chapter 13 properties of solutions
DESCRIPTION
Chapter 13 Properties of Solutions. 13.1 The Solution Process. Solutions. Solutions are homogeneous mixtures of two or more pure substances. In a solution, the solute is dispersed uniformly throughout the solvent (present in greatest amount). Solutions. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/1.jpg)
Chapter 13Properties of Solutions
![Page 2: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/2.jpg)
13.1 The Solution Process
![Page 3: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/3.jpg)
Solutions
Solutions are homogeneous mixtures of two or more pure substances.
In a solution, the solute is dispersed uniformly throughout the solvent (present in greatest amount).
![Page 4: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/4.jpg)
Solutions
The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles.
![Page 5: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/5.jpg)
How Does a Solution Form?
As a solution forms, the solvent pulls solute particles apart and surrounds, or solvates, them.
![Page 6: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/6.jpg)
How Does a Solution Form
If an ionic salt is soluble in water, it is because the ion-dipole interactions are strong enough to overcome the lattice energy of the salt crystal.
![Page 7: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/7.jpg)
Energy Changes in Solution Simply put, three
processes affect the energetics of solution: separation of solute
particles, separation of solvent
particles, new interactions between
solute and solvent.
![Page 8: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/8.jpg)
Energy Changes in Solution
The enthalpy change of the overall process depends on H for each of these steps.
![Page 9: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/9.jpg)
Why Do Endothermic Processes Occur?
Things do not tend to occur spontaneously (i.e., without outside intervention) unless the energy of the system is lowered.
![Page 10: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/10.jpg)
Why Do Endothermic Processes Occur?
Yet we know the in some processes, like the dissolution of NH4NO3 in water, heat is absorbed, not released.
![Page 11: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/11.jpg)
Enthalpy Is Only Part of the Picture
The reason is that increasing the disorder or randomness (known as entropy) of a system tends to lower the energy of the system.
![Page 12: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/12.jpg)
Enthalpy Is Only Part of the Picture
So even though enthalpy may increase, the overall energy of the system can still decrease if the system becomes more disordered.
![Page 13: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/13.jpg)
Student, Beware!
Just because a substance disappears when it comes in contact with a solvent, it doesn’t mean the substance dissolved.
Dissolution is a physical change — you can get back the original solute by evaporating the solvent.
If you can’t, the substance didn’t dissolve, it reacted.
![Page 14: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/14.jpg)
13.1 GIST
Why doesn’t NaCl dissolve in nonpolar solvents such as hexane, C6H14?
Label the following processes as exothermic or endothermic: Forming solvent-solute interactions Breaking solvent-solvent interactions
Silver chloride, AgCl, is essentially insoluble in water. Would you expect a significant change in entropy of the system when 10 g of AgCl is added to 500 mL of water?
![Page 15: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/15.jpg)
Sample Exercise 13.1
1) Water vapor reacts with excess solid sodium sulfate to form a hydrate:
Na2SO4(s) + 10 H2O(g) → Na2SO4●10H2O(s)
a) Does the system become more or less ordered in the process?
b) Does the entropy of the system increase or decrease?
![Page 16: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/16.jpg)
Practice
2) Does the entropy increase or decrease when the stopcock is opened allowing mixing of the two gases?
![Page 17: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/17.jpg)
13.2 Saturated Solutions and Solubility
![Page 18: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/18.jpg)
Types of Solutions
Saturated In a saturated solution,
the solvent holds as much solute as is possible at that temperature.
Dissolved solute is in dynamic equilibrium with solid solute particles.
![Page 19: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/19.jpg)
Types of Solutions
Unsaturated If a solution is
unsaturated, less solute than can dissolve in the solvent at that temperature is dissolved in the solvent.
![Page 20: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/20.jpg)
Types of Solutions
Supersaturated In supersaturated solutions, the solvent holds more
solute than is normally possible at that temperature. These solutions are unstable; crystallization can usually
be stimulated by adding a “seed crystal” or scratching the side of the flask.
p.535 GIST: Is a supersaturated solution of sodium acetate a stable equilibrium solution?
![Page 21: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/21.jpg)
13.3 Factors Affecting Solubility
![Page 22: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/22.jpg)
Factors Affecting Solubility
Chemists use the axiom “like dissolves like." Polar substances tend to dissolve in polar solvents. Nonpolar substances tend to dissolve in nonpolar solvents.
![Page 23: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/23.jpg)
Factors Affecting Solubility
The more similar the intermolecular attractions, the more likely one substance is to be soluble in another.
![Page 24: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/24.jpg)
Factors Affecting SolubilityGlucose (which has hydrogen bonding) is very soluble in water, while cyclohexane (which only has dispersion forces) is not.
p.538 GIST: Suppose the hydrogens on the OH groups in glucose were replaced with methyl groups, CH3. Would you expect the solubility of the resulting molecule to be higher than, lower than, or about the same as the solubility of glucose?
![Page 25: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/25.jpg)
Factors Affecting Solubility
Vitamin A is soluble in nonpolar compounds (like fats).
Vitamin C is soluble in water.
![Page 26: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/26.jpg)
Sample Exercise 13.2 Predicting Solubility Patterns
Predict whether each of the following substances is more likely to dissolve in the nonpolar solvent carbon tetrachloride (CCl4) or in water: C7H16, Na2SO4, HCl, and I2.
![Page 27: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/27.jpg)
Sample Exercise 13.2 Predicting Solubility Patterns
Arrange the following substances in order of increasing solubility in water:
Practice Exercise
![Page 28: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/28.jpg)
Gases in Solution
In general, the solubility of gases in water increases with increasing mass.
Larger molecules have stronger dispersion forces.
![Page 29: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/29.jpg)
Gases in Solution
The solubility of liquids and solids does not change appreciably with pressure.
The solubility of a gas in a liquid is directly proportional to its pressure.
![Page 30: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/30.jpg)
Henry’s Law
Sg = kPg
where Sg is the solubility of the
gas, k is the Henry’s Law
constant for that gas in that solvent, and
Pg is the partial pressure of the gas above the liquid.
![Page 31: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/31.jpg)
Exercise 13.13
1) Calculate the concentration of CO2 in a soft drink that is bottled with a partial pressure of CO2 of 4.0 atm over the liquid at 25ºC. The Henry’s law constant for CO2 in water at this temperature is 3.1 x 10-2 mol/L-atm.
2) Calculate the concentration of CO2 in a soft drink after the bottle is opened and equilibrates at 25ºC under a CO2 partial pressure of 3.0 x 10-4 atm.
![Page 32: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/32.jpg)
Temperature
Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.
![Page 33: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/33.jpg)
Temperature
The opposite is true of gases. Carbonated soft drinks
are more “bubbly” if stored in the refrigerator.
Warm lakes have less O2 dissolved in them than cool lakes.
![Page 34: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/34.jpg)
13.4 Ways of Expressing Concentration
![Page 35: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/35.jpg)
Mass Percentage
Mass % of A =mass of A in solutiontotal mass of solution
100
![Page 36: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/36.jpg)
Parts per Million andParts per Billion
ppm = mass of A in solutiontotal mass of solution
106
Parts per Million (ppm)
Parts per Billion (ppb)
ppb =mass of A in solutiontotal mass of solution
109
![Page 37: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/37.jpg)
Sample Exercise 13.4 Calculation of Mass-Related Concentrations
(a) Calculate the mass percentage of NaCl in a solution containing 1.50 g of NaCl in 50.0 g of water. (b) A commercial bleaching solution contains 3.62 mass % sodium hypochlorite, NaOCl. What is the mass of NaOCl in a bottle containing 2.50 kg of bleaching solution?
Practice Exercise
(a) A solution is made by dissolving 13.5 g of glucose (C6H12O6) in 0.100 kg of water. What is the mass percentage of solute in this solution? (b) A 2.5-g sample of groundwater was found to contain 5.4 µg of Zn2+. What is the concentration of Zn2+ in parts per million?
![Page 38: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/38.jpg)
moles of Atotal moles in solution
XA =
Mole Fraction (X)
In some applications, one needs the mole fraction of solvent, not solute — make sure you find the quantity you need!
![Page 39: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/39.jpg)
mol of soluteL of solution
M =
Molarity (M)
You will recall this concentration measure from Chapter 4.
Since volume is temperature-dependent, molarity can change with temperature.
![Page 40: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/40.jpg)
mol of solutekg of solvent
m =
Molality (m)
Since both moles and mass do not change with temperature, molality (unlike molarity) is not temperature-dependent.
![Page 41: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/41.jpg)
Changing Molarity to Molality
If we know the density of the solution, we can calculate the molality from the molarity and vice versa.
![Page 42: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/42.jpg)
Sample Exercise 13.5 Calculation of Molality
A solution is made by dissolving 4.35 g glucose (C6H12O6) in 25.0 mL of water at 25 °C. Calculate the molality of glucose in the solution. Water has a density of 1.00 g/mL.
![Page 43: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/43.jpg)
Practice
What is the molality of a solution made by dissolving 36.5 g of naphthalene (C10H8) in 425 g of toluene (C7H8)?
![Page 44: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/44.jpg)
Sample Exercise 13.6 Calculation of Mole Fraction and Molality
An aqueous solution of hydrochloric acid contains 36% HCl by mass. (a) Calculate the mole fraction of HCl in the solution. (b) Calculate the molality of HCl in the solution.
![Page 45: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/45.jpg)
Practice
1) A commercial bleach contains 3.62 mass % NaOCl in water. Calculate: A) the molality B) the mole fraction of NaOCl
![Page 46: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/46.jpg)
Sample Exercise 13.7 Calculation of Molality Using the Density of a Solution
A solution with a density of 0.876 g/mL contains 5.0 g of toluene (C7H8) and 225 g of benzene. Calculate the molarity of the solution.
![Page 47: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/47.jpg)
Practice
1) A solution containing equal masses of glycerol (C3H8O3) and water has a density of 1.10 g/mL. Calculate: A) The molality of glycerol B) The mole fraction of glycerol C) The molarity of glycerol in the solution
![Page 48: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/48.jpg)
13.5 Colligative Properties
![Page 49: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/49.jpg)
Colligative Properties Changes in colligative properties depend
only on the number of solute particles present, not on the identity of the solute particles.
Among colligative properties are Vapor pressure lowering Boiling point elevation Melting point depression Osmotic pressure
![Page 50: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/50.jpg)
Vapor Pressure
Because of solute-solvent intermolecular attraction, higher concentrations of nonvolatile solutes make it harder for solvent to escape to the vapor phase.
![Page 51: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/51.jpg)
Vapor Pressure
Therefore, the vapor pressure of a solution is lower than that of the pure solvent.
![Page 52: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/52.jpg)
Raoult’s Law
PA = XAPAwhere XA is the mole fraction of compound A, and
PA is the normal vapor pressure of A at that temperature.
NOTE: This is one of those times when you want to make sure you have the vapor pressure of the solvent.
![Page 53: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/53.jpg)
Sample Exercise 13.8 Calculation of Vapor-Pressure Lowering
Glycerin (C3H8O3) is a nonvolatile nonelectrolyte with a density of 1.26 g/mL at 25 °C. Calculate the vapor pressure at 25 °C of a solution made by adding 50.0 mL of glycerin to 500.0 mL of water. The vapor pressure of pure water at 25 °C is 23.8 torr (Appendix B), and its density is 1.00 g/mL.
![Page 54: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/54.jpg)
Practice
1) The vapor pressure of pure water at 110ºC is 1070 torr. A solution of ethylene glycol and water has a vapor pressure of 1.00 atm at 110ºC. Assuming that Raoult’s law is obeyed, what is the mole fraction of ethylene glycol in the solution?
P.547 GIST: Adding 1 mol of NaCl to 1 kg of water reduces the vapor pressure of water more than adding 1 mol of C6H12O6. Explain.
![Page 55: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/55.jpg)
Ideal Solutions Ideal solutions obey Raoult’s Law Real liquid-liquid solutions best approximate
ideal behavior when the solute concentration is low and when the solute and solvent have similar molecular sizes and similar types of intermolecular attractions.
If a solution is not ideal, the observed vapor pressure will either by higher or lower than predicted using Raoult’s Law
![Page 56: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/56.jpg)
Deviation from Raoult’s Law negative deviation
ex. acetone and water when solvent has special attraction to solute observed vapor pressure will be lower than
predicted
![Page 57: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/57.jpg)
Deviation from Raoult’s Law positive deviation
ex. ethanol and hexane when solvent has especially weak interactions
with solute observed vapor pressure will be higher than
predicted
![Page 58: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/58.jpg)
Volatile Solutions when both components are
volatile
where PA and PB are partial pressures
PA° and PB
° are vapor pressure of pure A and B
BBAABAtotal PPPPP
![Page 59: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/59.jpg)
A solution is prepared by mixing 5.81 g of acetone (C3H6O, molar mass = 58.1 g/mol) and 11.9 g of chloroform (HCCl3, molar mass = 119.4 g/mol). At 35oC, this solution has a total pressure of 260. torr. Is this an ideal solution? The vapor pressure of pure acetone and pure chloroform at 35oC are 345 torr and 293 torr respectively.
![Page 60: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/60.jpg)
Boiling Point Elevation a nonvolatile solute lowers the vapor pressure a higher T is required to reach the 1 atm of
pressure which defines boiling point a nonvolatile solute elevates the boiling point
of the solvent the amount of the elevation depends on
concentration of the solute
soluteb mKT p.549 GIST: An unknown solute dissolved in water causes the boiling point to increase by 0.51°C. Does this mean that the concentration of the solute is 1.0m?
![Page 61: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/61.jpg)
Freezing Point Depression vapor pressure of solid and liquid are equal at
freezing point nonvolatile solute lowers the vapor pressure so a
lower T is needed to decrease the vapor pressure to that of the solid
a nonvolatile solute depresses the freezing point of the solvent
the amount of the depression depends on concentration of the solute
solutef mKT
![Page 62: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/62.jpg)
![Page 63: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/63.jpg)
Boiling Point Elevation and Freezing Point Depression
Note that in both equations, T does not depend on what the solute is, but only on how many particles are dissolved.
Tb = Kb m
Tf = Kf m
![Page 64: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/64.jpg)
Example 1
18.00 g of glucose are added to 150.0 g of water. The boiling point constant is 0.51 C*kg/mol.
What is the boiling point of the solution?
![Page 65: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/65.jpg)
Example 2
What mass of C2H6O2 (M=62.1 g/mol) needs to be added to 10.0 L H2O to make a solution that freezes at -23.3°C?
density is 1.00 g/mL boiling point constant is
1.86°C*kg/mol
![Page 66: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/66.jpg)
Exercise 13.9
1) Automotive antifreeze consists of ethylene glycol (C2H6O2), a nonvolative nonelectrolyte. Calculate the boiling point and freezing point of a 25.0 mass % solution of ethylene glycol in water.
2) Calculate the freezing point of a solution containing 0.600 kg of CHCl3 and 42.0 g of eucalyptol (C10H18O), a fragrant substance found in the leaves of eucalyptus trees.
![Page 67: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/67.jpg)
Colligative Properties of Electrolytes
Since these properties depend on the number of particles dissolved, solutions of electrolytes (which dissociate in solution) should show greater changes than those of nonelectrolytes.
![Page 68: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/68.jpg)
Colligative Properties of Electrolytes
However, a 1M solution of NaCl does not show twice the change in freezing point that a 1M solution of methanol does.
![Page 69: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/69.jpg)
van’t Hoff Factor
One mole of NaCl in water does not really give rise to two moles of ions.
![Page 70: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/70.jpg)
van’t Hoff Factor
Some Na+ and Cl- reassociate for a short time, so the true concentration of particles is somewhat less than two times the concentration of NaCl.
![Page 71: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/71.jpg)
van’t Hoff Factor
Reassociation is more likely at higher concentration.
Therefore, the number of particles present is concentration-dependent.
![Page 72: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/72.jpg)
van’t Hoff Factor
We modify the previous equations by multiplying by the van’t Hoff factor, i.
Tf = Kf m i
![Page 73: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/73.jpg)
Exercise 13.10
1) List the following aqueous solutions in order of their expected freezing point: 0.050m CaCl2, 0.15m NaCl, 0.10m HCl, 0.050m HC2H3O2, and 0.10m C12H22O11.
2) Which of the following solutes will produce the largest increase in boiling point upon addition ot 1 kg of water: 1 mol Co(NO3)2, 2 mol KCl, or 3 mol of ethylene glycol (C2H6O2)?
![Page 74: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/74.jpg)
Osmosis
Some substances form semipermeable membranes, allowing some smaller particles to pass through, but blocking other larger particles.
In biological systems, most semipermeable membranes allow water to pass through, but solutes are not free to do so.
![Page 75: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/75.jpg)
Semi-permeable Membrane a partition that allows solvent particles to pass
through but not solute particles separates a solution and a pure solvent
![Page 76: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/76.jpg)
Osmosis the flow of solvent through a semi-
permeable membrane when the system has reached
equilibrium, the water levels are different since there is greater hydrostatic pressure in a solution
![Page 77: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/77.jpg)
Osmosis
In osmosis, there is net movement of solvent from the area of higher solvent concentration (lower solute concentration) to the are of lower solvent concentration (higher solute concentration).
![Page 78: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/78.jpg)
Osmotic Pressure
The pressure required to stop osmosis, known as osmotic pressure, , is
nV
= ( )RT = MRT
where M is the molarity of the solution.
If the osmotic pressure is the same on both sides of a membrane (i.e., the concentrations are the same), the solutions are isotonic.
![Page 79: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/79.jpg)
Osmosis in Blood Cells
If the solute concentration outside the cell is greater than that inside the cell, the solution is hypertonic.
Water will flow out of the cell, and crenation results.
![Page 80: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/80.jpg)
Osmosis in Cells
If the solute concentration outside the cell is less than that inside the cell, the solution is hypotonic.
Water will flow into the cell, and hemolysis results.
![Page 81: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/81.jpg)
Sample Exercise 13.11 Calculations Involving Osmotic Pressure
The average osmotic pressure of blood is 7.7 atm at 25 °C. What molarity of glucose (C6H12O6) will be isotonic with blood?
![Page 82: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/82.jpg)
Practice
What is the osmotic pressure at 20 °C of a 0.0020 M sucrose (C12H22O11) solution?
P.533 GIST: Of two KBr solutions, one is 0.5m and the other is 0.20m, which is hypotonic with respect to the other?
![Page 83: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/83.jpg)
Example 3
When 1.00x10-3 g of a protein is mixed with water to make 1.00 mL of solution, the osmotic pressure is 1.12 torr at 25.0°C.
Find the molar mass of this protein.
![Page 84: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/84.jpg)
Sample Exercise 13.12 Molar Mass for Freezing-Point Depression
A solution of an unknown nonvolatile nonelectrolyte was prepared by dissolving 0.250 g of the substance in 40.0 g of CCl4. The boiling point of the resultant solution was 0.357 °C higher than that of the pure solvent. Calculate the molar mass of the solute.
![Page 85: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/85.jpg)
Sample Exercise 13.12 Molar Mass for Freezing-Point Depression
Camphor (C10H16O) melts at 179.8 °C, and it has a particularly large freezing-point-depression constant, Kf = 40.0 °C/m. When 0.186 g of an organic substance of unknown molar mass is dissolved in 22.01 g of liquid camphor, the freezing point of the mixture is found to be 176.7 °C. What is the molar mass of the solute?
Practice Exercise
![Page 86: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/86.jpg)
Sample Exercise 13.13 Molar Mass from Osmotic Pressure
The osmotic pressure of an aqueous solution of a certain protein was measured to determine the protein’s molar mass. The solution contained 3.50 mg of protein dissolved in sufficient water to form 5.00 mL of solution. The osmotic pressure of the solution at 25 °C was found to be 1.54 torr. Treating the protein as a nonelectrolyte, calculate its molar mass.
![Page 87: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/87.jpg)
Practice
A sample of 2.05 g of polystyrene of uniform polymer chain length was dissolved in enough toluene to form 0.100 L of solution. The osmotic pressure of this solution was found to be 1.21 kPa at 25ºC. Calculate the molar mass of polystyrene.
![Page 88: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/88.jpg)
13.6 Colloids
![Page 89: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/89.jpg)
Colloids
Suspensions of particles larger than individual ions or molecules, but too small to be settled out by gravity are called colloids.
![Page 90: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/90.jpg)
Tyndall Effect
Colloidal suspensions can scatter rays of light.
This phenomenon is known as the Tyndall effect.
![Page 91: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/91.jpg)
Colloids in Biological Systems
Some molecules have a polar, hydrophilic (water-loving) end and a non-polar, hydrophobic (water-hating) end.
![Page 92: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/92.jpg)
Colloids in Biological Systems
These molecules can aid in the emulsification of fats and oils in aqueous solutions.
![Page 93: Chapter 13 Properties of Solutions](https://reader036.vdocuments.us/reader036/viewer/2022081800/5681556d550346895dc33a57/html5/thumbnails/93.jpg)
Sample Integrative Exercise Putting Concepts Together
A 0.100-L solution is made by dissolving 0.441 g of CaCl2(s) in water. (a) Calculate the osmotic pressure of this solution at 27 °C, assuming that it is completely dissociated into its component ions. (b) The measured osmotic pressure of this solution is 2.56 atm at 27 °C. Explain why it is less than the value calculated in (a), and calculate the van’t Hoff factor, i, for the solute in this solution. (See the “A Closer Look” box on Colligative Properties of Electrolyte Solutions in Section 13.5.) (c) The enthalpy of solution for CaCl2 is ΔH = –81.3 kJ/mol. If the final temperature of the solution is 27 °C, what was its initial temperature? (Assume that the density of the solution is 1.00 g/mL, that its specific heat is 4.18 J/g-K, and that the solution loses no heat to its surroundings.)