is the maximum amount Solubility is the maximum amount of solute that will dissolve in a of solute that will dissolve in a given amount of solvent at a given amount of solvent at a particular temperature.particular temperature.

Molecular StructureMolecular Structure The statement “like dissolves like” The statement “like dissolves like”

summarizes the formation of solutions summarizes the formation of solutions based on the structure of the molecules.based on the structure of the molecules.

““Like dissolves like” means that polar Like dissolves like” means that polar solvents dissolve ionic and polar solutes solvents dissolve ionic and polar solutes while nonpolar solvents dissolve while nonpolar solvents dissolve nonpolar solutes.nonpolar solutes.

The term miscibility is used to describe The term miscibility is used to describe the ability of one liquid to dissolve in the ability of one liquid to dissolve in another. (The observation of “like another. (The observation of “like dissolves like” still applies). dissolves like” still applies).

Example of Example of Differentiating Solvent Differentiating Solvent Properties Based on Properties Based on StructureStructure Decide whether liquid hexane or Decide whether liquid hexane or

liquid methanol is the more liquid methanol is the more appropriate solvent for the appropriate solvent for the substances grease (Csubstances grease (C2020HH4242) and ) and potassium iodide.potassium iodide.

Effect of Temperature Effect of Temperature on Solubilityon Solubility The solubility of most solid solutes The solubility of most solid solutes

increases with increasing increases with increasing temperature.temperature.

(exceptions include: Na(exceptions include: Na22SOSO44 and and CeCe22(SO(SO44))33))

The solubility of gases decreases The solubility of gases decreases with increasing temperature.with increasing temperature.

(example of this includes thermal (example of this includes thermal pollution)pollution)

Solubility GraphsSolubility Graphs Solubility curves are graphs that illustrate the Solubility curves are graphs that illustrate the

effect of temperature on the solubilities of effect of temperature on the solubilities of various salts.various salts.

Using the graph on p.496, answer the following Using the graph on p.496, answer the following questions:questions:*How many grams of KNO*How many grams of KNO33 will dissolve in 200 g will dissolve in 200 g of water at 70of water at 70ooC?C?*At what temperature will 80 g of KBr dissolve in *At what temperature will 80 g of KBr dissolve in 100 g of water?100 g of water?*Which solute’s solubility is least affected by *Which solute’s solubility is least affected by temperature?temperature?

Effect of Pressure on Effect of Pressure on Solubility Solubility Changing the pressure has no Changing the pressure has no

effect on the solubilities of either effect on the solubilities of either solids or liquids in liquids.solids or liquids in liquids.

The solubilities of gases in all The solubilities of gases in all solvents will increase as the solvents will increase as the partial pressure of the gases partial pressure of the gases increase.increase.

Henry’s LawHenry’s Law Henry’s law applies to gases that Henry’s law applies to gases that

do not react with the solvent in do not react with the solvent in which they dissolve.which they dissolve.

The law states that the pressure The law states that the pressure of a gas above the surface of a of a gas above the surface of a solution is proportional to the solution is proportional to the concentration of the gas in the concentration of the gas in the solution.solution.

Henry’s Law Henry’s Law (continued)(continued) The equation for Henry’s law is:The equation for Henry’s law is:

PPgasgas = kC = kCgasgas PPgasgas is the pressure of the gas above the is the pressure of the gas above the

solutionsolutionk is a constant for a particular gas and k is a constant for a particular gas and

solvent at a particular temperaturesolvent at a particular temperatureCCgasgas represents the concentration of the represents the concentration of the

dissolved gas; usually expressed as dissolved gas; usually expressed as molarity or mole fraction.molarity or mole fraction.

Calculations Using Calculations Using Henry’s LawHenry’s Law A certain soft drink is bottled so that at A certain soft drink is bottled so that at

2525ooC a bottle contains COC a bottle contains CO22 gas at a gas at a pressure of 5.0 atm over the liquid. pressure of 5.0 atm over the liquid. Assuming that the partial pressure of COAssuming that the partial pressure of CO22 in the atmosphere is 0.0004 atm, calculate in the atmosphere is 0.0004 atm, calculate the equilibrium concentration of COthe equilibrium concentration of CO22 in the in the soda both before and after the bottle is soda both before and after the bottle is opened. The Henry’s law constant for COopened. The Henry’s law constant for CO22 at 25at 25ooC is C is 32 L32 L.. atm/mol at 25 atm/mol at 25ooC. How does your C. How does your answer explain why soft drinks go flat answer explain why soft drinks go flat after being opened?after being opened?

Colligative PropertiesColligative Properties Colligative properties are physical Colligative properties are physical

properties that depend on the properties that depend on the number, not the kind, of solute number, not the kind, of solute particles in a given amount of solvent.particles in a given amount of solvent.

There are four important colligative There are four important colligative properties: vapor pressure lowering, properties: vapor pressure lowering, boiling point elevation, freezing point boiling point elevation, freezing point depression, osmotic pressuredepression, osmotic pressure

Lowering of Vapor Lowering of Vapor PressurePressure Solutions containing a nonvolatile liquid or a Solutions containing a nonvolatile liquid or a

solid as a solute always has a lower vapor solid as a solute always has a lower vapor pressure than the pure solvent.pressure than the pure solvent.

When a solute is dissolved, there are fewer When a solute is dissolved, there are fewer solvent molecules at the surface of the solvent molecules at the surface of the liquid. liquid.

Therefore, the solvent molecules vaporize Therefore, the solvent molecules vaporize at a slower rate than if no solute were at a slower rate than if no solute were present.present.

The lowering of the vapor pressure of a The lowering of the vapor pressure of a solvent due to the presence of a nonvolatile solvent due to the presence of a nonvolatile solute is summarized by Raoult’s Law.solute is summarized by Raoult’s Law.

Raoult’s LawRaoult’s Law The vapor pressure of a solvent in an The vapor pressure of a solvent in an

ideal solution is directly proportional to ideal solution is directly proportional to the mole fraction of the solvent in the the mole fraction of the solvent in the solution.solution.

PPsolventsolvent = X = Xsolventsolvent P P00solventsolvent

The lowering of the vapor pressure can The lowering of the vapor pressure can be expressed as:be expressed as:ΔΔPPsolventsolvent = X = XsolutesolutePP00

solventsolvent

Sample ProblemSample Problem Determine the vapor pressure Determine the vapor pressure

lowering of a sucrose solution lowering of a sucrose solution made by dissolving 50.0 g of made by dissolving 50.0 g of sucrose (Csucrose (C1212HH2222OO1111) in 117 g of ) in 117 g of water. The vapor pressure of water. The vapor pressure of pure water at 25pure water at 25ooC is 23.8 torr.C is 23.8 torr.

Sample Problem #2Sample Problem #2 Predict the vapor pressure of a Predict the vapor pressure of a

solution made by mixing 35.0 g of solution made by mixing 35.0 g of solid Nasolid Na22SOSO44 with 175 g water at with 175 g water at 2525ooC. The vapor pressure of pure C. The vapor pressure of pure water at 25water at 25ooC is 23.76 torr.C is 23.76 torr.

Sample Problem #3Sample Problem #3 At 40At 40ooC, the vapor pressure of pure C, the vapor pressure of pure

heptane is 92.0 torr and the vapor heptane is 92.0 torr and the vapor pressure of pure octane is 31.0 torr. pressure of pure octane is 31.0 torr. Consider a solution that contains Consider a solution that contains 1.00 mole of heptane and 4.00 moles 1.00 mole of heptane and 4.00 moles of octane. Calculate the vapor of octane. Calculate the vapor pressure of each component and the pressure of each component and the total vapor pressure above the total vapor pressure above the solution.solution.

Boiling Point ElevationBoiling Point ElevationA nonvolatile solute elevates the boiling point A nonvolatile solute elevates the boiling point

of of the solvent.the solvent. Boiling occurs at a temperature where the Boiling occurs at a temperature where the

vapor pressure is equal to 1 atm.vapor pressure is equal to 1 atm. Addition of a nonvolatile solute lowers vapor Addition of a nonvolatile solute lowers vapor

pressure.pressure. Therefore, a solution must be heated to a Therefore, a solution must be heated to a

higher temperature than the boiling point of higher temperature than the boiling point of the pure solvent to reach a vapor pressure of the pure solvent to reach a vapor pressure of 1 atm.1 atm.

Equation for Boiling Equation for Boiling Point ElevationPoint Elevation

∆T = Kbmsolute ∆T is the boiling point elevation Kb is the boiling point elevation

constant for the solvent msolute is the molality of the

solute

Calculating Boiling Calculating Boiling Point ElevationPoint Elevation Find the boiling point of a 1.25 Find the boiling point of a 1.25 mm

sucrose solution.sucrose solution. A solution was prepared by A solution was prepared by

dissolving 18.00 g glucose in 150.0 dissolving 18.00 g glucose in 150.0 g of water. The resulting solution g of water. The resulting solution was found to have a boiling point was found to have a boiling point of 100.34of 100.34ooC. Calculate the molar C. Calculate the molar mass of glucose.mass of glucose.

Freezing Point Freezing Point DepressionDepression When a solute is dissolved in a solvent, When a solute is dissolved in a solvent,

the freezing point of the solution is the freezing point of the solution is lower than that of the pure solvent.lower than that of the pure solvent.

This is the reason that compounds This is the reason that compounds such as sodium chloride and calcium such as sodium chloride and calcium chloride are spread on roadways to chloride are spread on roadways to prevent ice from forming in freezing prevent ice from forming in freezing weather.weather.

Equation for Freezing Equation for Freezing Point DepressionPoint Depression ∆∆T = T = KKffmmsolutesolute

∆∆T is the freezing point depressionT is the freezing point depression KKff is the freezing point depression constant is the freezing point depression constant mmsolute solute is the molality of the soluteis the molality of the solute

Calculating Freezing Calculating Freezing Point DepressionPoint Depression Calculate the freezing point of a 1.25 Calculate the freezing point of a 1.25 mm sucrose sucrose

solution.solution. What mass of ethylene glycol (CWhat mass of ethylene glycol (C22HH66OO22 = 62.1 = 62.1

g/mol), the main component of antifreeze, must g/mol), the main component of antifreeze, must be added to 10.0 L of water to produce a be added to 10.0 L of water to produce a solution for use in a car’s radiator that freezes solution for use in a car’s radiator that freezes at -10.0at -10.0ooF F

(-23.3(-23.3ooC)?C)? A sample weighing 0.546 g was dissolved in A sample weighing 0.546 g was dissolved in

15.0 g of benzene, and the freezing point 15.0 g of benzene, and the freezing point depression was determined to be 0.240depression was determined to be 0.240ooC. C. Calculate the molar mass of the sample.Calculate the molar mass of the sample.

The van’t Hoff FactorThe van’t Hoff Factor Colligative properties depend on the number of solute Colligative properties depend on the number of solute

particles in a given mass of solvent.particles in a given mass of solvent. The dissociation of electrolytes in aqueous solutions The dissociation of electrolytes in aqueous solutions

causes a greater change in these properties than a causes a greater change in these properties than a solution containing a nonelectrolyte (as in the previous solution containing a nonelectrolyte (as in the previous examples).examples).

One measure of the extent of dissociation of an One measure of the extent of dissociation of an electrolyte in water the van’t Hoff factor, electrolyte in water the van’t Hoff factor, ii, for the , for the solution.solution.

i = moles of particles/moles of solute ( or the number i = moles of particles/moles of solute ( or the number of ions per formula unit)of ions per formula unit)

The observed value of The observed value of ii is always slightly lower than is always slightly lower than the predicted value due to ion pairing. (see page 513).the predicted value due to ion pairing. (see page 513).

For problem solving purposes, use the ideal value of i For problem solving purposes, use the ideal value of i unless the problem indicates otherwise.unless the problem indicates otherwise.

Determining the van’t Determining the van’t Hoff factorHoff factor What is the value of the van’t Hoff What is the value of the van’t Hoff

factor, factor, ii, for the following strong , for the following strong electrolytes?electrolytes?a) Naa) Na22SOSO44

b) KOHb) KOH c) Alc) Al22(SO(SO44))33

d) SrSOd) SrSO44

Properties of Electrolyte Properties of Electrolyte SolutionsSolutions From the following solutions:From the following solutions:

0.010 0.010 mm Na Na33POPO440.020 0.020 mm CaBr CaBr220.020 0.020 mm KCl KCl0.020 0.020 mm HF in water (HF is a weak acid) HF in water (HF is a weak acid)

a)a) Which would have the same boiling point as Which would have the same boiling point as 0.040 m C0.040 m C66HH1212OO66 in water? in water?a)a) Which solution would have the highest vapor Which solution would have the highest vapor

pressure at 28pressure at 28ooC?C?b)b) Which solution would have the largest Which solution would have the largest

freezing point depression? freezing point depression?

Properties of Properties of Electrolyte Solutions Electrolyte Solutions (continued)(continued) From the following:From the following:

pure waterpure water0.01 0.01 mm C C1212HH2222OO1111 in water in water0.01 0.01 mm NaCl in water NaCl in water0.01 0.01 mm CaCl CaCl22 in water in water

Choose the one with theChoose the one with thea)a) Highest freezing pointHighest freezing pointb)b) Lowest freezing pointLowest freezing pointc)c) Highest boiling pointHighest boiling pointd)d) Lowest boiling pointLowest boiling pointe)e) Highest vapor pressureHighest vapor pressure

Solving Problems Solving Problems Using the van’t Hoff Using the van’t Hoff Factor?Factor? Calculate the freezing point and Calculate the freezing point and

the boiling point of each of the the boiling point of each of the following aqueous solutions.following aqueous solutions.a) 0.050 a) 0.050 mm MgCl MgCl22b) 0.050 b) 0.050 mm FeCl FeCl33

Osmotic PressureOsmotic Pressure Osmosis is the passage of a solvent Osmosis is the passage of a solvent

through a semi-permeable membrane.through a semi-permeable membrane. Osmotic Pressure is the minimum Osmotic Pressure is the minimum

pressure that stops osmosis.pressure that stops osmosis. The equation for osmotic pressure isThe equation for osmotic pressure is

ππ = iMRT = iMRT ππ is the pressure in atm is the pressure in atm MM is the molarity of the solution is the molarity of the solution R = 0.08206 LR = 0.08206 L.. atm/K atm/K.. mol mol T is the Kelvin temperatureT is the Kelvin temperature

Calculating Osmotic Calculating Osmotic PressurePressure To determine the molar mass of a To determine the molar mass of a

certain protein, .00100 g of it was certain protein, .00100 g of it was dissolved in enough water to make 1.00 dissolved in enough water to make 1.00 mL of solution. The osmotic pressure mL of solution. The osmotic pressure was found to be 1.12 torr at 25.0was found to be 1.12 torr at 25.0ooC. C. Calculate the molar mass of the protein.Calculate the molar mass of the protein.

What concentration of NaCl in water is What concentration of NaCl in water is needed to produce an aqueous solution needed to produce an aqueous solution isotonic with blood (isotonic with blood (ππ = 7.70 atm at 25 = 7.70 atm at 25ooC)?C)?

Calculating Osmotic Calculating Osmotic PressurePressure What osmotic pressure would What osmotic pressure would

50.0 g of sucrose in 117 g of 50.0 g of sucrose in 117 g of water exhibit at 25water exhibit at 25ooC? The C? The density of this solution is 1.34 density of this solution is 1.34 g/mL.g/mL.