Chemistry
Colligative Properties
Colligative properties are physical properties of solutions that depend on the concentration of solute particles but not on their identity. These properties include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure. They are important in many industrial and biological processes.
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12 Key excerpts on "Colligative Properties"
- Frank R. Foulkes(Author)
- 2012(Publication Date)
- CRC Press(Publisher)
These changes in the physical properties of solutions, and the extent of the changes, depend (approximately) only on the number of solute particles dis-solved in the solvent, and not on the actual identity of the solute. Such properties are called Colligative Properties and are related to each other. Thus, once one––such as the in-crease in the boiling point of the solution––has been measured, all the others––such as the decrease in the freezing point or the lowering of the vapor pressure––can be calculated. All colligative behavior most closely obeys the ideal equations as the concentration of the solute approaches zero; i.e., when the solute particles are so far apart that there is negligible interaction among them to give rise to “nonideal” behavior. 2. The lowering of the vapor pressure (vapor pressure depression) by a non-volatile solute A is given by Concentration (m g Buna S-3 in 100 mL) 6 z (cm) 730 3.57 547.5 2.26 365 1.17 182.5 0.43 Colligative Properties 18-13 6 P P W • = x A where P W • is the vapor pressure of the pure solvent, P W is the vapor pressure of the solu-tion, 6 P = P W • – P W is the lowering of the vapor pressure, and x A is the mole fraction of the solute in the solution. Note : If the solute dissociates into particles, it is the total number of particles that must be used to calculate the “effective” mole fraction of the solute. 3. The boiling point elevation 6 T b and freezing point depression | 6 T f | are given, respectively, by 6 T b = K m b i and | 6 T f | = K m f i where m i is the “effective” molality of the solute, K b is the boiling point elevation constant (the ebullioscopic constant ) and K f is the freezing point depression constant (the cryoscopic constant ). 4. The origin of all the Colligative Properties is the lowering of the chemical potential of the solvent by the presence of a solute.
eBook - PDF- Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2019(Publication Date)
- Openstax(Publisher)
There are a few solution properties, however, that depend only upon the total concentration of solute species, regardless of their identities. These Colligative Properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. This small set of properties is of central importance to many natural phenomena and technological applications, as will be described in this module. Mole Fraction and Molality Several units commonly used to express the concentrations of solution components were introduced in an earlier chapter of this text, each providing certain benefits for use in different applications. For example, molarity (M) is a convenient unit for use in stoichiometric calculations, since it is defined in terms of the molar amounts of solute species: Because solution volumes vary with temperature, molar concentrations will likewise vary. When expressed as molarity, the concentration of a solution with identical numbers of solute and solvent species will be different 564 11 • Solutions and Colloids Access for free at openstax.org at different temperatures, due to the contraction/expansion of the solution. More appropriate for calculations involving many Colligative Properties are mole-based concentration units whose values are not dependent on temperature. Two such units are mole fraction (introduced in the previous chapter on gases) and molality. The mole fraction, X, of a component is the ratio of its molar amount to the total number of moles of all solution components: By this definition, the sum of mole fractions for all solution components (the solvent and all solutes) is equal to one.
eBook - PDF- Arthur Adamson(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
One of the important applications of colligative phenomena is to the determination of the molecular weight of a solute present in dilute solution. There are a number of other methods for such a determination and these are reviewed in Section 10-7 so as to provide a general picture of this aspect of physical chemistry. Colligative property measurements on nonideal solutions give the thermo-dynamic mole fraction or activity of the solvent and, indirectly, the activity and activity coefficient of the solute. This constitutes a second major application of colligative phenomena and is described in some detail in the Special Topics section. Although appropriate to this chapter, chemical equilibria involving nonelectrolytes are more conveniently discussed in Chapter 12 along with equilibria involving electrolytes. 353 354 CHAPTER 10: DILUTE SOLUTIONS OF NONELECTROLYTES. Colligative Properties TABLE 1 0 -1 . Name of resulting colligative Phases in equilibrium Restriction or condition property Liquid solution vapor Solute must be Vapor pressure nonvolatile lowering Boiling point elevation Solid <=9 liquid solution Solid phase must consist Freezing point of pure solvent depression Liquid solution ^ liquid solvent Semipermeable membrane Osmotic pressure prevents the solute from entering the pure solvent phase 10-1 Vapor Pressure Lowering The general statement for the vapor pressure of the solvent component of a liquid solution is Λ = αΛ° [Eq. (9-71)] or 4^ = 1 - *i > o 0 -1 ) where AP 1 is the vapor pressure lowering of the solvent, P x ° — P 1 . If the solute is nonvolatile, then Ρ is the total vapor pressure above the solution and ΔΡ Χ is the total vapor pressure lowering Δ P. If the solution is ideal, then Raoult's law, Eq. (9-4), holds, which means that a i = x i · Equation (10-1) becomes (10-2) still assuming the solute to be nonvolatile. Thus a measured behavior of the solvent has given the mole fraction of the solute, independent of the chemical nature of the latter.
eBook - PDF- Arther Adamson(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
One of the important applications of colligative phenomena is to the determination of the molecular weight of a solute present in dilute solution. There are a number of other methods for such a determination and these are reviewed in Section 10-7 so as to provide a general picture of this aspect of physical chemistry. Colligative property measurements on nonideal solutions give the thermo-dynamic mole fraction or activity of the solvent and, indirectly, the activity and activity coefficient of the solute. This constitutes a second major application of colligative phenomena and is described in some detail in the Special Topics section. Although appropriate to this chapter, chemical equilibria involving nonelectrolytes are more conveniently discussed in Chapter 12 along with equilibria involving electrolytes. 353 354 CHAPTER 10: DILUTE SOLUTIONS OF NONELECTROLYTES. Colligative Properties TABLE 10-1. Phases in equilibrium Restriction or condition Name of resulting colligative property Liquid solution ^ vapor Solid % liquid solution Liquid solution % liquid solvent Solute must be nonvolatile Solid phase must consist of pure solvent Semipermeable membrane prevents the solute from entering the pure solvent phase Vapor pressure lowering Boiling point elevation Freezing point depression Osmotic pressure 10-1 Vapor Pressure Lowering The general statement for the vapor pressure of the solvent component of a liquid solution is Λ = β Λ ° [Eq. (9-71)] or 4^ = 1 -<*i > O 0 1 ) where AP 1 is the vapor pressure lowering of the solvent, Ρ λ ° — P 1 . If the solute is nonvolatile, then Ρ is the total vapor pressure above the solution and ΔΡ Χ is the total vapor pressure lowering Δ P. If the solution is ideal, then Raoult's law, Eq. (9-4), holds, which means that a x = x 1 . Equation (10-1) becomes (10-2) still assuming the solute to be nonvolatile. Thus a measured behavior of the solvent has given the mole fraction of the solute, independent of the chemical nature of the latter.
eBook - PDF- William R. Robinson, Edward J. Neth, Paul Flowers, Klaus Theopold, Richard Langley(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
Precipitation of the solute is initiated by a mechanical shockwave generated when the flexible metal disk within the solution is “clicked.” (credit: modification of work by “Velela”/Wikimedia Commons) Chapter 11 | Solutions and Colloids 615 This video (http://openstaxcollege.org/l/16handwarmer) shows the crystallization process occurring in a hand warmer. 11.4 Colligative Properties By the end of this section, you will be able to: • Express concentrations of solution components using mole fraction and molality • Describe the effect of solute concentration on various solution properties (vapor pressure, boiling point, freezing point, and osmotic pressure) • Perform calculations using the mathematical equations that describe these various colligative effects • Describe the process of distillation and its practical applications • Explain the process of osmosis and describe how it is applied industrially and in nature The properties of a solution are different from those of either the pure solute(s) or solvent. Many solution properties are dependent upon the chemical identity of the solute. Compared to pure water, a solution of hydrogen chloride is more acidic, a solution of ammonia is more basic, a solution of sodium chloride is more dense, and a solution of sucrose is more viscous. There are a few solution properties, however, that depend only upon the total concentration of solute species, regardless of their identities. These Colligative Properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. This small set of properties is of central importance to many natural phenomena and technological applications, as will be described in this module. Mole Fraction and Molality Several units commonly used to express the concentrations of solution components were introduced in an earlier chapter of this text, each providing certain benefits for use in different applications.
eBook - PDF- Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2015(Publication Date)
- Openstax(Publisher)
Precipitation of the solute is initiated by a mechanical shockwave generated when the flexible metal disk within the solution is “clicked.” (credit: modification of work by “Velela”/Wikimedia Commons) Chapter 11 | Solutions and Colloids 613 This video (http://openstaxcollege.org/l/16handwarmer) shows the crystallization process occurring in a hand warmer. 11.4 Colligative Properties By the end of this section, you will be able to: • Express concentrations of solution components using mole fraction and molality • Describe the effect of solute concentration on various solution properties (vapor pressure, boiling point, freezing point, and osmotic pressure) • Perform calculations using the mathematical equations that describe these various colligative effects • Describe the process of distillation and its practical applications • Explain the process of osmosis and describe how it is applied industrially and in nature The properties of a solution are different from those of either the pure solute(s) or solvent. Many solution properties are dependent upon the chemical identity of the solute. Compared to pure water, a solution of hydrogen chloride is more acidic, a solution of ammonia is more basic, a solution of sodium chloride is more dense, and a solution of sucrose is more viscous. There are a few solution properties, however, that depend only upon the total concentration of solute species, regardless of their identities. These Colligative Properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. This small set of properties is of central importance to many natural phenomena and technological applications, as will be described in this module. Mole Fraction and Molality Several units commonly used to express the concentrations of solution components were introduced in an earlier chapter of this text, each providing certain benefits for use in different applications.
- Martha Mackin(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
13.11b Examples of Colligative Properties A. The vapor pressure of a solution is lower than the vapor pressure of the pure solvent because the presence of solute particles at the surface means that there are fewer solvent molecules at the surface, so fewer can escape. B. The boiling point of a solution is higher than the boiling point of the pure solvent. 1. The vapor pressure of a solution is lower than the vapor pressure of the pure solvent, 2. A higher temperature must be reached before the vapor pressure of the solution is equal to atmospheric? pressure. 3. An increase in the boiling point is related to molality by the follow-ing equation: ^ T b = K b m ^ T b = c ^ a n ^ e boiling temperature m = molality = molal boiling point elevation constant 4. Example: What is the boiling point of a 2.00 m sucrose solution? Unknown Given Connection boiling point of sucrose solution 2.00 m sucrose for water = 0.512 (°C)(kg H 2 0) Δτ, for sucrose b 2.00 m sucrose for water = 0.512 mole solution . η ς ι , ( ° C ) ( J ^ H 2 e) 2.00^e- , n , o„ b = I^&ie- * = l -02 C boiling point of _ j^^j^g p o i n t of water + Δτ for sucrose solution sucrose solution b = 100 °C + 1.024 °C = 101 °C (at 1.00 atm) C. The freezing point of a solution is lower than the freezing point of the pure solvent. 1. A solvent freezes when there is an equilibrium between the liquid and solid forms. 320 Chapter Thirteen 2. At the freezing point the vapor pressure of the liquid solvent must equal the vapor pressure of the pure solid solvent. 3. A solute lowers the vapor pressure of a solution. 4. The lowered vapor pressure means that a lower temperature is required for the solid solvent to be in equilibrium with the liquid solvent of the solution. 5. Depression of the freezing point of a solution is related to molality by the following equation: AT f = K f m AT f = change in freezing temperature m = molality = molal freezing point constant 6.
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
Freezing point depression is a general property of solutions. Further- more, the amount by which the freezing point is depressed is the same for all solutions KEY TERMS Colligative Properties molality (m) LEARNING OBJECTIVE 14.5 • Colligative Properties of Solutions 321 made with a given solvent; that is, each solvent shows a characteristic freezing point depression constant. Freezing point depression constants for several solvents are given in Table 14.5. The solution formed by the addition of a nonvolatile solute to a solvent has a lower freez- ing point, a higher boiling point, and a lower vapor pressure than that of the pure solvent. These effects are related and are known as Colligative Properties. The Colligative Properties are properties that depend only on the number of solute particles in a solution, not on the nature of those particles. Freezing point depression, boiling point elevation, and vapor pressure lowering are Colligative Properties of solutions. The Colligative Properties of a solution can be considered in terms of vapor pressure. The vapor pressure of a pure liquid depends on the tendency of molecules to escape from its sur- face. If 10% of the molecules in a solution are nonvolatile solute molecules, the vapor pressure of the solution is 10% lower than that of the pure solvent. The vapor pressure is lower because the surface of the solution contains 10% nonvolatile molecules and 90% of the volatile solvent molecules. A liquid boils when its vapor pressure equals the pressure of the atmosphere. We can thus see that the solution just described as having a lower vapor pressure will have a higher boiling point than the pure solvent. The solution with a lowered vapor pressure doesn’t boil until it has been heated above the boiling point of the solvent (see Figure 14.8a). Each sol- vent has its own characteristic boiling point elevation constant (Table 14.5).
- Leo J. Malone, Theodore O. Dolter, Steven Gentemann(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
Such a property is known as a colligative property. T b = K b m T f = K f m ' ' The magnitude of the boiling point elevation ( 'T and freezing point lowering ('T ) are given by the equations b f ) 232 where K b and K f are constants characteristic of the solvent and “m” is the molality. Molality is a unit of concentration defined as m = moles of solute kg of solvent Freezing point lowering and boiling point elevation are often used in chemistry laboratories to determine the molar mass of an unknown pure compound. This procedure is illustrated by the following example. Example B-1 Molar Mass by Freezing Point Lowering A pure compound dissolves in water and is found to be a nonelectrolyte. When 50.0 g of this compound is dissolved in 473 g of water, the solution freezes at -2.13 o C. What is the molar mass of the compound? For H 2 O, K f = 1.86 o C . kg/mol. PROCEDURE Calculate the value of T and solve the equation for molality to obtain the molar mass (M.M.): m = mol Solute kg solvent = g solute M.M. g solvent 1000 g/kg Solving for M.M. we get M.M. = 1000 g/kg x g solute g solvent x m SOLUTION Since the freezing point of pure water is 0.00 o C, T f = 0.00 – (-2.13) = 2.13 o C degrees T f = K f m m = T K f = 2.13 o C 1.86 o C . kg mol = 1.15 mol/kg M.M. = 1000 g/kg x 50.0 g 473 g x 1.15 mol/kg = 91.9 g/mol Osmotic pressure, another colligative property, is important in many life processes. The process of osmosis concerns the unequal passage of solvent molecules through a semipermeable membrane separating solutions of different concentrations. We also discussed the effect of electrolytes on Colligative Properties. Since one mole of a solute such as NaCl produces two moles of particles (ions), the effect on Colligative Properties is about twice as much as the effect of one mole of a nonelectrolyte. 233 ASSESSMENT OF OBJECTIVES B-1 Multiple Choice ____ 1.
eBook - PDFChemistry
An Atoms First Approach
- Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste, , Steven Zumdahl, Steven Zumdahl, Susan Zumdahl, Donald J. DeCoste(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
b. When a solute is added to water, the water in solution has a lower vapor pressure than that of pure ice at 08C. c. Colligative Properties depend only on the identity of the solute and not on the number of solute particles present. d. When sugar is added to water, the boiling point of the solution increases above 1008C because sugar has a higher boiling point than water. 26. Is the following statement true or false? Explain your answer. When determining the molar mass of a solute using boiling- point or freezing-point data, camphor would be the best sol- vent choice of all of the solvents listed in Table 10.5. 9. Is molality or molarity dependent on temperature? Explain your answer. Why is molality, and not molarity, used in the equations describing freezing-point depression and boiling- point elevation? 10. Consider a beaker of salt water sitting open in a room. Over time, does the vapor pressure increase, decrease, or stay the same? Explain. A blue question or exercise number indicates that the answer to that question or exercise appears at the back of this book and a solution appears in the Solutions Guide, as found on PowerLecture. Solution Review If you have trouble with these exercises, review Sections 6.1 to 6.3 in Chapter 6. 11. Rubbing alcohol contains 585 g isopropanol (C 3 H 7 OH) per liter (aqueous solution). Calculate the molarity. 12. What mass of sodium oxalate (Na 2 C 2 O 4 ) is needed to prepare 0.250 L of a 0.100-M solution? 13. What volume of 0.25 M HCl solution must be diluted to pre- pare 1.00 L of 0.040 M HCl? 14. What volume of a 0.580-M solution of CaCl 2 contains 1.28 g solute? 15. Calculate the sodium ion concentration when 70.0 mL of 3.0 M sodium carbonate is added to 30.0 mL of 1.0 M sodium bicarbonate. 16. Write equations showing the ions present after the following strong electrolytes are dissolved in water. a. HNO 3 d. SrBr 2 g. NH 4 NO 3 b. Na 2 SO 4 e. KClO 4 h. CuSO 4 c. Al(NO 3 ) 3 f. NH 4 Br i. NaOH Questions 17.
eBook - PDFChemistry
The Molecular Nature of Matter
- Neil D. Jespersen, Alison Hyslop(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
Will the molarity of this solution be numerically larger or smaller than 1.0? Justify your conclusion mathematically. Colligative Properties 12.30 What specific fact about a physical property of a solution must be true to call it a colligative property? 12.31 What is Raoult’s law? 12.32 Why does a nonvolatile solute decrease the vapor pressure of a solvent? Draw a diagram to illustrate your response. 12.33 When octane is mixed with methanol, the vapor pressure of the octane over the solution is higher than what we would calculate using Raoult’s law. Why? Explain the discrepancy in terms of inter- molecular attractions. 12.34 Will a solution of pentane and hexane have an ideal Raoult’s law vapor pressure curve? Explain your answer in terms of intermo- lecular attractions. 12.35 Explain why a nonvolatile solute dissolved in water makes the system have (a) a higher boiling point than water, and (b) a lower freezing point than water. 12.36 Why do we call dialyzing and osmotic membranes semiperme- able? What is the opposite of permeable? 12.37 What is the key difference between dialyzing and osmotic membranes? Draw a diagram to illustrate your response. 12.38 At a molecular level, explain why, in osmosis, there is a net migration of solvent from the side of the membrane less concentrated in solute to the side more concentrated in solute. 12.39 Two glucose solutions of unequal molarity are separated by an osmotic membrane.
eBook - PDF- Stanley E. Manahan(Author)
- 2009(Publication Date)
- CRC Press(Publisher)
waste acid can be calculated. Figure 7.8. Figure 7.8. A buret, a long glass tube with marks on it and a stopcock on the end, is used to meas-A buret, a long glass tube with marks on it and a stopcock on the end, is used to meas-ure the volume of standard solution added to a sample during titration. ure the volume of standard solution added to a sample during titration. Solutions and Solvents 259 Solutions and Solvents 259 7.7. PHYSICAL PROPERTIES OF SOLUTIONS 7.7. PHYSICAL PROPERTIES OF SOLUTIONS The presence of solutes in water can have profound effects upon the properties The presence of solutes in water can have profound effects upon the properties of the solvent. These effects include lowering the freezing point, elevating the boil-of the solvent. These effects include lowering the freezing point, elevating the boil-ing point, and osmosis. All such properties are called ing point, and osmosis. All such properties are called Colligative Properties Colligative Properties ; they ; they depend upon the concentration of solute, rather than its particular identity. The depend upon the concentration of solute, rather than its particular identity. The effects of solutes and solution concentrations on Colligative Properties are addressed effects of solutes and solution concentrations on Colligative Properties are addressed briefly here. briefly here. Freezing Point Depression Freezing Point Depression One of the most practical uses of solutions depends upon the effect that materi-One of the most practical uses of solutions depends upon the effect that materi-als dissolved in water have upon the temperature at which the water, or the solution, als dissolved in water have upon the temperature at which the water, or the solution, freezes. Solutions freeze at lower temperatures than water does. This phenomenon freezes. Solutions freeze at lower temperatures than water does. This phenomenon is applied in the cooling systems of automobiles.
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