1

Properties of Solutions

Chapter 11

2

Overview

Introduce student to solution composition and energy of solution formation.

Factor affecting solubilities will be discussed: structure, pressure and temperature effects.

Vapor pressure of solutions, boiling point, freezing point affected by solute addition.

Colligative properties of electrolyte solutions and colloids.

3

A solution is a homogenous mixture of 2 or more substances

The solute is(are) the substance(s) present in the smaller amount(s)

The solvent is the substance present in the larger amount

4

A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.

An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature.

A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature.

Sodium acetate crystals rapidly form when a seed crystal isadded to a supersaturated solution of sodium acetate.

5

Solution Composition

1. Molarity (M) =

2. Mass (weight) percent =

3. Mole fraction (A) =

4. Molality (m) =

moles of soluteliters of solution

mass of solutemass of solution

100%

molestotal moles in solution

A

moles of solutekilograms of solvent

6

Concentration UnitsThe concentration of a solution is the amount of solute present in a given quantity of solvent or solution.

Percent by Mass

% by mass = x 100%mass of solutemass of solute + mass of solvent

= x 100%mass of solutemass of solution

Mole Fraction (X)

XA = moles of A

sum of moles of all components

7

Concentration Units Continued

M =moles of solute

liters of solution

Molarity (M)

Molality (m)

m =moles of solute

mass of solvent (kg)

8

N =Number of equivalent

liters of solution

Normality (N)

Acid-Base reaction: is the amount needed to accept one mole of H+

Number of equivalent

=mass

Equivalent massx

1

V

Equivalent mass of H2SO4 = MM

2

Equivalent mass of Ca(OH)2 = MM

2

9

Redox reaction : is the amount needed to accept exactly one mole e-

MnO4- + 5e- + 8H+ Mn2+ + 4H2O

Equivalent mass of KMnO4 = MM

5

10

11

What is the molality of a 5.86 M ethanol (C2H5OH) solution whose density is 0.927 g/mL?

m =moles of solute

mass of solvent (kg)M =

moles of solute

liters of solution

Assume 1 L of solution:5.86 moles ethanol = 270 g ethanol927 g of solution (1000 mL x 0.927 g/mL)

mass of solvent = mass of solution – mass of solute

= 927 g – 270 g = 657 g = 0.657 kg

m =moles of solute

mass of solvent (kg)=

5.86 moles C2H5OH

0.657 kg solvent= 8.92 m

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Steps in Solution Formation

Step 1 - Expanding the solute (endothermic)

Step 2 - Expanding the solvent (endothermic)

Step 3 - Allowing the solute and solvent to interact to form a solution (exothermic)

Hsoln = Hstep 1 + Hstep 2 + Hstep 3

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The formation of a liquid solution can be divided into three steps: (1) expanding the solute, (2) expanding the solvent, and (3)

combining the expanded solute and solvent to form the solution.

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H < 0 ExothermicSolution will occur

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The driving factor that favor a process of solution formation is an increase in disorder

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Factor Affecting Solubility

1. Structure

2. Pressure

3. Temperature

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“like dissolves like”

Two substances with similar intermolecular forces are likely to be soluble in each other.

• non-polar molecules are soluble in non-polar solvents

CCl4 in C6H6

• polar molecules are soluble in polar solvents

C2H5OH in H2O

• ionic compounds are more soluble in polar solvents

NaCl in H2O or NH3 (l)

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The molecular structures of (a) vitamin A (nonpolar, fat-soluble) and (b) vitamin C (polar, water-soluble). The circles in the

structural formulas indicate polar bonds. Note that vitamin C contains far more polar bonds than vitamin A.

Fat Soluble

Hydrophobic

Water Soluble

Hydrophilic

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Pressure Effects

• Pressure has little effect on solids and liquids.

• It increases the solubility of gases.

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(a) A gaseous solute in equilibrium with a solution. (b) The piston is pushed in, increasing the pressure of the gas and number of gas molecules per unit volume. This causes an increase in the rate at which the gas enters the solution, so the concentration of dissolved gas increases. (c) The greater gas concentration in the solution causes an

increase in the rate of escape. A new equilibrium is reached.

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Henry’s Law

P = kC

P = partial pressure of gaseous solute above the solution

C = concentration of dissolved gask = a constant

The amount of a gas dissolved in a solution is The amount of a gas dissolved in a solution is directly proportional to the pressure of the gas directly proportional to the pressure of the gas above the solution.above the solution.

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Henry’s Law Applied for

• Dilute solutions

• Gases that do not dissociate or react with solvent:– O2/water Applied

– HCl/water Is not applied

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Temperature Effect on Gases

The solubilities of several gases in water as a function of temperature at a constant pressure of 1 atm of gas above the solution.

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The solubilities of several solids as a function of temperature.

Temperature Effect on Gases

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The Vapor Pressure of Solutions

• Solutions have different physical properties from pure solvent.

• Solutions of nonvolatile solutes differ from solutions of volatile solvents.

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An aqueous solution and pure water in a closed environment. (a) Initial stage. (b) After a period of time,

the water is transferred to the solution.

Vapor pressure of pure water is higher VP of solution is lower

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Raoult’s Law

Psoln = solvent Psolvent

Psoln = vapor pressure of the solution

solvent = mole fraction of the solvent

Psolvent = vapor pressure of the pure solvent

The presence of a The presence of a nonvolatilenonvolatile solute solute lowerslowers the vapor pressure of a solvent.the vapor pressure of a solvent.

solvent =Moles of solvents

Moles of solvent + Moles of solute

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Note

• Solutions that obey Raoult’s Law are called Ideal Solutions.

• Can be used to determine the molar mass of unknown.

• For ionic compounds you should multiply by the total number of ions per molecule

• e.g. Na2SO4 n = 3 x Na2SO4

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For a solution that obeys Raoult's law, a plot of Psoln versus xsolvent

gives a straight line.

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Non-Ideal Solutions

When a solution contains two volatile components, both contribute to the total vapor pressure.

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PA = XA P A0

PB = XB P B0

PT = PA + PB

PT = XA P A0 + XB P B

0

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(a) ideal liquid-liquid solution by Raoult's law. (b) This solution shows a positive deviation from Raoult's law. (c) This solution

shows a negative deviation from Raoult's law.

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PT is greater thanpredicted by Raoults’s law

PT is less thanpredicted by Raoults’s law

ForceA-B

ForceA-A

ForceB-B< &

ForceA-B

ForceA-A

ForceB-B> &

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Colligative Properties of Non-Electrolyte Solutions

Depend only on the number, not on the identity, of the solute particles in an ideal solution.

Boiling point elevation Freezing point depression Osmotic pressure

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Boiling Point Elevation

A nonvolatile solute elevates the boiling point of the solvent.

T = Kbmsolute

Kb = molal boiling point elevation constant

m = molality of the solute

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Boiling-Point Elevation

Tb = Tb – T b0

Tb > T b0 Tb > 0

T b is the boiling point of the pure solvent

0

T b is the boiling point of the solution

Tb = Kb m

m is the molality of the solution

Kb is the molal boiling-point elevation constant (0C/m)

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Freezing Point Depression

A nonvolatile solute depresses the freezing point of the solvent.

T = Kfmsolute

Kf = molal freezing point depression constant

m = molality of the solute

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Freezing-Point Depression

Tf = T f – Tf0

T f > Tf0 Tf > 0

T f is the freezing point of the pure solvent

0

T f is the freezing point of the solution

Tf = Kf m

m is the molality of the solution

Kf is the molal freezing-point depression constant (0C/m)

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Osmotic Pressure

Osmosis: The flow of solvent into the solution through the semipermeable membrane.

Osmotic Pressure: The excess hydrostatic pressure on the solution compared to the pure solvent.

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Osmotic Pressure ()

Osmosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one.

A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules.

Osmotic pressure () is the pressure required to stop osmosis.

= MRT

M is the molarity of the solution

R is the gas constant

T is the temperature (in K)

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A tube with a bulb on the end that is covered by a semipermeable membrane.

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The normal flow of solvent into the solution (osmosis) can be prevented by applying an external pressure to the solution. The minimum pressure required to stop the osmosis is equal to the osmotic pressure of the solution.

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(a) A pure solvent and its solution (containing a nonvolatile solute) are separated by a semipermeable membrane through which solvent molecules

(blue) can pass but solute molecules (green) cannot. The rate of solvent transfer is greater from solvent to solution than from solution to solvent. (b) The system at equilibrium, where the rate of solvent transfer is the same in both directions.

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If the external pressure is larger than the osmotic pressure, reverse osmosis occurs.

One application is desalination of seawater.

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Reverse osmosis.

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A cell in an:

isotonicSolution

(identical )

hypotonicSolution

(water in)

hypertonicSolution

(water out)

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Colligative Properties of Electrolyte Solutions

T = imK

= iMRT

i = moles of particles in solution

moles of solute dissolved

van’t Hoff factor, “van’t Hoff factor, “ii”, relates to the number of ”, relates to the number of ions per formula unit.ions per formula unit.

NaCl = 2, KNaCl = 2, K22SOSO44 = 3 (Theoretically) = 3 (Theoretically)

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Boiling-Point Elevation Tb = i Kb m

Freezing-Point Depression Tf = i Kf m

Osmotic Pressure () = iMRT

Colligative Properties of Electrolyte Solutions

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In an aqueous solution a few ions aggregate, forming ion pairs that

behave as a unit: Ion Pairing

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Colloids

Colloidal Dispersion (colloid): A suspension of tiny particles in some medium.

aerosols, foams, emulsions, sols

Coagulation: The addition of an electrolyte, causing destruction of a colloid.

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A representation of two colloidal particles.

The opposing charge repel and prevent precipitation

The destruction of colloids is called coagulation, achieved by1. Increasing temperature where colliding at higher veloicities

to penetrate the ion barriers and aggregate.2. Adding electrolytes to neutralize ion layers, this is why clay

deposits where rivers reach the oceans.

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A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance.

Colloid versus solution

• colloidal particles are much larger than solute molecules

• colloidal suspension is not as homogeneous as a solution

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The Cleansing Action of Soap

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The Cottrell precipitator installed in a smokestack. The charged plates attract

the colloidal particles because of their ion layers and thus remove them from the smoke.

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QUESTIONWhat is the molality of a solution of 50.0 g of propanol (CH3CH2CH2OH) in 152 mL water, if the density of water is 1.0 g/mL? 1) 5.47 m 2) 0.00547 m 3) 0.833 m 4) 0.183 m 5) None of these

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ANSWER1) 5.47 m Section 11.1 Solution Composition (p. 512) Using the density, the mass of the solution is found. Don’t forget that molality has units of kg of solvent and the mass of the solute must be subtracted from the calculated mass of solution.

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QUESTIONHow many milliliters of 18.4 M H2SO4 are needed to prepare 600.0 mL of 0.10 M H2SO4? 1) 1.8 mL 2) 2.7 mL 3) 3.3 mL 4) 4.0 mL 5) 4.6 mL

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ANSWER3) 3.3 mL Section 4.3 The Composition of Solutions (p. 145) Use the dilution equation remembering that M is mol/L not mol/mL.

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QUESTIONWhich of the following concentration measures will change in value as the temperature of a solution changes? 1) Mass percent 2) Mole fraction 3) Molality 4) Molarity 5) All of these

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ANSWER4) Molarity Section 11.1 Solution Composition (p. 512) Molarity is moles per liter of solution. The volume of a solution is temperature dependent. Generally, a solution will increase in volume as temperature increases.

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ANSWER (continued)Since the amount of solute does not change with temperature, the molar concentration of a solution decreases with increasing temperature.

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QUESTIONIf 2.00 g of helium gas and 4.00 g of oxygen gas are mixed together what is the mole fraction of helium in the solution? 1) 0.500 2) 0.333 3) 0.800 4) 0.200 5) 0.666

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ANSWER3) 0.800 Section 11.1 Solution Composition (p. 512) Remember to convert grams to moles before attempting to find the mole fraction.

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QUESTION

Which of the following favors the solubility of an ionic solid in a liquid solvent? 1) A large magnitude of the solvation energy of

the ions 2) A small magnitude of the lattice energy of

the solute 3) A large polarity of the solvent 4) All of these 5) None of these

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ANSWER4) All of these Section 11.2 The Energies of Solution Formation (p. 516) Nonpolar compounds will have little attraction to ions and will be poor solvents for ionic compounds.

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QUESTIONWhich of the following chemical or physical changes is an endothermic process? 1) The evaporation of water 2) The combustion of gasoline 3) The mixing of sulfuric acid and water 4) The freezing of water 5) None of these

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ANSWER1) The evaporation of water Section 11.2 The Energies of Solution Formation (p. 517) Endo meaning “in” or “inside” indicates that endothermic is the flow of heat into a system.

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QUESTIONWhich statement about hydrogen bonding is true?

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QUESTION (continued)

1) Hydrogen bonding is the intermolecular attractive forces between two hydrogen atoms in solution.

2) The hydrogen bonding capabilities of water molecules cause CH3CH2CH2CH3 to be more soluble in water than CH3OH.

3) Hydrogen bonding of solvent molecules with a solute will not affect the solubility of the solute.

4) Hydrogen bonding interactions between molecules are stronger than the covalent bonds within the molecule.

5) Hydrogen bonding arises from the dipole moment created by the unequal sharing of electrons within certain covalent bonds within a molecule.

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ANSWER5) Hydrogen bonding arises from the dipole

moment created by the unequal sharing of electrons within certain covalent bonds within a molecule.

Section 11.3 Factors Affecting Solubility (p. 519) Hydrogen bonding is a dipole-dipole interaction, but one of such magnitude that it receives its own classification.

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QUESTIONThe lattice energy of NaI is 686 kJ/mol and its heat of solution is –7.6 kJ/mol. Calculate the hydration of energy of NaI(s). 1) +15.2 2) –678 3) –694 4) +678 5) +694

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ANSWER3) –694 Section 11.2 The Energies of Solution Formation (p. 517) The hydration energy is needed to overcome the lattice energy, breaking the ionic bonds to loosen the ions in the crystal.

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QUESTIONA correct statement of Henry’s law is: 1) the concentration of a gas in solution is

inversely proportional to temperature. 2) the concentration of a gas in solution is directly

proportional to the mole fraction of solvent. 3) the concentration of a gas in solution is

independent of pressure. 4) the concentration of a gas in a solution is

inversely proportional to pressure. 5) none of these

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ANSWER5) none of these Section 11.3 Factors Affecting Solubility (p. 521) Henry’s law states that the amount of a gas dissolved in a solution is directly proportional to the pressure of the gas above the solution.

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QUESTIONA salt solution sits in an open beaker. Assuming constant temperature and pressure, the vapor pressure of the solution: 1) increases over time. 2) decreases over time. 3) stays the same over time. 4) Need to know which salt is in the solution to

answer this. 5) Need to know the temperature and pressure

to answer this.

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ANSWER2) decreases over time. Section 11.4 The Vapor Pressures of Solutions (p. 525) The concentration of the solution increases as the water evaporates. The higher the concentration of salt, the lower the vapor pressure.

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QUESTIONA solution of two liquids, A and B, shows negative deviation from Raoult’s law. This means that:

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QUESTION (continued)

1) the molecules of A interact strongly with other A-type molecules.

2) the two liquids have a positive heat of solution.

3) molecules of A interact weakly, if at all, with B molecules.

4) the molecules of A hinder the strong interaction between B molecules.

5) molecules of A interact more strongly with B than A with A or B with B.

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ANSWER5) molecules of A interact more strongly with B than A

with A or B with B. Section 11.4 The Vapor Pressures of Solutions (p. 526) Raoult’s Law depends on solutions being ideal, that is, the molecules of A and molecules of B do not interact. Many solutions have near ideal behavior, but the solute(s) and solvent of every solution interact to some degree.

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QUESTIONA liquid-liquid solution is called an ideal solution if:

a. it obeys PV = nRT. b. it obeys Raoult’s law. c. solute-solute, solvent-solvent, and

solute-solvent interactions are very similar.

d. solute-solute, solvent-solvent, and solute-solvent interactions are quite different.

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QUESTION (continued)

1) a, b, c 2) a, b, d 3) b, c 4) b, d 5) a, b, c

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ANSWER3) b, c Section 11.4 The Vapor Pressures of Solutions (p. 529) PV = nRT applies only to gases.

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QUESTIONAll of the following are colligative properties except: 1) osmotic pressure. 2) boiling point elevation. 3) freezing point depression. 4) density elevation. 5) none of these.

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ANSWER4) density elevation. Section 11.5 Boiling-Point Elevation and Freezing-Point Depression (p. 531) Density elevation is not a term in common chemical use.

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QUESTIONWhich of the following will cause the calculated molar mass of a compound determined by the freezing point depression method to be greater than the true molar mass?

89

QUESTION (continued)

1) Water gets into the solvent after the freezing point of the pure solvent is determined.

2) Some of the solute molecules break apart. 3) The mass of solvent is smaller than

determined from the weighing. 4) While adding the solute, some was spilled

on the lab bench. 5) All of these

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ANSWER4) While adding the solute, some was spilled on

the lab bench. Section 11.5 Boiling-Point Elevation and Freezing-Point Depression (p. 533) Aside from the possible health hazards, spilling chemicals in the lab will generally be disastrous to any quantitative experiment.

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QUESTIONA solute added to a solvent raises the boiling point of the solution because:

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QUESTION (continued)

1) the temperature to cause boiling must be great enough to boil not only the solvent but also the solute.

2) the solute particles lower the solvent’s vapor pressure, thus requiring a higher temperature to cause boiling.

3) the solute particles raise the solvent’s vapor pressure, thus requiring a higher temperature to cause boiling.

4) the solute increases the volume of the solution, and an increase in volume requires an increase in the temperature to reach the boiling point (derived from PV = nRT).

5) two of these are correct.

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ANSWER2) the solute particles lower the solvent’s vapor

pressure, thus requiring a higher temperature to cause boiling.

Section 11.5 Boiling-Point Elevation and Freezing-Point Depression (p. 532) At the molecular level, solute molecules at the surface interfere with solvent molecules trying to reach the vapor phase. Extra energy is needed to escape.

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QUESTIONA cucumber is placed in a concentrated salt solution. What will most likely happen? 1) Water will flow from the cucumber to the

solution. 2) Water will flow from the solution to the

cucumber. 3) Salt will flow into the cucumber. 4) Salt will precipitate out. 5) No change will occur.

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ANSWER1) Water will flow from the cucumber to the

solution. Section 11.6 Osmotic Pressure (p. 536) Water from the cucumber flows out in an attempt to bring the concentrations of ions to the same level inside and outside of the cucumber.

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QUESTIONSolutions that have identical osmotic pressures are called __________ solutions. 1) hypertonic 2) isotonic 3) hypotonic 4) hemolytic 5) dyalitic

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ANSWER2) isotonic Section 11.6 Osmotic Pressure (p. 538) Organisms attempt to keep their cells and their surroundings in an isotonic state. This state is the most beneficial to cell function.

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QUESTIONThe most likely reason for colloidal dispersion is __________. 1) the Tyndall effect 2) coagulation 3) precipitation 4) emulsion formation 5) electrostatic repulsion

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ANSWER5) electrostatic repulsion Section 11.8 Colloids (p. 543) The electrostatic repulsion arises from the layers of ions that form around the colloidal particles.

100

Chapter 11

Properties ofProperties ofSolutionsSolutions

101

QUESTIONWhat is the molality of a solution of 50.0 g of propanol (CH3CH2CH2OH) in 152 mL water, if the density of water is 1.0 g/mL? 1) 5.47 m 2) 0.00547 m 3) 0.833 m 4) 0.183 m 5) None of these

102

ANSWER1) 5.47 m Section 11.1 Solution Composition (p. 512) Using the density, the mass of the solution is found. Don’t forget that molality has units of kg of solvent and the mass of the solute must be subtracted from the calculated mass of solution.

103

QUESTIONHow many milliliters of 18.4 M H2SO4 are needed to prepare 600.0 mL of 0.10 M H2SO4? 1) 1.8 mL 2) 2.7 mL 3) 3.3 mL 4) 4.0 mL 5) 4.6 mL

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ANSWER3) 3.3 mL Section 4.3 The Composition of Solutions (p. 145) Use the dilution equation remembering that M is mol/L not mol/mL.

105

QUESTIONWhich of the following concentration measures will change in value as the temperature of a solution changes? 1) Mass percent 2) Mole fraction 3) Molality 4) Molarity 5) All of these

106

ANSWER4) Molarity Section 11.1 Solution Composition (p. 512) Molarity is moles per liter of solution. The volume of a solution is temperature dependent. Generally, a solution will increase in volume as temperature increases.

107

ANSWER (continued)Since the amount of solute does not change with temperature, the molar concentration of a solution decreases with increasing temperature.

108

QUESTIONIf 2.00 g of helium gas and 4.00 g of oxygen gas are mixed together what is the mole fraction of helium in the solution? 1) 0.500 2) 0.333 3) 0.800 4) 0.200 5) 0.666

109

ANSWER3) 0.800 Section 11.1 Solution Composition (p. 512) Remember to convert grams to moles before attempting to find the mole fraction.

110

QUESTION

Which of the following favors the solubility of an ionic solid in a liquid solvent? 1) A large magnitude of the solvation energy of

the ions 2) A small magnitude of the lattice energy of

the solute 3) A large polarity of the solvent 4) All of these 5) None of these

111

ANSWER4) All of these Section 11.2 The Energies of Solution Formation (p. 516) Nonpolar compounds will have little attraction to ions and will be poor solvents for ionic compounds.

112

QUESTIONWhich of the following chemical or physical changes is an endothermic process? 1) The evaporation of water 2) The combustion of gasoline 3) The mixing of sulfuric acid and water 4) The freezing of water 5) None of these

113

ANSWER1) The evaporation of water Section 11.2 The Energies of Solution Formation (p. 517) Endo meaning “in” or “inside” indicates that endothermic is the flow of heat into a system.

114

QUESTIONWhich statement about hydrogen bonding is true?

115

QUESTION (continued)

1) Hydrogen bonding is the intermolecular attractive forces between two hydrogen atoms in solution.

2) The hydrogen bonding capabilities of water molecules cause CH3CH2CH2CH3 to be more soluble in water than CH3OH.

3) Hydrogen bonding of solvent molecules with a solute will not affect the solubility of the solute.

4) Hydrogen bonding interactions between molecules are stronger than the covalent bonds within the molecule.

5) Hydrogen bonding arises from the dipole moment created by the unequal sharing of electrons within certain covalent bonds within a molecule.

116

ANSWER5) Hydrogen bonding arises from the dipole

moment created by the unequal sharing of electrons within certain covalent bonds within a molecule.

Section 11.3 Factors Affecting Solubility (p. 519) Hydrogen bonding is a dipole-dipole interaction, but one of such magnitude that it receives its own classification.

117

QUESTIONThe lattice energy of NaI is 686 kJ/mol and its heat of solution is –7.6 kJ/mol. Calculate the hydration of energy of NaI(s). 1) +15.2 2) –678 3) –694 4) +678 5) +694

118

ANSWER3) –694 Section 11.2 The Energies of Solution Formation (p. 517) The hydration energy is needed to overcome the lattice energy, breaking the ionic bonds to loosen the ions in the crystal.

119

QUESTIONA correct statement of Henry’s law is: 1) the concentration of a gas in solution is

inversely proportional to temperature. 2) the concentration of a gas in solution is directly

proportional to the mole fraction of solvent. 3) the concentration of a gas in solution is

independent of pressure. 4) the concentration of a gas in a solution is

inversely proportional to pressure. 5) none of these

120

ANSWER5) none of these Section 11.3 Factors Affecting Solubility (p. 521) Henry’s law states that the amount of a gas dissolved in a solution is directly proportional to the pressure of the gas above the solution.

121

QUESTIONA salt solution sits in an open beaker. Assuming constant temperature and pressure, the vapor pressure of the solution: 1) increases over time. 2) decreases over time. 3) stays the same over time. 4) Need to know which salt is in the solution to

answer this. 5) Need to know the temperature and pressure

to answer this.

122

ANSWER2) decreases over time. Section 11.4 The Vapor Pressures of Solutions (p. 525) The concentration of the solution increases as the water evaporates. The higher the concentration of salt, the lower the vapor pressure.

123

QUESTIONA solution of two liquids, A and B, shows negative deviation from Raoult’s law. This means that:

124

QUESTION (continued)

1) the molecules of A interact strongly with other A-type molecules.

2) the two liquids have a positive heat of solution.

3) molecules of A interact weakly, if at all, with B molecules.

4) the molecules of A hinder the strong interaction between B molecules.

5) molecules of A interact more strongly with B than A with A or B with B.

125

ANSWER5) molecules of A interact more strongly with B than A

with A or B with B. Section 11.4 The Vapor Pressures of Solutions (p. 526) Raoult’s Law depends on solutions being ideal, that is, the molecules of A and molecules of B do not interact. Many solutions have near ideal behavior, but the solute(s) and solvent of every solution interact to some degree.

126

QUESTIONA liquid-liquid solution is called an ideal solution if:

a. it obeys PV = nRT. b. it obeys Raoult’s law. c. solute-solute, solvent-solvent, and

solute-solvent interactions are very similar.

d. solute-solute, solvent-solvent, and solute-solvent interactions are quite different.

127

QUESTION (continued)

1) a, b, c 2) a, b, d 3) b, c 4) b, d 5) a, b, c

128

ANSWER3) b, c Section 11.4 The Vapor Pressures of Solutions (p. 529) PV = nRT applies only to gases.

129

QUESTIONAll of the following are colligative properties except: 1) osmotic pressure. 2) boiling point elevation. 3) freezing point depression. 4) density elevation. 5) none of these.

130

ANSWER4) density elevation. Section 11.5 Boiling-Point Elevation and Freezing-Point Depression (p. 531) Density elevation is not a term in common chemical use.

131

QUESTIONWhich of the following will cause the calculated molar mass of a compound determined by the freezing point depression method to be greater than the true molar mass?

132

QUESTION (continued)

1) Water gets into the solvent after the freezing point of the pure solvent is determined.

2) Some of the solute molecules break apart. 3) The mass of solvent is smaller than

determined from the weighing. 4) While adding the solute, some was spilled

on the lab bench. 5) All of these

133

ANSWER4) While adding the solute, some was spilled on

the lab bench. Section 11.5 Boiling-Point Elevation and Freezing-Point Depression (p. 533) Aside from the possible health hazards, spilling chemicals in the lab will generally be disastrous to any quantitative experiment.

134

QUESTIONA solute added to a solvent raises the boiling point of the solution because:

135

QUESTION (continued)

1) the temperature to cause boiling must be great enough to boil not only the solvent but also the solute.

2) the solute particles lower the solvent’s vapor pressure, thus requiring a higher temperature to cause boiling.

3) the solute particles raise the solvent’s vapor pressure, thus requiring a higher temperature to cause boiling.

4) the solute increases the volume of the solution, and an increase in volume requires an increase in the temperature to reach the boiling point (derived from PV = nRT).

5) two of these are correct.

136

ANSWER2) the solute particles lower the solvent’s vapor

pressure, thus requiring a higher temperature to cause boiling.

Section 11.5 Boiling-Point Elevation and Freezing-Point Depression (p. 532) At the molecular level, solute molecules at the surface interfere with solvent molecules trying to reach the vapor phase. Extra energy is needed to escape.

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QUESTIONA cucumber is placed in a concentrated salt solution. What will most likely happen? 1) Water will flow from the cucumber to the

solution. 2) Water will flow from the solution to the

cucumber. 3) Salt will flow into the cucumber. 4) Salt will precipitate out. 5) No change will occur.

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ANSWER1) Water will flow from the cucumber to the

solution. Section 11.6 Osmotic Pressure (p. 536) Water from the cucumber flows out in an attempt to bring the concentrations of ions to the same level inside and outside of the cucumber.

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QUESTIONSolutions that have identical osmotic pressures are called __________ solutions. 1) hypertonic 2) isotonic 3) hypotonic 4) hemolytic 5) dyalitic

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ANSWER2) isotonic Section 11.6 Osmotic Pressure (p. 538) Organisms attempt to keep their cells and their surroundings in an isotonic state. This state is the most beneficial to cell function.

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QUESTIONThe most likely reason for colloidal dispersion is __________. 1) the Tyndall effect 2) coagulation 3) precipitation 4) emulsion formation 5) electrostatic repulsion

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ANSWER5) electrostatic repulsion Section 11.8 Colloids (p. 543) The electrostatic repulsion arises from the layers of ions that form around the colloidal particles.