chapter_2-20120914.ppt

1、KULeuven Afdeling Fotochemie en Spectroscopie Prof. Dr. F.C. De Schryver,Scanning Electron Micrograph showing a mixture of cells, some with round normal morphology, some with mild sickling showing elongation and bending.,Hemoglobin Solubility and Sickle-Cell Anemia,KULeuven Afdeling Fotochemie en Sp

2、ectroscopie Prof. Dr. F.C. De Schryver,Hemoglobin is the substance in red blood cells that carries oxygen. Hemoglobin is normally present in solution within the red blood cells. But in people with sickle-cell anemia, the unoxygenated hemoglobin readily comes out of solution. It produces a fibrous pr

3、ecipitate that deforms the cell, giving it the characteristic sickle shape. Hemoglobins are large molecules (molecular weight about 64,000 amu) consisting of four protein chains, two of one kind ( chains) and two of another kind ( chains). Normal and sickle-cell hemoglobins are almost exactly alike,

4、 except that each chain of the hemoglobin responsible for sickle-cell anemia differs from normal hemoglobin in one place.,KULeuven Afdeling Fotochemie en Spectroscopie Prof. Dr. F.C. De Schryver,In this place, the normal hemoglobin has the group which helps confer water solubility on the molecule be

5、cause of the polarity of the group and its ability to form hydrogen bonds. The abnormal hemoglobin has the following hydrocarbon group:,Hydrocarbon groups are nonpolar. This small change makes the molecule less water-soluble.,KULeuven Afdeling Fotochemie en Spectroscopie Prof. Dr. F.C. De Schryver,L

6、inus Pauling(1901-1994) 莱纳斯鲍林,In 1949 Linus Pauling showed that people with sicklecell anemia have abnormal hemoglobin.,Nobel Prize in Chemistry (1954)Nobel Peace Prize (1962),KULeuven Afdeling Fotochemie en Spectroscopie Prof. Dr. F.C. De Schryver,Linus Paulings book, How to Live Longer and Feel Be

7、tter, advocated very high intake of Vitamin C.,Chapter 2. Colligative properties of Dilute Solutions, 2-1. Vapor-pressure lowering 2-2. Boiling-point elevation and Freezing-point depression 2-3. Osmosis,Physical properties of a solution that depend on the nature of the solute: Color, conductivity, e

8、tc.,Introduction,Physical properties of solutions that depend only on the concentration of solute molecules or ions in solution but not on the chemical identity of the solute are called colligative properties (依数性).,Vapor-pressure lowering (蒸气压下降); Boiling-point elevation (沸点升高); Freezing-point depr

9、ession (凝固点降低); Osmotic pressure (渗透压).,1. Vapor-Pressure Lowering,I. Gas pressure and its measurement,1. Vapor-Pressure Lowering,The pressure (压强), P, of a gas is the force, F, exerted by the gas divided by the area, A, on which the force is exerted.,The SI unit of pressure, kg/(ms2), is given the

10、name pascal (Pa).,The pressure exerted by the atmosphere is about 100,000 Pa. Thus, the pascal is an extremely small unit.,1. Vapor Pressure Lowering,A barometer (气压计) is a device for measuring the pressure of the atmosphere.,The mercury barometer consists of a glass tube about one meter long, fille

11、d with mercury and inverted in a dish of the same liquid metal.,At sea level the mercury in the tube falls to a height of about 760 mm above the level in the dish. This height is a direct measure of the atmospheric pressure.,Why mercury ?,KULeuven Afdeling Fotochemie en Spectroscopie Prof. Dr. F.C.

12、De Schryver,Evangelista Torricelli (1608-1647) 埃万杰利斯塔托里拆利,the first scientific description of the cause of wind: . winds are produced by differences of air temperature, and hence density, between two regions of the earth,KULeuven Afdeling Fotochemie en Spectroscopie Prof. Dr. F.C. De Schryver,风 李峤（唐

13、） 解落三秋叶， 能开二月花。 过江千尺浪， 入竹万竿斜。,1. Vapor-Pressure Lowering,A manometer (压力计) is a device that measures the pressure of a gas or liquid in a vessel.,Why mercury ?,A flask equipped with a closed-tube manometer. The gas pressure in the flask is proportional to the difference in heights between the liquid

14、 levels in the manometer, h.,1. Vapor-Pressure Lowering,The general relationship between the pressure P and the height h of a liquid column in a barometer or manometer is:,g: the constant acceleration of gravity (9.81 ms-2); d: the density of the liquid in the manometer.,Why mercury ?,1. Vapor-Press

15、ure Lowering,The unit millimeters of mercury (mmHg) is a unit of pressure equal to that exerted by a column of mercury 1 mm high at 0.00 C.,The atmosphere (atm) is a related unit of pressure equal to exactly 760 mmHg.,Scientists also use a unit call the bar (巴): 1 bar = 105 pa. The name bar is deriv

16、ed from the Greek word for “heavy.”,Blood pressure,SI units of blood pressure is suggested.,1 kPa 7.50 mmHg,1. Vapor-Pressure Lowering,I. Vapor pressure (蒸气压),1. Vapor-Pressure Lowering,Vaporization (蒸发) is the change of a liquid to the vapor.,Condensation (凝结) is the change of a gas to the liquid.,

17、The Vapor pressure of a liquid is the pressure of the vapor over the liquid, measured at equilibrium at a given temperature in a closed vessel.,Vaporization and condensation,1. Vapor-Pressure Lowering,There is a trace of mercury vapor present, but so little that we can ignore it.,1. Vapor-Pressure L

18、owering,Vapor pressure is a function of nature of solvent and temperature.,Vapor pressure of water under different temperature,P T curves for different solvent,II. Volatility (挥发性) of substances,1. Vapor-Pressure Lowering,Solid also has its vapor pressure due to sublimation (升华) (ice, iodine, and na

19、phthalene). Generally, solid has low vapor pressure.,Volatile substances: a substance with relatively high vapor pressure at normal temperatures. Nonvolatile substances: a substance with relatively low vapor pressure at normal temperatures.,Naphthalene (萘) is used to make mothballs.,Water at 20 C ha

20、s a vapor pressure of 17.54 mmHg. An aqueous solution containing 0.010 mole fraction of ethylene glycol (乙二醇, CH2OHCH2OH) has a vapor pressure of 17.36 mmHg.,III. Vapor-pressure lowering (蒸气压降低),1. Vapor-Pressure Lowering,Vapor-pressure lowering of a solvent equals the vapor pressure of the pure sol

21、vent minus the vapor pressure of the solution.,The vapor-pressure lowering, P, of water is:,1. Vapor-Pressure Lowering,Vapor leaves the solution on the left (which becomes more concentrated) and condenses on the solution on the right (which becomes less concentrated), and after some time, the two so

22、lutions become equal in concentration and in vapor pressure.,Raoults law: The vapor pressure of a solution, P, equals the vapor pressure of the pure solvent, P0, times the mole fraction of solvent, xA, in the solution.,IV. Raoult law,1. Vapor-Pressure Lowering,P = P0 xA,Notes:,1. Vapor-Pressure Lowe

23、ring,The solution is dilute. The solute is nonvolatile. The solute is nonelectrolyte (非电解质).,P = P0 xA,Because the mole fraction of solvent in a solution is always less than 1, the vapor pressure of the solution of a nonvolatile solute is less than that for the pure solvent, the vapor pressure is lo

24、wered.,KULeuven Afdeling Fotochemie en Spectroscopie Prof. Dr. F.C. De Schryver,Plot of vapor pressures of solutions showing Raoults law Vapor pressures of solvent A for two solutions have been plotted against mole fraction of solvent. In one case (labeled “ideal solution”), the vapor pressure is pr

25、oportional to the mole fraction of solvent for all mole fractions; it follows Raoults law for all concentrations of solute. For the “nonideal solution,” Raoults law is followed for low solute concentrations (mole fraction of solvent near 1), but the vapor pressure deviates at other concentrations.,F

26、or dilute solution: nAnB then nA+nBnA,P = P0 P = P0 P0 xA= P0(1 xA) = P0 xB K bB,V. Vapor-pressure lowering of dilute solution,1. Vapor-Pressure Lowering,Vapor-pressure lowering: a colligative property.,Example 2-1: Calculate the vapor-pressure lowering of water when 5.67g of glucose, C6H12O6, is di

27、ssolved in 25.2g of water at 25C. The vapor pressure of water at 25C is 23.8 mmHg. What is the vapor pressure of the solution?,1. Vapor-Pressure Lowering,The mole fraction of glucose is:,Therefore, the vapor-pressure lowering is:,The vapor pressure of the solution is:,Solution:,KULeuven Afdeling Fot

28、ochemie en Spectroscopie Prof. Dr. F.C. De Schryver,Exercise: 2-1 Naphthalene, C10H8, is used to make mothballs. Suppose a solution is made by dissolving 0.515 g of naphthalene in 60.8 g of chloroform, CHCl3. Calculate the vapor-pressure lowering of chloroform at 20 from the naphthalene. The vapor p

29、ressure of chloroform at 20 is 156 mmHg. Naphthalene can be assumed to be nonvolatile compared with chloroform. What is the vapor pressure of the solution?,29,naphthalene 萘,p-dichorobenzene 对-二氯苯,camphor 樟脑,Density: 0.99 mp: 177,Density: 1.2417 mp: 53.1,Density: 1.162* mp: 80.6 ,* pure naphthalene,

30、density: 0.997,KULeuven Afdeling Fotochemie en Spectroscopie Prof. Dr. F.C. De Schryver,KULeuven Afdeling Fotochemie en Spectroscopie Prof. Dr. F.C. De Schryver,I. Boiling point of a liquid,2. Boiling-P. Elevation and Freezing-P. Depression,Boiling point (沸点) of a liquid is the temperature at which

31、the vapor pressure of this liquid equals the pressure exerted on the liquid (atmospheric pressure, unless the vessel containing the liquid is closed.),Boiling point relates to the nature of liquid. Boiling point relates to atmospheric pressure. Normal boiling point: Atmospheric pressure equals to 10

32、1.3 kPa.,2. Boiling-P. Elevation and Freezing-P. Depression,Boiling points of diethyl ether, ethanol, and water.,Red: higher atmospheric pressure; Blue: lower atmospheric pressure.,The boiling point of water at sea level (1.0 atm) is 100 C. But at 1600 m above sea level (0.83 atm), the boiling point

33、 of water is 95 C.,2. Boiling-P. Elevation and Freezing-P. Depression,II. Boiling-point elevation (沸点升高),2. Boiling-P. Elevation and Freezing-P. Depression,The addition of nonvolatile solute to a liquid reduces its vapor pressure, the temperature must be increased to a value greater than the normal

34、boiling point to achieve a vapor pressure of 101.3 kPa.,Kb: Boiling-point-elevation constant. It depends only on the solvent.,2. Boiling-P. Elevation and Freezing-P. Depression,The boiling-point elevation, Tb, is a colligative property of a solution equal to the boiling point of the solution minus t

35、he boiling point of the pure solvent.,KULeuven Afdeling Fotochemie en Spectroscopie Prof. Dr. F.C. De Schryver,A person with a fever has a temperature of 102.5 F, what is this temperature in degrees Celsius?,2. Boiling-P. Elevation and Freezing-P. Depression,Ethanol has a boiling-point-elevation con

36、stant (Kb) of 1.22 Kkgmol-1. This means that a 0.100 molkg-1 solution of a nonvolatile, undissociated solute in ethanol boils at 0.122 K(C) above the boiling point of pure ethanol. Pure ethanol boils at 78.4 C, so a 0.100 molkg-1 solution boils at 78.4 C + 0.122 C = 78.5 C .,III. Freezing point,2. B

37、oiling-P. Elevation and Freezing-P. Depression,The temperature at which a pure liquid changes to a crystalline solid, or freeze, is called the freezing point (凝固点). At this temperature, the vapor pressure of the liquid equals to that of the solid state.,The temperature at which a crystalline solid c

38、hanges to a liquid, or melts, is called the melting point (熔点). The freezing point of a liquid is identical to the melting point of the solid.,2. Boiling-P. Elevation and Freezing-P. Depression,Determination of the freezing point of a liquid. The liquid is cooled by means of a freezing mixture. To c

39、ontrol the rate of temperature decrease, the liquid is separated from the freezing mixture by an air space.,2. Boiling-P. Elevation and Freezing-P. Depression,Usually it is the pure solvent that freezes out of solution. For that reason, the vapor-pressure curve for the solid is unchanged. Therefore,

40、 the freezing point shifts to a lower temperature.,IV. Freezing-point depression (凝固点降低),2. Boiling-P. Elevation and Freezing-P. Depression,Kf: Freezing-point-depression constant. It depends only on the solvent.,The freezing-point depression, Tf, is a colligative property of a solution equal to the

41、freezing point of the pure solvent minus the freezing point of the solution.,Example 2-2: An aqueous solution is 0.020 molL-1 glucose. What is the freezing-point-depression of this solution?,2. Boiling-P. Elevation and Freezing-P. Depression,Solution:,Kf for water is 1.86 Kkgmol-1, therefore,A conce

42、ntration of 0.020 molL-1 corresponds to a concentration of 0.020 molkg-1.,This solution freezes at 0.037 C.,Example 2-3: 0.638 g of urea is dissolved in 250 g of water, the determined freezing-point-depression of the solution is 0.079 K. Calculate the molar mass of urea.,2. Boiling-P. Elevation and

43、Freezing-P. Depression,Solution:,V. Practical applications of freezing-point depression,1. Determine the molar mass of a solute. The molar mass of a solute can also be determined by boiling-point-elevation method and freezing-point-depression method, why freezing-point-depression method is preferred

44、 ? 2. Spreading soluble salt such as NaCl,CaCl2, on an snowy (or icy) road lowers the freezing point of water, causing snow (or ice) to melt. .,2. Boiling-P. Elevation and Freezing-P. Depression,3. Automobile antifreeze mixtures,2. Boiling-P. Elevation and Freezing-P. Depression,The main ingredient

45、of automobile antifreeze mixtures is ethylene glycol (EG), CH2OHCH2OH is used in automobile radiators as an antifreeze because it lowers the freezing point of the coolant (散热剂). EG has low vapor pressure, so it does not easily vaporize away. It is relatively cheap, being manufactured from ethylene,

46、C2H4, which is obtained from petroleum. It has a sweet taste but is poisonous.,For 0.0100 molkg-1 NaCl aqueous solution:,2. Boiling-P. Elevation and Freezing-P. Depression,VI. Colligative properties of ionic solutions,Calculated Tf:0.0186 K Measured Tf:0.0360 K,It is the total concentration of ions

47、(离子), rather than the concentration of ionic substance, that makes sense to the colligative properties of solutions.,i is called the vant Hoff factor. It is about the number of ions resulting from each formula unit. NaCl, MgCl2.,2. Boiling-P. Elevation and Freezing-P. Depression,Example 2-4: Estimat

48、e the freezing point of a 0.010 molkg-1 aqueous solution of aluminum sulfate, Al2(SO4)3.,Solution:,The vant Hoff factor i = 5,The estimated freezing point of the solution is:,2. Boiling-P. Elevation and Freezing-P. Depression,Concept Check,Each of the following substance is dissolved in a separate 1

49、0.0-L container of water: 1.5 mol NaCl, 1.3 mol Na2SO4, 2.0 mol MgCl2, and 2.0 mol KBr. Without doing extensive calculations, rank the boiling point of each of the solutions from highest to lowest.,3. Osmosis,What is the concentration of the physiological saline solution ?,9.0 gL-1 NaCl,Why ?,3. Osm

50、osis,Diffusion (扩散): Movement of a fluid from an area of higher concentration to an area of lower concentration.,Diffusion is a result of the kinetic properties of particles of matter. The particles will mix until they are evenly distributed.,I. Osmotic phenomenon and osmotic pressure,3. Osmosis,3.

51、Osmosis,Osmosis (渗透): is the phenomenon of solvent flow through a semi-permeable membrane to equalize the solute concentrations on both sides of the membrane.,The name osmosis comes from the Greek word for “push.”,Two requirements for osmosis:,3. Osmosis, Concentration difference: diffusion Semiperm

52、eable membrane: one-directional diffusion.,Osmotic pressure (渗透压，) of a solution equals to the pressure that, when applied to the solution, just stops osmosis.,The glucose solution continues to rise up the funnel stem until the downward pressure exerted by the solution above the membrane eventually

53、stops the upward flow of solvent (water).,KULeuven Afdeling Fotochemie en Spectroscopie Prof. Dr. F.C. De Schryver,Jacobus Henricus van t Hoff (1852-1911) 雅各布斯亨里克斯范托夫,The Nobel Prize in Chemistry 1901,Chemical kinetics, Stereochemistry,II. Vant Hoff formula:,3. Osmosis,At a fixed temperature, Osmoti

54、c pressure of a solution is proportional to its concentration, independent of the identities of the solute.,: osmotic pressure of the solution cB: amount-of-substance concentration R: gas constant, 8.314 J mol-1 K-1 T: absolute temperature,Osmotic pressure is one of colligative properties of a solut

55、ion.,Example 2-5: Calculate the osmotic pressure of a 50.0 mL solution containing 2.00 g of sucrose (C12H22O11) at 37.,3. Osmosis,The MB of sucrose is 342 g mol-1, then:,Solution:,Osmotic pressure and freezing-point depression,0.020 mol L-1 glucose solution,Freezing-point depression: 0.037 C,Osmotic

56、 pressure:,If this pressure were to be exerted by a column of a water solution, the column would have to be more than 4.5 m high.,3. Osmosis,3. Osmosis,Example 2-6: Calculate the osmotic pressure of 9.00 g L-1 physiological saline solution at 310K.,Solution:,Osmotic pressure of ionic solutions:,NaCl

57、 Na+ + Cl-,Example 2-7: The osmotic pressure of a solution containing 1.00 g hemoglobin in 100 mL pure water is 0.366 kPa at 20. What is the molar mass of the compound?,3. Osmosis,Solution:,3. Osmosis,Example 2-8: The measured freezing point of tear is -0.52 . Determine the osmotic pressure of tear

58、at 37.,Solution:,Osmotic active substance (渗透活性物质): Solute particles (molecules, ions) that generate osmosis effect.,3. Osmosis,III. Significance of osmotic pressure in medical sciences,1. Osmolarity (渗透浓度),Osmolarity (cos): The total amount-of-substance (molar) concentration of osmotic active subst

59、ances. Unit: mol L-1 or mmol L-1,3. Osmosis,Example 2-9: Calculate the osmolarity of 9.00 gL-1 NaCl solution and 50.0 gL-1 glucose solution.,Solution:,NaCl Na+ + Cl-,3. Osmosis,Osmolarities of osmotic active substance in normal blood plasma,2. Isotonic, hypertonic, and hypotonic solution,3. Osmosis,The osmolarity of the solution is equal to that of the cell; the cell has its normal round shape with depressed center.,Isotonic solution (等渗溶液),Cell membrane: a semipermeable membrane,3. Osmosis,Hypotonic solution (低渗溶液),The osmolarity of the solution is less than tha